GB2031871A - Process for the production of 2- (2',2',2'-tribromoethyl)-4- chlorocyclobutan-1-ones - Google Patents

Abstract

2-(2',2',2'-Tribromoethyl)-4- chlorocyclobutan-1-ones of the formula I <IMAGE> in which one of the radicals R1 and R2 is methyl and the other is hydrogen or methyl, or R1 and R2 together are an alkylene group having 2 to 4 carbon atoms are prepared by reacting the novel 2-chloro-4,4,4-tribromobutyric acid chloride, in the presence of an organic base, with an ethylene, which is disubstituted in the 1-position by the radicals R1 and R2 according to the above definition, to give a 2-(2',2',2'- tribromethyl)-2-chlorocyclobutan-1- one, and then rearranging this, in the presence of a catalyst, into a 2-(2',2',2'- tribromoethyl)-4-chlorocyclobutan-1- one of the formula I. The 2-(2',2',2'- tribromoethyl)-4-chlorocyclobutan-1- ones of the formula I are valuable intermediates for the preparation of 2-(2',2'-dibromovinyl)-cyclopropane-1- carboxylic acids and esters thereof having an insecticidal action.

Description

SPECIFICATION Process for the production of 2-(2',2',2'4ribromoethyl)-4-chlorncyclobutan-1 -ones The present invention relates to a process for the preparation of 2-(2',2',2'-tribromoethyl )-4- chlorocyclobutan-1-ones of the formula I

in which one of the radicals R1 and R2 is methyl and the other is hydrogen or methyl, or R1 and R2 together are an alkylene group having 2 to 4 carbon atoms.

The present invention relates also to the novel 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1-ones of the formula I which can be prepared by the process according to the invention, and also to novel intermediates which can be used for their preparation.

The 2-(2',2',2-'-tribrnmoethyl)-4-chlorncyclobutan-1 -ones of the formula I are valuable intermediates which can be converted by heating with bases, such as alkali metal hydroxides and alkali metal alcoholates, in a known manner (Favorski reaction) into cyclopropane-carboxylic acids or into esters thereof, which in their turn are converted on further reaction with suitable alcohols, for example m-phenoxy-a-cyanobenzyl alcohol, into esters having an insecticidal action. Cyclopropane-carboxylic acid esters (pyrethroids) of this kind having an insecticidal action are described for example in the German Offenlegungsschriften 2,326,077 and 2,439,177.

It has now been found that 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1-ones of the formula I can be produced in a simple manner by reacting 2-chloro-4,4,4-tribromobutyric acid chloride of the formula II

in the presence of an organic base, with an olefine of the formula ill

in which R1 and R2 have the meanings defined under the formula I, to give a 2-(2',2',2'-tribromoethyl)-2chlorocyclobutan-1-one of the formula IV

in which R1 and R2 have the meanings defined under the formula I, and subsequently rearranging this, in the presence of a catalyst, into a 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1 -one of the formula The 2-chloro-4,4,4-tribromobutyric acid chloride of the formula II is a novel compound.It can be prepared by firstly converting 4,4,4-tribromobutyric acid, by reaction with an inorganic acid chloride, into 4,4,4-tribromobutyric acid chloride, and then chlorinating this in the a-position.

The 4,4,4-tribromobutyric acid required as starting material can be obtained by reaction of bromoform with acrylonitrile, and subsequent hydrolysis of the formed 4,4,4-tribromobutyric acid nitrile (J. Amer. Chem.

Soc. 67, 601-602 (1945)).

The inorganic acid chlorides used can be phosphorus trichloride, phosphorus oxychloride, phosgene, thionyl chloride and oxalyl chloride. The reaction of 4,4,4-tribromobutyric acid with the inorganic acid chloride is advantageously performed in the presence of a catalytic amount of dimethyl formamide. Excess inorganic acid chloride can serve as the solvent.

The chlorination of 4,4,4-tribromobutyric acid chloride in the 2-position is performed in the customary manner. The chlorinating agent employed can be for example free chlorine or N-chlorosuccinimide. A preferred chlorinating agent is N-chlorosuccinimide. Chlorