GB2159519A

GB2159519A - 7-Oxo-4-thia-1-azabicyclo[3,2,0]heptane derivatives; azetidinones

Info

Publication number: GB2159519A
Application number: GB08516150A
Authority: GB
Inventors: Barry Clive Ross; Graham Johnson
Original assignee: Hoechst UK Ltd
Current assignee: Sanofi Aventis UK Holdings Ltd
Priority date: 1982-03-26
Filing date: 1985-06-26
Publication date: 1985-12-04
Also published as: GB2159519B; GB8516150D0

Abstract

Intermediates in the preparation of 7-oxo-4-thia-1-azabicyclo[3,2,0] heptane derivatives have the formulae:- <IMAGE> or are lactones of the above compounds where R<2>a = R<2>b = OH or are cyclic thioesters of the above compounds (ie R<2>a + R<2>b = A), in which R<1>, R<2>a, R<2>b, A, R<3> and R<4> are various defined groups.

Description

SPECIFICATION 7-Oxo"4-thia-1-azabicyclo[3,2,0]heptane derivatives The present invention relates to certain intermediates for the preparation of 7-oxo-4-thia-1azabicyclo[3,2,0]heptane and hept-2-ene derivatives, and to a process for their preparation.

7-Oxo-4-thia-1-azabicyclo[3,2,0]heptane and 7-oxo-4-thia-1-azabicyclo[3,2,0]hept-2-ene penem have the following structures:

Certain derivatives of these basic structures have antibiotic properties, see, for example, British Patent Applications Nos. 2 074 563, 2042 520 and 2 013674. There are, however, disadvantages in the methods proposed for synthesising such compounds, for example, the low yields generally achieved, which are exacerbated by the isomeric composition of the product: it is well known that certain stereochemistry in penem compounds is desirable as isomers having this stereochemistry are more biologically active than other isomers.Many of the processes proposed for the production of penem derivatives and their precursors do not give predominantly the desired isomers, and the search continues for more effective methods of synthesising these structures.

The present invention relates to a compound of the general formula la and itstautomer Ib

in which formulae R represents a carboxyl esterifying group, for example, a carboxyl esterifying group that may be removed by hydrolysis, photolysis, reduction or enzyme action to give the free acid.

The term "a compound of the general formula I" and "a compound of formula I" are both used herein to denote a compound of the general formula la, a compound of the general formula Ib, or any mixture thereof.

"A compound of formula II" is used to denote collectively compounds of formulae Ila, llb and llc. The terms "a compound of formula III" and "a compound of formula IV" are used analogously.

The present invention also provides a process for the production of a compound of the general formula I, which comprises treating a compound of the general formula lia, llb, or llc.

in which R is as defined above, R1 represents a chlorine or bromine atom, the radicals R2a and R2, which may be the same or different, each represents an alkyl group having from 1 to 4 carbon atoms, especially a methyl or t-butyl group, an aryl group, especially a phenyl group, or an aralkyl group, especially a benzyl group, and A represents a direct bond or the residue of a dicarboxylic acid, with a base.

The base used in the above reaction must be capable of splitting a sulphur-carbonyl bond in the compound of formula II and of bringing about ring closure. The base may be inorganic or organic, for example, ammonia, or an alkali metal (especially a sodium or potassium) carbonate, bicarbonate, or hydroxide; a primary amine, for example, methylamine, ethylamine, aniline or benzylamine; an alkali metal alkoxide, for example, sodium methoxide; or a heterocyclic base, for example, having a pKa within the range of from 5 to 9, for example, imidazole or pyridine or a substituted pyridine, for example, an alkyl-, amino-, or alkylamino-substituted pyridine, for example, 4-methyl- or 4-dimethylamino-pyridine. Imidazole is particularly preferred.

The reaction is generally carried out in a solvent or diluent, the choice of which is wide, provided that it is inert under the reaction conditions. Examples of solvents and diluents are oxygenated hydrocarbons, for example, alcohols, for example, having up to 4 carbon atoms, for example, methanol and ethanol; ethers, for example, having up to 4 carbon atoms, for example, diethyl ether, also tetrahydrofuran and dioxane; ketones, for example, having up to 4 carbon atoms, for example acetone and methyl ethyl ketone; esters, for example, methyl acetate and ethyl acetate; and amides, for example, dimethylformamide and dimethylacetamide; also chlorinated hydrocarbons, for example, chloroform, methylene chloride and carbon tetrachloride; aromatic hydrocarbons, for example, benzene and toluene; and other solvents, for example, acetonitrile and nitromethane.A mixture of any two or more solvents may be used, and solvents are preferably used in admixture with water, preferably a water-miscible solvent in admixture with 5 to 20 % (viv) water, especially a mixture of dioxane and water, preferably 5 to 10 % (v/v) water.

The reaction is generally carried out at a temperature within the range of from 0 to 40 C, preferably from 0 to 20"C.

An esterified carboxyl group -COOR is, for example, an ester formed with an unsubstituted or substituted aliphatic, cycloaliphatic, cycloaliphatic-aliphatic, aryl, araliphatic, heterocyclic or heterocyclic-aliphatic alcohol having up to 20 carbon atoms, or is, for example, s silyl or stannyl ester.

R may represent, for example a straight or branched chain substituted or unsubstituted alkyl, alkenyl or alkynyl group having up to 18 carbon atoms, preferably up to 8 carbon atoms, and especially up to 4 carbon atoms, for example, a methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl, tert-butyl, n-pentyl, n-hexyl, allyl, or vinyl group.

An aliphatic group R, especially a methyl group, may be substituted by a cycloalkyl, aryl or heterocyclic group, or R may itself represent a cycloalkyl, aryl or heterocyclic group.

A cycloaliphatic group R may have up to 18 carbon atoms and is, for example, a cyclopentyl, cyclohexyl or adamantyl group. An aryl group may have up to 12 carbon atoms and may have two or more fused rings. An aryl group R is, for example, an unsubstituted or substituted phenyl group, and an unsubstituted or substituted aralkyl group is, for example, a benzyl,p-nitrobenzyl or benzhydryl group.

A heterocyclic group may have one or more heteroatoms, selected from oxygen, nitrogen and sulphur, and up to 14 atoms in total. A heterocyclic group is, for example, an oxygen-containing heterocyclic group, for example, a tetrahydropyranyl or phthalidyl group.

A stannyl group R may have up to 24 carbon atoms, for example, R may represent a stannyl group having three substituents ,which may be the same or different, selected from alkyl, alkenyl, cycloalkyl, aryl, aralkyl, alkoxy and aralkoxy groups, for example, alkyl groups having up to 4 carbon atoms, for example, n-butyl groups, phenyl and benzyl groups, especially three n-butyl groups.

A silyl group R may also have up to 24 carbon atoms and three substituents, which may be the same or different, selected from alkyl, alkenyl, cycloalkyl, aryl and aralkyl groups, for example alkyl groups having up to 4 carbon atoms, for example, methyl and t-butyl groups.

Any group R that is capable of substitution may be substituted, for example, with a halogen atom, especially a chlorine or bromine atom, or a nitro group.

The group R may be removable by hydrolysis, by photolysis, by reduction or by enzyme action to give the free acid, or two or more methods may be used, for example, reduction followed by hydrolysis. A group R that may be removed readily without substantial degradation of the rest of the molecule is particularly useful as a carboxyl protecting group. Examples of esters that are readily split by reduction are arylmethyl esters, for example, benzyl,p-nitrobenzyl, benzhydryl and trityl esters.

A stannyl ester, for example, a tri-n-butyl stannyl ester, may be split readily by hydrolysis, for example, by solvolysis, for example, using water, an alcohol, a phenol or a carboxylic acid, for example, acetic acid.

Certain ester groups may be split off by base hydrolysis, for example, acetylmethyl and acetoxymethyl ester groups.

There may be used an esterifying group that is removable under physiological conditions, that is to say, the esterifying group is split off in vivo to give the free acid or the carboxylate, for example, an acyloxymethyl ester, e.g. an acetoxymethyl or pivaloyloxymethyl ester, an aminoalkanyloxymethyl ester, for example, an L-glycyloxymethyl, L-valyloxymethyl or L-leucyloxymethyl ester, or a phthalidyl ester, or an optionally substituted 2-aminoethyl ester, for example, a 2-diethylamino-ethyl or 2-(1 -morpholino)-ethyl ester.

Preferred esters are the p-nitrobenzyl, phthalidyl, pivaloyloxymethyl, acetylmethyl and acetoxy-methyl esters.

A compound of the general formula Ila, llb, or llc is preferably produced by halogenating a compound of the general formula Illa, Illb or Illc, respectively.

in which R, R2a R2b and A are defined as above, and R3 represents an alkyl group having from 1 to 8, preferably from 1 to 6, and especially from 1 to 4 carbon atoms, for example, an ethyl group, or an alkenyl group having up to 6 carbon atoms, especially an allyl group.

The halogenation of a compound of formula Illa, Illb or Illc is carried out with an agent capable of splitting a carbon-sulphur bond and introducing a halogen atom. Such agents are well known in the art and include, for example, molecular chlorine, molecular bromine, sulphuryl chloride, sulphuryl bromide, t-butyl hypochlorite and cyanogen chloride.

The halogenating agent is generally used in an amount of from 1 to 2 mole equivalents, calculated on the compound of formula Ill. The reaction is generally carried out at a temperature within the range of from -40 to +20 C. The reaction is generally carried out in a solvent or diluent that is aprotic and is inert under the reaction conditions, for example, an ether, a hydrocarbon or a halogenated hydrocarbon, for example, dioxane, benzene, chloroform or methylene chloride. A mixture of two or more solvents may be used.

Examples of halogenating systems are: chlorine in chloroform and, especially, chlorine in benzene and t-butyl hypochlorite in benzene. In the latter two cases, the temperature is preferably from 5 to 200C, and especially from Sto 10"C.

A compound of formula Illa, Illb, or Illc is preferably produced by removing the protective group from a compound of formula IVa, IVb or IVc, respectively,

in which R, R2a Rb, R3 and A are defined as above, and R4 denotes a hydroxy protecting group.

Preferred groups R4 are those which are compatible with the synthesis of the compond of formula IV and which may be removed under reaction conditions in which the resulting compound Ill is stable. Compound Ill has been found to be stable in the presence of a proton source, for example, hydrogen chloride, aqueous hydrochloric acid or aqueous hydrofluoric acid. Accordingly, one type of preferred hydroxy protecting groups R4 are those which may be removed under acidic conditions.Such groups are well known in the art and are for example, tetrahydropyranyl and tetrahydrofuranyl groups; acetal and ketal groups, for example of formula

in which R3 and Rq which may be the same or different, each represents a hydrogen atom or a lower alkyl group, preferably a methyl group, or Re and R7 together with the carbon atom to which they are attached represent a ring having from 4 to 7 carbon atoms, for example, a tetrahydropyranyl or tetra hydrofuranyl ring; and R5 represents a lower alkyl group, preferably a methyl or ethyl group.

R4 may also represent a silyl group, for example, as described above in relation to R, for example, -SiR3R9R10 groups, in which R8, Rs and R , which may be the same or different, each represents a lower alkyl group or an aryl group, for example, triethylsilyl, t-butyldimethylsilyl and methyldiphenylsilyl groups; and stannyl groups, for example, as described above in relation to R, for example, SnR11R12R13 groups, in which R11, R12 and R13, which may be the same or different, each represents a lower alkyl group, for example, a tri-n-butylstannyl group. Preferred R4 groups are tetrahydropyranyl, 2-methoxyprop-2yl and tbutyldimethylsilyl groups.

A t-butyidimethylsilyl group may be removed in a known manner by acid hydrolysis, for example, using moderately concentrated hydrochloric acid, for example 6M HCI, e.g., in tetrahydrofuran (cf Belgian Patent Specification No. 881 012), or hydrogen chloride in tetrahydrofuran, dimethylformamide, dioxane, a lower alkanol, or acetonitrile; tetra(n-butyl)ammonium fluoride in an acidic medium, e.g., in acetic acid (cf Belgian Patent Specification No. 882764); or aqueous hydrogen fluoride e.g., in the presence of acetonitrile (cf J.

Chem. Soc. Perkin 1, 1981, 2055). (The term 'known' is used herein to mean in actual use in the art or described in the literature of the art).

A compound of the general formula IV may be prepared according to the following reaction scheme:

in which R, Era2, R2b, R3, R4 and A are as defined above.

A compound of formula VII may be prepared as described in Belgian Patent Specification No. 882764.

A compound of formula VII may be converted into a compound of formula Vl by reaction with a compound of formula VIII R3 - S - R14 (VIII) in which R3 is as defined above and R14 represents a hydrogen atom or an alkali metal atom, especially a sodium or potassium atom. R3 preferably represents a straight chain lower alkyl group, especially an ethyl group, or a straight chain lower alkenyl group, especially an allyl group.

The reaction is generally carried out in a solvent, preferably a protic solvent, for example, water or an alcohol, or an aprotic, water-miscible solvent which is preferably polar, for example, dimethylformamide, dimethyl sulphoxide, tetrahydrofuran or dioxan. The reaction temperature is, for example, from -20 to +50, preferably from -10 to +20"C.

To obtain a compound of formula V a compound of formula VI may be reacted, in the presence of a base, with a compound of formula IX Y1CH2CO2R (IX) in which R is as defined above and Y' represents a group that is capable of being replaced by a nucleophilic group and is, for example, a halogen atom, preferably a bromine or iodine atom, or a modified hydroxy group, preferably a sulphonyloxy group of the formula SO3R16 in which R16 represents a lower alkyl or -CF3 group, or a phenyl group which is unsubstituted or is substituted by a p-nitro, p-bromo orp-methyl group.

Y1 preferably represents a bromine or iodine atom or a methylsulphonate, trifluoromethylsulphonate, tolylsulphonate or benzenesulphonate group.

The base may be inorganic, organic or organometallic, for example, an alkali metal or alkaline earth metal hydroxide, oxide, carbonate, bicarbonate or hydride, for example, sodium hydroxide, magnesium oxide, potassium carbonate, potassium bicarbonate or sodium hydride; a tertiary amine, for example, a Lriialkylamine, for example, triethylamine, DABCO (diazabicyclo[2,2,2]octane), pyridine, or an alkylsubstituted or amino-substituted or dialkylamino-substituted pyridine, for example, N,Ndimethylaminopyridine, or collidine; a guanidine, for example, tetramethylguanidine;DBN (diazabicyclo [4,3,0]non-5-ene) or DBU (diazabicyclo(5,4,0]undec-7-ene), a polymeric base i.e., a base attached to an inert polymeric support e.g., Hunig's base (diisopropylethylamine attached to e.g., polystyrene); a metallated amine, for example, a metallated alkyl- or arylamine, for example, lithium diisopropylamide (LDA), lithium hexamethyldisilazide, lithium piperidide, lithium 2,2,6,6-tetramethylpiperidide, or a Grignard reagent, for example, methylmagnesium bromide. Preferred bases are, for example, potassium carbonate, sodium hydride, lithium diisopropylamide and triethylamine.

The reaction is generally carried out in an aprotic solvent or diluent, for example, a tertiary amide, for example, dimethylformamide, dimethylacetamide or hexamethylphosphoramide; a hydrocarbon, for example, benzene ortoluene; or an ether, for example, diethyl ether, tetrahydrofuran or dioxane; or acetonitrile, dimethyl sulphoxide, or sulpholane. Dimethylformamide and dimethylacetamide are preferred.

A mixture of two or more solvents and/or diluents may be used.

The reaction may be carried out at a temperature generally within the range of from -80 C to +30"C preferably from -40 to +30"C, and especially from -20 to +200C.

From 1 to 1.5 moles of compound IX are preferably used per mole of compound VI especially from 1 to 1.1 moles of IX per mole of VI. The base is used in an amount, for example, from 1 to 4 moles of base per mole of compound VI.

The reaction is preferably carried out by dissolving compound VI in a solvent, advantageously in dimethylformamide with stirring, adding the base, adding the compound of formula IX and reacting at the desired temperature. The resulting compound of formula V may be worked up and isolated in the usual manner, for example, using chromatographic and/or crystallisation techniques, or the subsequent reaction may be carried out directly on the resulting reaction mixture after removal of any solvent that is not compatible with the subsequent reaction.

If R in formula V represents a carboxyl esterifying group, this group may be converted into another esterifying group R, for example, to introduce a group R that is more easily removable under desired conditions. This transesterification is generally carried out as follows: the ester for formula V is hydrolysed in a known manner using, for example, acid or alkaline hydrolysis, preferably using an alkali metal hydroxide, especially sodium or potassium hydroxide. The ester of formula V, for example, a methyl ester, is preferably hydrolysed using an alkali metal hydroxide, especially one mole thereof per mole of the ester of formula V in a solvent, for example ethanol, methanol or water, or an aqueous-organic solvent, for example, tetrahydrofu ra n/water, ethanol/water, or acetonitri le/water.

The reaction mixture may then be acidified to give a solution of pH 1 to 5, preferably 2 to 4, and the free acid may then be isolated and, if desired, the free acid is then esterified with an esterifying agent capable of introducing a different esterifying group R, for example with an alcohol ROH in the presence of an acid or another activating agent, for example, dicyclohexylcarbodiimide, or with an alkylating agent RY1 in which Y' is as defined above. Preferably a salt may be isolated and esterified directly.

A compound of formula V may be converted into a compound of formula IV by treatment with a base in the presence of carbon disulphide followed by reaction with an acylating agent, or by treatment with a base, then with carbon disulphide, and finally reaction with an acylating agent. An acylating agent is generally an activated carboxylic acid.

The activated carboxylic acid may be any activated acid derivative comprising the group R2. Such derivatives are well known in the art, and include acid halides, acid anhydrides, and activated esters. An anhydride may be symmetrical or asymmetrical.

Forthe introduction of a group

to give a compound of formula IVa, the acylating agent preferably has one of the formulae Xa to Xb Ra2COZ (Xa) Rb2COZ (Xb)

in which R2a and R2b are as defined above, and Z represents a halogen atom, especially a chlorine or bromine atom or represents an activated ester or amide, or a radical derived from an acid azide. Such coupiing reagents are well known in the art of peptide chemistry.

In the case of formula IVb, the group

may be introduced by means of an acylating agent of formula Xl

in which Hal represents a halogen atom, especially a chlorine atom.

For the introduction of a group

to give a to compound of formula IVc, a dicarboxylic acid derivative of formula XII is used

in which A and Z are as defined above, and Z preferably represents a halogen atom, especially a chlorine atom. As mentioned above, A represents the residue of a dicarboxylic acid or represents a direct bond. A is derived, for example, from malonic, dimethylmalonic, succinic, glutaric, adipic, pimelic or phthalic acid.

The compound of formula V is preferably reacted first with a base, then with carbon disulphide, and then finally with the acylating agent.

The base preferably has a pK20, and is preferably a metallated amine. Examples of preferred bases are lithium diisopropylamide, lithium 2,2,6,6-tetramethyl-piperidide, lithium cyclohexyl isopropylamide, lithium hexamethyl disilazide, and sodamide.

The reaction is generally carried out in an inert solvent, for example, an oxygenated hydrocarbon, preferably an ether, for example, diethyl ether, tetrahydrofuran, dioxane, glyme or diglyme. The reaction temperature is, for example, from -120 to +30 C, preferably from -100 to -200C.

The amount of base used is for example, from 1 to 4 moles, calculated per mole of compound V, preferably from 2.0 to 3.0 moles of base. Carbon disulphide is preferably used in amount of from 1 to 5 moles, especially from 2 to 3 moles, per mole of compound V.

The reaction is preferably carried out as follows: to a stirred solution of compound V under an inert atmosphere is added the base then carbon disulphide, if desired in solution in the same solvent as compound V or in a different solvent, and finally the acylating agent to complete the reaction.

There may then be admixed a protic source having a pK less than 10, and especially from 5 to 2, for example, acetic, citric, oxalic or formic acid.

The compound of the general formula I has R stereochemistry at position 5. This is the stereochemistry found in naturally occurring penicillins and is, in general, preferable to 5S stereochemistry, more 5R compounds being antiobiotically active than are 5S compounds.

We have found a process that gives predominantly the desired 5R compound of formula I. It has been proposed previously (British Patent Application 2074563A) to halogenate a compound of formula IV i.e., a compound having a protected hydroxy group in the side chain attached to the 3-position, but we have found that this process gives only a 4R halogenated compound, which in its turn, gives a compound analogous to that of formula I but having the undesired 5S stereochemistry. We have found that, very surprisingly, if the protective group is removed from compound IV prior to halogenation, the resulting halogenated compond of formula II is predominantly 4S.The isomer ratio 4S:4R in compound II resulting from the halogenation varies according to the reaction conditions but is, for example, in the range of from 3:1 to as high as 9:1.

Moreover, the 4R and 4S isomers of formula II can be separated easily, for example, by chromatography.

The 4S halogenated intermediates of formula II give virtually exclusively a compound of formula I with the 5R stereochemistry as shown. The presumed participation of the free hydroxyl group of the side chain of formula II in giving the more sterically hindered compound of formula I is also unexpected and constitutes a valuable advance in the preparation of the penem compounds of formula I.

The compound of formula I is itself a very useful starting material for the preparation of various derivatives substituted at position 3, especially by -SR3, wherein R3 represents alkyl having 1-10 carbon atoms or substituted alkyl; particularly a Ikyl having 1-4 C-atoms, i.e., in the synthesis of 3-substituted 7-oxo-4-thia-1 - azabicyclo[3,2,Ojhept-2-ene 2-carboxylate derivatives, that possess antibacterial properties and which are useful for the treatment of bacterial infections in humans and animals.

The following Examples illustrate the invention. In them, temperatures are given in degrees Celsius.

EXAMPLE 1 4FR)-Allylthio-3(S)-[1'(R)-{dimethyl-{2-methylprop-2-ylI-silyloxy} ethylYazetidin-2-one To a stirred solution of 1.14 ml of allyl mercaptan and 0.4 g of sodium hydroxide in 25 ml of water under an argon atmosphere was added a solution of 2.87 g of 4-acetoxy-B(S)-[l '-(R)-(dimethyl-(2-methylprop-2- yl}silyloxy} ethyl]azetid-in-2-one in 10 ml of methanol. After 30 minutes, the mixture was partitioned between dichloromethane and water. The separated organic layer was washed with water, was dried over magnesium sulphate, evaporated to dryness, and then chromatographed on silica gel. Elution with ethyl acetate / hexane mixtures afforded 1.8 g of the title compound as white crystals.

"(max)CDCl3 3420, 1767 cm~ 8 (CDCl3) 0.05 (6H,s) 0.88 (9H,s) 1.20 (3H, d, J6Hz) 2.9 - 3.2 (3H, m) 3.9-4.3 (1H, m, H-1') 3.84 (1 H, d J34 2Hz, H-4) 4.95 - 6.3 (3H, m) 7.28 (1 H, broad s) EXAMPLE 2 Methyl 2-(4(R)-allylthio-3-(S)-[1 '(R)4dimethyl-{2-methylprop-2-yl} silyloxy} ethylZazetidin-2-on- l-yl) acetate To a stirred solution of 1.76 g of 4 (R)-allylthio-3-(S)-[1'(R)-{dimethyl-{2-methylprop-2-yl}silyloxy}ethyl]aze- tidin-2-one in 60 ml of dry dimethylformamide was added 3.52 g of finely ground potassium carbonate and 0.6 ml of methyl bromoacetate.After 18 hours, the admixture was filtered and then partitioned between ethyl acetate and water. The separated organic layer was washed with water and dried over magnesium sulphate.

Evaporation in vacuo afforded a crude product which was chromatographed on silica gel. Elution with ethyl acetatelhexane mixtures afforded 1.56 g of the title compound as a pale yellow oil.

VmaxCDCl3 1753,1768 cm~ 3 (CDCl3) 0.06 (6H, s) 0.86 (9H, s) 1.23 (3H, d 6J.5Hz) 3.2 (3H, m) 3.70 (3H, s) 3.6 - 4.3 (3H, m) 4.87 (1H,dJ 2Hz, H-4) 4.9 - 6.3 (3H, m) EXAMPLE 3 4-Nitrobenzyl2-(4(R)-allylthio-3(S)-[1' '-(RJ4dimethyld2-methylprop-2-y/}silyloxy}ethylyazetidin-2-on- 1yl)acetate To a stirred solution of 3.04 g of potassium hydroxide in 80 ml of 95% ethanol was added a solution of 16 g of methyl 2- (4(R)-allylthio-3(S)-[1 '(R)-{dimethyl{2-methyl prop-2-yl} silyloxy}ethyl]azetidin-2-on-1 -yl)acetate.

After 10 minutes, the mixture was evaporated to about 1/5 of its original volume; 2 ml of dimethyl acetamide were added, followed by a solution of 9.25 g of 4-nitrobenzyl bromide in 50 ml of dimethylacetamide. After 1 hour, the mixture was partitioned between 0.01 M HCI and ethyl acetate. The separated organic layers were washed with 0.01 M HCI, with water, with cold, saturated sodium bicarbonate, and with brine, and were then dried and evaporated. The resulting crude product was chromatographed over silica gel; elution with ethyl acetate/hexane mixtures affored 19.5 g of the title compound as an oii.

vmax(cDcl3) 1755,1769cm~1 3 (CDC13) 0.07 and 0.09 (6H, two singlets) 0.88 (9H, s) 1.25 (3H, d J6Hz) 3.2 (3H, m) 3.7-4.5 (3H, m) 4.95 (1 H, d J2Hz, H-4) 4.9 - 6.3 (5H, m) 7.5 - 8.35 (4H, m) EXAMPLE 4 4-Nitrobenzyl 3,3-di(acetylthio)-[3S,4R)-4-allylthio 3-[1 '(Rl-(dimethyl-(2-methylprop-2-yl) silyloxy) ethyl azetidinon- l-yl)propenoate A solution of lithium hexamethyldisilazide was prepared by the addition of n-butyllithium in hexane (2.79 ml of a 1.6 M solution) to 0.982 ml of hexamethyldisilazane in 8 ml of drytetrahydrofuran at -10 C, while stirring under argon.The solution was cooled to -78"C and added by cannula to a solution of 0.98 g of 4-nitrobenzyl 2-(4(R)-allylthio-3(S)-[1'(R)-{dimethyl-{-methylprop-2-yl}silyloxy} ethyl]azetidin-2-on-1 -yl) acetate in 8 ml of dry tetrahydrofuran at -78 C, with stirring under argon. After 5 minutes, 0.357 ml of carbon disulphide was added by syringe, followed by 0.748 ml of acetic anhydride. The mixture was allowed to warm to room temperature, and 30 ml of dichloromethane was added, followed by 30 ml of water. The organic layer was separated, and the aqueous layer was extracted with further dichloromethane.The combined organic extracts were washed with 1 M HCI. with water, and with a 12% sodium chloride solution, and were then dried over magnesium sulphate and evaporated to give 1.38 g of an orange oil. 1.21 g of this crude product was chromatographed on silica gel using ethyl acetate/hexane mixtures as eluentto give 0.800 g of the title compound in purified form.

umax(CDCi3) 1778, 1745 cm~ 8(CDCl3) 0.06 (6H, s) 0.85 (9H, s) 1.26 (3H, d J6Hz) 2.25 (3H, s) 2.35 (3H, s) 3.11 -3.52(3H,m,3-H) 3.35 (2H, d, J 6Hz) 4.14-4.39 (1H, m) 4.95 - 6.30 (6H, m) 5.35 (2H, s) 5.56 (1 H, d J3Hz, 4-H) 7.44 - 8.38 (4H, m) EXAMPLE 5a 4-Nitrobenzyl 3,3-diRacetylthio)-2-[{3S,4R)-4-allylthiol31{ 1'RR)-hydroxyethyl-2-azetidinon- 1-yljpropenoate To a solution of 0.601 g of 4-nitrobenzyl 3,3-di-(acetylthio)-2-[(3S,4R)-4-allythio-3-(1 '(R)-{dimethyl-{2- methylprop-2-yl} silyloxy}ethyl)-2-azetidinon-1 -yl]-propenoate in 12 ml tetrahydrofuran was added a solution of 1 ml of concentrated hydrochloric acid and 1 ml of tetrahydrofuran. The solution was set aside for 24 hours and then evaporated in vacuo. Benzene was added and the mixture was evaporated to remove residual water to give 0.424 g of crude title product.A portion (0.197 g) of this crude material was chromatographed on silica gel eluting with ethyl acetate - hexane mixtures to give 0.142 g of pure title compound.

max 1774, 1738 cml (CDCl3 1.26 (3H, d, J6Hz) 2.24 (3H, s) 2.38 (3H, s) 3.35 (2H, d, J7Hz) 3.22 - 3.48 (3H, m) 3.98 - 4.45 (1 H, m) 5.30 (2H, s) 4.95-6.1 m) 7.42 - 8.23 (4H, m) EXAMPLE 5b 4-Nitrobenzyl 3,3-di(acetylthio)-2-[(3S,4R)-4-allyl-thio-3-f 1 '-hycroxyethyt\-2-azeticinon- 1-ylipropenoate To a stirred solution of 0.088 g of 4-nitrobenzyl 3,3-di-(acetylthio)-2-[(3S,4R)-4-allylthio-3-(1'(R)-{dimethyl- f2-methylprop-2-yl}silyloxy}ethyl)-2-azetidinon-1-yl]propenoate in 5 ml of acetonitrile was added 2.35 ml of concentrated (40%) hydrofluoric acid. A further volume of acetonitril (5 ml) was added after 5 minutes, and the solution was quenched with a saturated aqueous sodium bicarbonate solution.The resulting solution was extracted with dichloromethane. The resulting organic phase was washed with water, with sodium bicarbonate, and then with brine. It was then dried over MgSO4 and chromatographed on silica gel, eluting with ethyl acetatehexane mixtures to give 0.03 g of recovered starting material and then 0.0296 g of the title compound.

For spectral details see Example 5a.

EXAMPLE Sc 4-Nitrohenzyi 3,3-d;tacetylthio)-2-l{3S,4RJ-4-allylthio-34 '(R)-h ydroxyethyJ}-2-azetidin on- l-yljprop en oa te To a solution of 5.58 g of 4-nitrobenzyl 3,3-di-(acetylthio)-2-[(3S,4R)-4-allylthio3-(1'(R)-(dimethyl- {2-methylprop-2-yl} silyloxy} ethyl(-2-azetidinon-1 -ylj-propenoate in 6.5 ml of tetrahydrofuran was added a freshly prepared solution of 3.72 g of hydrogen chloride in 32 ml of tetrahydrofuran.

The solution was set aside at room temperature until the reaction was complete, and was then evaporated in vacuo. Chromatography on silica gel, eluting with ethyl acetate-hexane mixtures gave 3.10 g of the title compound.

For spectral details see Example 5a.

EXAMPLE 6a 4-Nitrob enzyl 3,3-di(acetylthio)-2-[(3S, 4S)-4-chloro-3-{ 1 '(R)-h ydroxyeth yl }-2-azetidinon-t-yljpropenoate To a solution of 0.246 g of 4-nitrobenzyl 3,3-di-(acetylthio)-2-[(3S,4R)-4-allylthio-3-(1'(R)-hydroxyethyl)-2- azetidinon-1 -yl]propenoate in 13 ml of benzene was added under an inert atmosphere 0.095 ml of t-butylhypochlorite. When the starting material had been consumed the reaction mixture was chromatorgraphed on silica gel to give as the monor product 0.045 g of 4-nitrobenzyl 3,3-di-(acetyl-thio)-2-[(3S,4R)-4chloro-3-(1 '(R)-hydroxyethyl)-2-azetidinon-1-yl]propenoate (20 %) and as the major product 0.121 g of the title compound.

For spectral details see Example 13a.

EXAMPLE 6b 4-Nitrobenzyl 3,3-di(acetylthio)-2-[(3S,4S)-4-chloro-3- ( 1 '(R(-hydroxyeth yl } -2-azetidinon- 1-ylgpropenoate To a solution of 3.10 g of 4-nitrobenzyl 3,3-di-(acetylthio)-2-[(3S,4R-4-allylthio-3-(1 '(R)-hydroxyethyl)-2azetidinon-1 -ylipropenoate in 70 ml of dry benzene cooled to 6" was added dropwise a solution of 1.5 mol equivalent of chlorine in 9.5 ml of carbon tetrachloride. When the starting material had been consumed, the solution was reduced in volume in vacuo and chromatographed on silica gel, eluting with ethyl acetate-hexane mixtures to give as the monor product 0.695 g of 4-nitrobenzyl 3,3-di-(acetylthio)-2-[(3S,4R)4-chloro-3-(1 (R)-hydroxyethyl-2-azetidinon-1 -yl]propenoate, and as the major product 1.808 g of the title compound.

For spectral details see Example 13a.

EXAMPLE 7 4-Nitrobenzyl(5R,6S) 6-{8(R)-hydroxyethyl)-7-oxo-4-thia-3-thioxo-1-azabicyclo[3,3,0]hep-2-ane 2- carboxylate To a solution of 0.525 g of 4-nitrobenzyl 3,3-di-(acetylthio)-2-[(3S,4S-4-chloro-3-(1'(R)-hydroxyethyl)-2- azetidinon-1-yl]propenoate in 15 ml of dioxan and 1.5 ml of water was added 0.227 g of imidazole. When the reaction was complete the solution was diluted with ethyl acetate and water, acidified with dilute hydrochloric acid and extracted. The aqueous phase was extracted with a second volume of ethyl acetate.

The combined ethyl acetate solution was washed with water and then with brine, dried over MgSO4 and evaporated in vacuo to give the title compound as an orange solid in quantitative yield.

vmax (liquid film) 1791,1751 cm1 3 (CDCl3) 1.39 (3H, d, J6Hz) 3.00 (1 H, s) 3.76 (1 H, 2d, J6, 4.05 - 4.53 (IH, m) 5.35 (2H, s) 5.45 H, s) 5.95 H, d, 5-H) 7.36 - 8.45 (4H, m).

EXAMPLE 8 3fS)4 {1'(R)-Dimethyl(2-methylprop-2-yl)silyloxyethyl}4(R)-ethylthioazetidin-2-one To a stirred solution of 2.03 g of sodium hydroxide in 70 ml of water at 0"C under an argon atmosphere was added 3.94 g of ethanol thiol. After 30 minutes stirring, a solution of 12.6 g of 3(S)-{1 '(R)-dimethyl(2methylprop-2-yl)silyloxy-ethyl}-4-acetoxyazetidin-2-one in 200 ml of methanol was added. The mixture was warmed to room temperature and, after 90 minutes, was partitioned between ethyl acetate and water. The aqueous layer was further washed with ethyl acetate. The combined organic layers were back-washed with brine, dried over sodium sulphate, and evaporated to dryness. 6.9 g of the title product were obtained.Yield 54% vmax (CDCI3 1765 cm~ 3 (CDCl3) 0.10 (6H, s) 0.90 (9H, s) 1.26 (3H, d, J = 6 Hz) 1.33 (3H, t, J = 7 Hz) 2.68 (2H, q, J = 7 Hz) 3.16 (1H, m) 4.1-4.3(1H, m) 4.85(1H,d,J = 2 Hz) 6.78 (1 H, broad s).

EXAMPLE 9 Methyl 2-,3(S) 1 1'(R)-(dimethyl(2-methyiprop-2-yl)silyl-oxyethyl}-4(R)-ethylthio-azetidin -2-on- 1-yl]acetate To a stirred solution of 6.9 g of 3 (S)-{1'(R)-di-methyl(2-methylprop-2-yl)silyloxyethyl}-4(R)-ethylthio- azetidin-2-one in 150 ml of dry dimethylformamide was added 13.15 g of finely ground anhydrous potassium carbonate and 2.82 ml of methyl bromoacetate. After 24 hours, the mixture was filtered and then partitioned between ethyl acetate and water. The aqueous layer was adjusted to pH 2 by dropwise addition of dilute hydrochloric acid, and then back-extracted with ethyl acetate. The combined organic layers were washed with water, dried over sodium sulphate, and evaporated in vacuo to give an orange oil, which was chromatographed over silica gel.Elution with ethyl acetate/hexane mixtures afforded 6.37 g of the title compound as a pale yellow oil.

Yield: 72 %.

Vmax (CDC13) (ester) and 1760 (p-lactam) cm~ 3 (CDCI3 0.06 (6H, s) 0.86 (9H, s) 1.3 (6H, m) 2.58 (2H, q J = 6Hz) 3.12(1H,dd,J =2Hzand4Hz 3.70 (3H, s) 3.93 (2H, dd,J gem = 17 Hz) 4.3 (1 H, m) 4.92 (1 H, d, J = 2Hz).

EXAMPLE 10 4-Nitrobenzyl 2-[3-(S)-{ 1 '(R)-dimethyl-(2-methylprop-2-yl)-silyloxyethyl}-4(R)-ethylthio-azetidin-2-on- 1-yl]- acetate To a solution of 6.37 g of methyl 2-[3(S)-{1 (R)-dimethyl(2-methylprnp-2-yl)silyloxyethyl}-4(R)-ethylthio- azetidin-2-on-1 -yl]acetate in 25 ml of 95 % ethanol was added a solution of 1.16 g of potassium hydroxide in 25 ml of 95 % ethanol. After 15 minutes, the mixture was evaporated in vacuo to dryness. The product was dissolved immediately in 25 ml of dimethylacetamide, and 4.24 g of solid 4-nitrobenzyl bromide were added with vigorous stirring. After 60 minutes, the mixture was partitioned between ethyl acetate and water.The separated aqueous layer was washed with further ethyl acetate; the combined organic layers were backwashed with water, then with brine, and were then dried over sodium sulphate and evaporated in vauo to afford an orange oil. Chromatography over silica gel, eluting with ethyl acetate/hexane mixtures afforded the title compound as a pale yellow, viscous oil. Yield: 6.18 g, 80%.

vmax (CDCl3 1765 (p-lactam) and 1755 (ester)cm~ 3 (CDCl3) 0.05 (3H, s) 0.08 (3H, s) 0.88 (9H, s) 1.25 (3H, t, J = 7Hz) 1.28 (3H, d, J = 6 Hz) 2.58 (2H, q, J = 7 Hz) 3.18(1H,dd,J '=2Hzand4Hz 4.05 (2H, dd, Jgem = 18 Hz 4.1 - 4.3 (1 H, m) 4.93(1H,d,J = 2 Hz) EXAMPLE 11 4-Nitrobenzyl 3,3-diracetylthioJ-2-[635,4R)-4ethylthio-3-f 1'(R)-{dimethy/-{2-methylprop-2-yl}silyloxy}ethyl)-2- azetidinon- I-yljpropenoate A solution of 2.0 g of 4-nitrobenzyl 2-[3S,4R)-4-ethylthio-3-(1 '(R)-{ dimethyl-{2-methylprop-2-yl}silyloxy} ethyl)-2-azetidinon-1-yl]acetate in 30 ml of dry tetrahydrofuran was held under an inert atmosphere and cooled to -78 . To the well-stirred solution was added a cooled (-78"C) preformed solution of lithium hexamethyldisilazide (prepared by addition of butyl lithium (1.55 molar, 6.01 ml, 9.31 mmol) to a tetrahydrofuran solution (20 ml) of hexamethyldisilazane (2.05 ml) cooled to - 10 ). After 5 minutes, 0.747 ml of carbon disulphide was added, followed after a further 5 minutes stirring by 1.56 ml of acetic anhydride, and the solution was warmed to -20". 80 ml of ethyl acetate was added to the solution, followed by 150 ml of dilute hydrochloric acid (0.4 molar). The aqueous layer was extracted with a further volume of ethyl acetate.

The combined ethyl acetate phase was washed with brine, then dried over magnesium sulphate and evaporated in vacuo to yield 3.03 g of the title compound, which was used subsequently without further purification.

may (CDC13 1776, 1739, 1715 cm~ 3 (CDCl3) 0.06 (6H, s) 0.85 (9H, s) 1.06 - 1.64 (6H, m) 2.10 - 3.16 (8H, m) 2.23 (3H, s) 2.35 (3H, s) 3.25 - 3.20 (1 H, m, 3-H) 4.05 - 4.67 (1 H, m) 5.34 (2H, s) 5.56 (1H, d, J4ar313 3Hz, 4-H) 7.37 - 8.44 (4H, m).

EXAMPLE 12 4-Nitrobenzyl 3,3-di(acetylthio)-2-[(3S,4R-4-ethylthio-3 1 "R)-hydroxyeth y!\-2-azetioin on- 1-yl]propenoate 0.303 g of 4-nitrobenzyl 3,3-di(acetylthio)-2-[(3S,4R)-4-ethylthio-3-(1'(R)-{dimethyl-{2-methylprnp-2-yl}- silyloxy}ethyl)-2-azetidinon-1-yl]propenoate was dissolved in a solution of 12 mol equivalent of hydrogen chloride in 5 ml of tetrahydrofu ran. The solution was stirred for 6 hours then evaporated in vacuo to 1/3 of its volume. Ethanol-free chloroform was added and the solution evaporated. The residue was chromatographed on silica gel eluting with ethyl acetate - hexane mixtures to give 0.066 g of recovered starting material and 0.1 2g of the title compound.

may 1770, 1738 cm1 3 (CDCI3) 1.03 - 1.63 (6H, m) 2.00 - 3.18 (9H, m) 3.19 - 3.48 (1H, m, 3-H) 3.95 - 4.46 (1 H, m) 5.30 (2H, s) 5.43 (1 H, d, J4a.313 3Hz, 4-H) 7.33 - 8.37 (4H, m).

EXAMPLE 13a 4Nitrobenzyl 3,3-di(acetylthio)-2-[(3S,4S)-4-chloro-3-{ I '{R)-hydroxyethyl-2-azetidinon- 1-yljpropenoate A solution of 0.10 g of 4-n itrobenzyl 3,3-di(acetylthio)-2-[(3S,4R)-4-ethylthio-3-{1'(R)-hydroxyethyl}-2- azetidinon-1 -yl]propenoate in 1.3 ml of ethanol-free chloroform was cooled to -60" under an inert atmosphere. To this solution was added a colution of chlorine in carbon tetrachloride until the starting material had been consumed. The reaction was evaporated in vacuo and chromatographed on silica gel to give 0.032 g of the title compound.

max (liquid film) 1790,1739cm1 3 (CDCl3 1.37 (3H, d, J7Hz) 2.24 (3H, s) 2.39 (3H, s) 3.58 (1 H, 2d, J3ss,O-CH-CH3 10Hz, J3P.4P 5 Hz, 3-H) 4.00 - 4.56(1 H, m) 5.30 (2H, s) 6.27 (1 H, d, 4-H) 7.38 - 8.25 (4H, m).

EXAMPLE 13b 4-Nitrobenzyl 3,3-dibacetylthio)-2-[635,4S) 4-chloro-3-[ 1 '(R)-hydroxyethyl-2-azetidinon- 1-yliprop enoate To a solution of 0.10 g of 4-nitrobenzyl 3,3-di-(acetylthio)-2-[(3S,4R) 4-ethylthio-3-[1 '(R)-hydroxyethyl-2azetidinon-1 -yl]propenoate in 2 ml of dry benzene cooled to 6" was added slowly a solution of 1.5 mole equivalent of chlorine in carbon tetrachloride until the starting material had been consumed. The solution was then chromatographed on silica gel, eluting with ethyl acetatehexane mixtures to give as a minor product 0.011 g of 4-nitrobenzyl 3,3-di(acetylthio)-2-[(3S,4R) 4-chloro-3-(1 '(R)-hydroxyethyl)-2-azetidinon-1- yl]propenoate, then as the major product, 0.065 g of the title compound.

For spectral details see Example 13a.

EXAMPLE 14 4Nitrobenzyl 3,3-diFacetylthio)-2-[r35,4R)-4chloro-3-f R){dimethyl-{2-methylprop-2-yl}silyloxy}ethyl)-2- azetidinon- 1-yUpropenoate A stirred solution of 3.519 g of 4-nitrobenzyl-3,3-di(acetylthio)-2-[(3S,4R)-4-allylthio-3-(1'(R)-{dimethyl-{2- methylprop-2-yl}silyloxy}ethyl)-2-azetidinon-1 -ylJ-propenoate in 20 ml of ethanol-free chloroform was cooled to -60". To it was added a solution of 0.48 g of chlorine in 5.6 ml of carbon tetrachloride.The resultung solution was maintained at -60" for 20 minutes, and was then warmed to room temperature, evaporated in vacuo and chromatographed on silica gel to yield 2.32 g of the title compound. mp 145-146" (from ethylacetate/hexane) vmaX (CDC13) 1795, 1743 cm~ 3 (CDCl3) 0.06 (6H, s) 0.85 (9H, s) 1.31 (3H,d,J6Hz) 2.25 (3H, s) 2.40 (3H, s) 3.53 (1 H, 2d, J33,4" 2Hz, J3ssiocH3Hzt 3-H) 4.08 - 4.50 (1 H, m) 5.37 (2H, s) 6.28 (1 H, d, 4-H) 7.45-8.42 (4H, m) EXAMPLE 15 4-Nitrohenzyl(5S, 65) 6-6(R)-{dimethyl-{2-methyl-prop-2-yl}silyloxy}ethyl)-7-oxo-4-thia-3-thioxo- 1 azabicyclo[3,2,01hept-2-ane-2-carboxylate To a stirred solution of 0.741 g of 4-nitrobenzyl 3,3-di(acetylthio)-2-[(3S,4R)4-chloro-3-(1'(R)-{dimethyl{2- methylprop-2-yl}silyloxy}ethyl-2-azetidinon-1-ylj-propenoate in 20 ml of dioxan and 2 ml of water was added 0.247 g of imidazole. After 20 minutes the solution was diluted with 120 ml of ethyl acetate and extracted with dilute hydrochloric acid, followed by brine. The organic phase was dried over MgSO4 and evaporated in vacuo to give the title compound in quantitative yield.

Vmax (liquid film) 1793,1755 cm~ 3 (CDCl3) 0.11 (6H, s) 0.89 (9H, s) 1.41 (3H,d,J6Hz) 3.96 (1 H, 2d, JspsiocH 4Hz, J63,539Hz,6-H) 4.13-4.63(1H,m) 5.25 - 5.48 (3H, m) 5.36 (2H, s) 6.05 (1 H, d, 5-H) 7.37 - 8.45 (4H, m) EXAMPLE 16 4-Nitrob enzyl 5(R),3-eth ylthio-6-(S)-{8(R)-h ydroxy-eth yJ}- 7-oxo-4-thia- 1-azabicyclo[3,2, 0Jh ep t-2-en e 2 carboxylate To a stirred solution of 0.188 g of 4-nitrobenzyl (5R,6S)-(8 (R)-hydroxyethyl)-7-oxo-4-thia-3-thioxo- - azabicyclo[3,2,0]heptane 2-carboxylate in 10 ml of dry tetrahydrofuran was added 0.094 ml of ethyl disopropylamine followed by 0.119 ml of iodoethane. When the reaction was shown to be complete (by means of thin layer chromatography) the solvent was removed in vacuo and the residue chromatographed on 10 g of silica gel (eluting with ethyl acetate-hexane) to give 0.14 g of the title compound.

EXAMPLE 17 Potassium 5(R), 3-ethylthio-6rS)-{8rR)-hydroxwethyl-}7-oxo-4thia-1-azabicyclo[3,2,0yhept-2-ene2- carboxylate To a solution of 0.139 g of 4-nitrobenzyl 5(R), (R),3-ethylthio-6(S)-{8(R)-hydroxyethyl}-7-oxo-4-thia-1 - azabicyclo [3,2,0] hept-2-ene 2-carboxylate 15 ml of ethyl acetate was added 15 ml of an aqueous solution of 0.034 g of potassium bicarbonate followed by 0.28 g of palladium on charcoal. The mixture was hydrogenated at 50 psi for one hour then filtered through 'HYFLO' which is a trade mark for a filtration aid.

The aqueous phase was extracted once with 10 ml of fresh ethyl acetate and then hydrolysed to give 0.06 g of the title compound.

EXAMPLE 18 4-Nitrobenzyl 2-r4FR)-ethylthio-3rS)-[1'{R)-dimethyl[2-methylprop-2-ylysilyloxwethyly-2-azetidinon- 1-yl)-2-{4 oxo- 1,3-dithietan-2-ylidene)acetate A solution of lithium hexamethyldisilazide was prepared by the addition of n-butyllithium in hexane (4.21 ml of a 1.6M solution) to 2.13 ml of hexamethyldisilazane in 10 ml of dry tetrahydrofuran at 0 C while stirring under nitrogen. The solution was added via a cannula to a solution of 1.08 g of 4-nitrobenzyl 2-(4(R)-ethylthio-3(S)-[1 '(R)-dimethyl-C2-methyl prop-2-yl)silyloxyethyl]-2-azetidinon-l -yl)acetate in 10 ml of dry tetrahydrofuran at -78 C, with stirring under nitrogen.After 5 minutes, 0.35 ml of carbon disu Iphide was added by syringe and after a further 90 minutes phosegene in toluene (3.56 ml of a 12.5 % solution) was added by syringe. The mixture was stirred for 90 minutes and poured into 50 ml of diethyl ether and 10 ml of 2M acetic acid. The organic layer was separated, washed with water, 12 % sodium chloride solution, dried over magnesium sulphate and evaporated to give an orange oil. Chromatography over silica gel using diethyl ether/hexane mixtures as eluent gave 0.485 g of the title compound in purified form.

Ymax (CDC13) 1770, 1760 cm~ 3(CDCl3) 0.04 (6H, s) 0.81 (9H, s) 1.18(3H,t,J = 7Hz) 1.22 (3H, d, J = 7 Hz) 2.51 (2H, q, J = 7 Hz) 3.18(1 H, dd, J = 2.7 and 3.7 Hz) 4.24(1 H, dq, J = 2.7 and 7 Hz 5.31(1 H, d, J = 2.7 Hz) 5.23, 5.45 (2H, AB, J = 13 Hz) 7.55, 8.23 (2H, A2B2, J = 9 Hz) EXAMPLE 19 4Nitrobenzyl-2- (4(Rl-ethylthio-3(Sl-[I '(RI-hydroxyethyl]-2-azefidinon- I-ylJ-2-(4-oxo- 1,3-dithietan-2- ylidene)acetate 0.30 g of 4-Nitrobenzyl 2-(4(R)-ethylthio-3(S)-[1 '(R)-dimethyl{2-methylprop-2-yl}silyloxyethyl]-2- azetidinon-1 -yl)-2-(4-oxo-1 ,3-dithietan-2-ylidene) acetate was dissolved in 4 ml of dry DMF containing a trace ofpara-quinol under a nitrogen atmosphere protected from light The solution was treated with 5 mol equivalent of hydrogen chloride in 2.2 ml of DMF. The solution was stirred for 4 hours and diluted with 5 ml of water, poured into 20 ml of dithyl ether and the organic layer separated. The aqueous portion was re-extracted with a further volume of diethyl ether and the organic fractions combined, washed with water, dried over magnesium sulphate and evaporated to give a yellow oil. Chromatography over silica gel using diethyl ether/hexane mixtures as eluant gave 0.21 g of the title compouhd in purified form.

Vmax (CDCl3) 34.50, 1785, 1760 cam~1.

8 (CDCI3) 1.13(3H,t,J = 7 Hz) 1.18(3H,d,J = 7 Hz) 2.39 (1 H, br s) 2.51 (2H, q, J = 7 Hz) 3.17(1H,dd,J = 2.7 and 3.3 Hz) 4.22(1K, m) 5.24(1H,d,J = 2.7 Hz) 5.29 (2H, s) 7.52, 8.17 (2H, A2B2, J = 9 Hz) EXAMPLE 20 4-Nitrobenzyl 2-(4(S)-chloro-3(S)-fl '(R)-h ydroxyeth yI]-2-azetidin on- 1-yI)-2-(4-oxo- 1, 3-dithietan-2- ylidene)acetate A solution of 0.208 g of 4-nitrobenzyl 2-(4(R)-ethylthio-3(S)-[1 '(R(-hydroxyethyl]-2-azetidinon-1 -yl)-2-(4- oxo-1 ,3-dithietan-2-ylidene)acetate in 1 ml of ethanol-free chloroform was cooled to -30"C under a nitrogen atmosphere and treated with 1.1 mol equivalent of chlorine in 0.82 ml of carbon tetrachloride. The reaction mixture was permitted to warm to room temperature and the solvent evaporated in vacuo. Chromatography on silica gel using diethyl ether/hexane mixtures as eluant gave 0.015 g of 4-nitrobenzyl 2-(4(R)-chloro-3 (S)[1 '(R)-hydroxyethyl]-2-azetidinon-1 -yl-2-(4-oxo-1 ,3-dithietan-2-ylidene) acetate and 0.03 g of the title compound.

Vmax (CDCL3 1775 cam~1.

8 (CDCl3) 1.45 (3H, d, J = 6.3 Hz) 3.59 (1 H, dd, J = 4.4 and 9.3. Hz) 4.37(1K, m) 5.33,5.40 (2H, AB, J = 13 Hz 6.08(1H,d,J = 4.4 Hz) 7.53, 8.27 (4H, A2B2, J = 8.6 Hz) EXAMPLE 21 4-Nitrob enzyl (5R, 6S) 6-68rR)-hydroxwethyl)-7-oXo-4thia-3-thioxo-1-azabicyclo[3,2,0shept-2-ane-2- carboxylate To a solution of 0.028 g 4-nitrobenzyl 2-(4(S)-chloro-3(S)-[1 '(R)-hydroxyethyl]-2-azetidinon-1 -yl-2-(4-oxo- 1 ,3-dithietan-2-ylidene)acetate in 1 ml of 10 % aqueous dioxane at 50C was added to trace of imidazole. When the reaction was complete the solution was diluted with diethyl ether and water, acidified with dilute hydrochloric acid and extracted. The aqueous phase was extracted with a second volume of diethyl ether and the organic portions combined, washed with water, 12 % sodium chloride solution, dried over magnesium sulphate and evaporated to give 0.01 g of crude product. Comparison of its NMR spectrum with that of the product of example 7 proved the existence of the title compound in the product mixture.

Claims

1. A compound ofthe general formula la and its tautomer Ib

in which formulae R represents a carboxyl esterifying group.

2. A compound as claimed in claim 1, wherein an esterified carboxyl group -COOR is an ester formed with an unsubstituted or substituted aliphatic, cycloaliphatic, cycloaliphatic-aliphatic, aryl, araliphatic, heterocyclic or heterocyclic-aliphatic alcohol having up to 20 carbon atoms.

3. A compound as claimed in claim 2, wherein R represents a straight or branched chain substituted or unsubstituted alkyl, alkenyl or alkynyl group having up to 18 carbon atoms.

4. A compound as claimed in claim 3, wherein a group R has up to 8 carbon atoms.

5. A compound as claimed in claim 4, wherein a group R has up to 4 carbon atoms.

6. A compound as claimed in claim 5, wherein R represents a methyl group.

7. A compound as claimed in any one of claims 2 to 6, wherein an aliphatic group R is substituted by a cycloaklyl, aryl or heterocyclic group.

8. A compound as claimed in claim 2, wherein R represents a cycloaliphatic group having up to 18 carbon atoms.

9. A compound as claimed in claim 8, wherein R represents a cyclopentyl, cyclohexyl or adamantyl group.

10. A compound as claimed in claim 2, wherein R represents an unsubstituted or substituted phenyl or aralkyl group.

11. A compound as claimed in claim 2, wherein R represents a heterocyclic group having one or more heteroatoms and up to 14 atoms in total.

12. A compound as claimed in claim 2, wherein R represents a stannyl group having up to 24 carbon atoms and three substitutents or a silyl group having up to 24 carbon atoms and up to three substitutents.

13. A compound as claimed in any one of claims 1 to 12, wherein a group R is substituted.

14. A compound as claimed in claim 13, wherein a group R is substituted by a halogen atom or a nitro group.

15. A compound as claimed in claim 1, wherein R represents a group that is removable under physiological conditions.

16. A compound as claimed in claim 15, wherein R represents an acyloxymethyl, aminoalkanyloxymethyl or optionally substituted 2-aminoethyl group.

17. A compound as claimed in claim 16, wherein R represents an L-glycyloxymethyl, L-valyloxymethyl, L-leucyloxymethyl, 2-diethylaminoethyl or 2-(1-morpholino)-ethyl ester.

18. A compound as claimed in claim 15, wherein R represents a p-nitrobenzyl, phthalidyl, pivaloyloxymethyl, acetylmethyl or acetoxymethyl group.

19. A process for the production of a compound of the general formula I, which comprises treating a compound of the general formula Ia, llb or lic

in which R is as defined in any one of claims 1 to 18, R1 represents a chlorine or bromine atom, the radicals R2a and Rub2, which may be the same or different, each represents an alkyl group having from 1 to 4 carbon atoms, an aryl group, or an aralkyl group, and A represents a direct bond or the residue of a dicarboxylic acid, with a base.

20. A process as claimed in claim 19, wherein Ra and R2b each represents a methyl or t-butyl, phenyl or benzyl group.

21. A process as claimed in claim 19 or claim 20 wherein the base is ammonia, an alkali metal alkoxide, an alkali metal carbonate, bicarbonate or hydroxide, a heterocyclic base, or a primary amine.

22. A process as claimed in claim 21, wherein a heterocyclic base has a pKa within the range of from 5 to 9.

23. A process as claimed in claim 22, wherein a heterocyclic base is imidazole.

24. A process as claimed in any one of claims 19 to 23, carried out in a solvent or diluent that is inert under the reaction conditions, or in a mixture of two or more thereof.

25. A process as claimed in claim 24, wherein a solvent mixture is a mixture of dioxan and water.

26. A process as claimed in claim 25, wherein the mixture of dioxan and water contains 5 to 10% (v/v) of water.

27. A process as claimed in any one claims 19 to 26, carried out at a temperature within the range of from 0to40"C.

28. A process as claimed in any one of claims 19 to 27, wherein a compound of formula Ila, llb or llc, respectively, is produced by halogenating a compound of the general formula Illa, Illb or Illc, respectively

in which RR2a R2b and A are defined as in claim 19, and R3 represents an alkyl group having from 1 to 8, preferably from 1 to 6, and especially from 1 to 4, carbon atoms, or an alkenyl group having up to 6 carbon atoms.

29. A process as claimed in claim 28, wherein R3 represents an ethyl or allyl group.

30. A process as claimed in claim 28 or claim 29, wherein a compound of formula Illa, Illb or Illc is halogenated with molecular chlorine, molecular bromine, sulphuryl chloride, sulphuryl bromide, t-butyl hypochlorite or cyanogen chloride.

31. A process as claimed in any one of claims 28 to 30, wherein a compound of formula Illa, IIIb or Illc is produced by removing the protective group from a compound of formula IVa, IVb or lVc, respectively,

in which R is as defined in any one of claims 1 to 18, R2a and R2 are as defined in claim 19 or claim 20, R3 is as defined in claim 28 or claim 29, and A is as defined in claim 19, and R4 denotes a hydroxy protecting group.

32. A process as claimed in claim 31, wherein a group R4 is compatible with the synthesis of compound IV and is removable under reaction conditions in which the resulting compound Ill is stable.

33. A process as claimed in claim 32, wherein R4 represents a group that is removable under acidic conditions.

34. A process as claimed in claim 33, wherein R4 represents a tetrahydrofuranyl group, or an acetal or ketal group.

35. A process as claimed in claim 34, wherein R4 represents a group of formula

in which R6 aand R7, which may be the same or different, each represents a hydrogen atom or a lower alkyl group, or R6 and R7 together with the carbon atom to which they are attached represent a ring having from 4 to 7 ring atoms; and R5 represents a lower alkyl group.

36. A process as claimed in claim 35, wherein a lower alkyl group RS or R7 is a methyl group, a ring is a tetrahydropyranyl ortetrahydrofuranyl ring, and a lower alkyl group R5 is a methyl or ethyl group.

37. A process as claimed in claim 33, wherein R4 represents a silyl group or a stannyl group as defined in claim 12.

38. A process as claimed in claim 37, wherein R4 represents a -SiR8R9R'0 group, in which R8,R9 and R10, which may be the same or different, each represents a lower alkyl group or an aryl group, or R4 represents a SnR11R12R13 group, in which R11, R12 and R13, which may be the same or different, each represents a lower alkyl group.

39. A process as claimed in claim 33, wherein R4 represents a tetrahydropyranyl, 2-methoxyprop-2-yl or t-butyldimethylsilyl group.

40. A process as claimed in any one of claims 31 to 39, wherein a compound of formula IVa, IVb or IVc is produced by treating a compound of formula V

in which R and R3 are as defined in claim 31, and R4 is as defined in any one of claims 31 to 39, with a base in the presence of carbon disulphide followed by reaction with an acylating agent, or by treatment with a base, then with carbon disulphide, and finally reaction with an acylating agent, the acylating agent comprising the appropriate group to be added to form IVa, IVb or IVc.

41. A process as claimed in claim 40, wherein the acylating agent is an acid halide, an acid anhydride or an activated ester.

42. A process as claimed in claim 40 or claim 41, wherein the acylating agent has the formula R2aOCOCOR2a R2aOCOCOR2b R20CCCOR2 RaCCZ R2COZ Hal - C - Hal or ZOC - A - COZ in which R2a and R2b are as defined in claim 19 or claim 20, Hal represents a halogen atom, especially a chlorine atom, Z represents a halogen atom, especially a chlorine atom, and A is as defined in claim 19.

43. A process as claimed in any one of claims 40 to 42, wherein the base has a pKs 20.

44. A process as claimed in any one claims 40 to 43, wherein a compound of formula V is produced by reacting a compound of formula VI

in the presence of a base, with a compound of formula IX Y1 CH2Co2R (IX) in which R is as defined in any one of claims 1 to 18 andY1 represents a group that is capable of being replaced by a nucleophilic group and is, for example, a halogen atom, preferably a bromine or iodine atom, or a modified hydroxy group, preferably a sulphonyloxy group of the formula SO3R16 represents a lower alkyl or -CF3 group, or a phenyl group which is unsubstituted or is substituted by ap-nitro,p-bromo or p-methyl group.

45. A process as claimed in claim 44, wherein Y1 represents a bromine or iodine atom, or a methylsulphonate, trifluoro-methylsulphonate, tolylsulphonate or benzenesulphonate group.

46. A process as claimed in claim 44 or claim 45, wherein a compound of formula VI is produced by reacting a compound of formula

in which R4 is as defined in any one of claims 31 to 39 with a compound of formula VIII R3-S-R14 VIII in which R3 is as defined in claim 28 or claim 29, and R14 represents a hydrogen atom or an alkali metal atom.

47. A process as claimed in claim 19, carried out substantially as described in Example 7 or Example 21 herein.

48. A process as claimed in claim 28 carried out substantially as described in any one of Examples 6, 13 and 20 herein.

49. A process as claimed in claim 31 carried out substantially as described in any one of Examples 5, 12 and 19 herein.

50. A process as claimed in claim 40 carried out substantially as described in any one of Examples 4, 11 and 18 herein.

51. A process as claimed in claim 44, carried out substantially as described in any one of Examples 2,3,9 and 10 herein.

52. A compound as claimed in claim 1, substantially as described in any one of Examples 6, 13 and 20 herein.

52. A process as claimed in claim 46, carried out substantially as described in Example 1 or Example 8 herein.

53. A compound as claimed in claim 1, whenever produced by a process as claimed in any one of claims 19 to 52 herein.

54. A compound as claimed in claim 1, substantially as described in Example 7 herein.

55. A compound of formula las claimed in any one of claims 1 to 18,53 and 54, when used for the production of a derivative thereof that is substituted atthe3-position and which retains the 5R,6Sstereochemistry, especially of a compound of the formula

in which R' represents an unsubstituted or substituted alkyl group having up to 10 carbon atoms in the alkyl group.

56. A compound ofthe general formula Ila, llb or lic

in which R, R1, R3a Rb and A are as defined in claim 31.

57. A compound of the general formula Illa, IIIb or Illc

in which R, R2a R2b, A and R3 are as defined in claim 31.

58. A compound of the general formula IVa, IVb or IVc

in which R, R2a R2b, A, R3 are as defined in claim 31 and R4 is as defined in claim 40.

59. A compound of the general formula V

in which R, R3 and R4 are as difined in claim 40.

60. A compound of the general formula VI

in which R3 and R4 are as defined in claim 40.

Amendments to the claims have been filed, and have the following effect: (a) Claims 1,2,12, and 17 to 60 above have been deleted or textually amended.

(b) New or textually amended claims have been filed as follows:

1. A compound of the general formula Ila, llb, or llc

in which R represents a carboxyl esterifying group, R' represents a chlorine or bromine atom, the radicals Ra and Rb, which may be the same or different, each represents an alkyl group having from 1 to 4 carbon atoms, an aryl group, or an aralkyl group, and A represents a direct bond or the residue of a dicarboxylic acid.

2. A compound as claimed in claim 1, wherein an esterified carboxyl group -COOR is an ester formed with an unsubstituted or substituted aliphatic, cycloaliphatilc, aryl, or heterocyclic alcohol having

12. A compound as claimed in claim 1, wherein R represents a stannyl group having up to 24 carbon atoms and three substituents or a silyl group having up to 24 carbon atoms and up to three substituents.

17. A compound as claimed in claim 16, wherein R represents an L-glycloxymethyl, L-valinyloxymethyl, L-leucyloxymethyl, 2-diethylaminoethyl or 2-(1 -morpholino)-ethyl ester.

18. A compound as claimed in claim 15, wherein R represents a p- nitrobenzyl, phthalidyl, pivaloyoxymethyl, acetylmethyl or acetoxymethyl group.

19. A compound as claimed in any one of claims 1-18, wherein R2a and R2b each represents a methyl or t -butyl, phenyl or benzyl group.

20. A process for the production of a compound of formula Ila, llb, or llc, which comprises halogenating a compound of the general formula Illa, Illb or Illc, respectively

in which R, R3a and R2b and A are defined as in claim 1, and R3 represents an alkyl group having from 1 to 8 carbon atoms, or an alkenyl group having up to 6 carbon atoms.

21. A process as claimed in claim 20, wherein R3 represents an ethyl or allyl group.

22. A process as claimed in claim 20 or claim 21, wherein a compound of formula Illa, Illb or Illc is halogenated with molecular chlorine, molecular bromine, sulphuryl chloride, sulphuryl bromide, t- butyl hypochlorite or cyanogen chloride.

23. A compound of formula Illa, Illb, or Illc as defined in claim 22.

24. A process for the production of a compound of formula Illa, Illb or Illc as claimed in claim 23, which comprises removing the protective group from a compound of formula IVa, IVb or IVc, respectively,

in which R is defined in any one of claims 1 to 18, Ra2 and R2b are as defined in claim 1 or claim 19, R3 is as defined in claim 20 or claim 21, A is as defined in claim 1, and R4 denotes a hydroxy protecting group.

25. A process as claimed in claim 24, wherein a group R4is compatible with the synthesis of compound IV and is removable under reaction conditions in which the resulting compound Ill is stable.

26. A process as claimed in claim 25, wherein R4 represents a group that is removable under acidic conditions.

27. A process as claimed in claim 26, wherein R4 represents a tetrahydrofuranyl group, or an acetal or ketal group.

28. A process as claimed in claim 27, wherein R4 represents a group of formula

in which R6 and R7, which may be the same or different, each represents a hydrogen atom or a lower alkyl group, or R6 and R7 together with the carbon atom to which they are attached represent a ring having from 4 to 7 ring atoms; and R5 represents a lower alkyl group.

29. A process as claimed in claim 28, wherein a lower alkyl group R6 or R7 is a methyl group, a ring is a tetrahydropyranyl or tetrahydrofuranyl ring, and a lower alkyl group R5 is a methyl or ethyl group.

30. A process as claimed in claim 26, wherein R4 represents a silyl group or a stannyl group as defined in claim 12.

31. A process as claimed in claim 30, wherein R4 represents a -SiR8R9R10 group, in which R8, R9 and R10, which may be the same or different, each represents a lower alkyl group or an aryl group, or R4 represents a SnR1lRl2Rl3 group, in which R11, R12 and R13, which may be the same of different, each represents a lower alkyl group.

32. A process as claimed in claim 26, wherein R4 represents a tetrahydropyranyl, 2-methoxyprop-2-yl or t-butyldimethylsilyl group.

33. A process as claimed in any one of claims 24 to 32, wherein a compound of formula IVa, IVb or IVc is produced by treating a compound of formula V

in which R and R3 are as defined in claim 24, and R4 is as defined in any one of claims 24 to 32, with a base in the presence of carbon disulphide followed by reaction with an acylating agent, or by treatment with a base, then with carbon disulphide, and finally reaction with an acylating agent, the acylating agent comprising the appropriate group to be added to form compound IVa, IVb or IVc.

34. A process as claimed in claim 33, wherein the acylating agent is an acid halide, an acid anhydride or an activated ester.

35. A process as claimed in claim 33 or claim 34, wherein the acylating agent has the formula R2a OCOCORa R2a OCOCOR3b R2b OCOCOR2b R2a COZ R2bCOZ

in which R2a and R2b are as defined in claim 1 or claim 19, Hal represents a halogen atom, Z represents a halogen atom, and A is as defined in claim 1.

36. A process as claimed in claim 35, wherein a halogen atom is a chlorine atom.

37. A process as claimed in any one of claims 33 to 36, wherein the base has a pom20.

38. A process as claimed in any one of claims 33 to 37, wherein a compound of formula V is produced by reacting a compound of formula VI

in the presence of a base, with a compound of formula IX Y1 CH2CO2R (IX) in which R is as defined in any one of claims 1 to 18 andY1 represents a group that is capable of being replaced by a nucleophilic group.

39. A process as claimed in claim 38, wherein Y1 represents a halogen atom or a modified hydroxy group.

40. A process as claimed in claim 39, wherein Y1 represents a sulphonyloxy group of the formula S03R16 in which R16 represents a lower alkyl or CF3 group, or a phenyl group, or a phenyl group which is unsubstituted or is substituted by a p-nitro p - bromo orp -methyl group.

41. A process as claimed in claim 39, wherein Y1 represents a bromine or iodine atom, or a methylsulphonate, trifluoromethylsulphonate, tolylsulphonate or benzenesulphonate group.

42. A process as claimed in any one of claims 38 to 41, wherein a compound of formula IV is produced by reacting a compound of formula VII.

in which R4 is as defined in any one of claims 24 to 32, with a compound of formula VIII R3 - S - R14 (veil) in which R3 is as defined in claim 20 or claim 21, and R14 represents a hydrogen atom or an alkali metal atom.

43. A process as claimed in claim 20, carried out substantially as described in any one of Examples 6, 13 and 20 herein.

44. A process as claimed in claim 24, carried out substantially as described in any one of Exampless 5, 12 and 19 herein.

45. A process as claimed in claim 33, wherein a compound of formula IVa, IVb, or IVc is produced substantially as described in any one of Examples 4,11 and 18 herein.

46. A process as claimed in claim 38, wherein a compound of formula V is produced substantially as described in any one of Examples 2,3,9 and 10 herein.

47. A process as claimed in claim 42, wherein a compound of formula VI is produced substantially as described in Example 1 or Example 8 herein.

48. A compound of formula Illa, Illb or Illc, whenever produced by a process as claimed in any one of claims 24 to 42 and 44 to 47.

49. A compound of formula Illa, Illb or Illc, substantially as described in any one of Examples 5, 12 and 19 herein.

50. A process as claimed in claim 20, wherein the compound of formula Illa, Illb or Illc is as claimed in claim 48 or claim 49.

51. A compound as claimed in claim 1, whenever produced by a process as claimed in any one of claims 20 to 22 or claim 50.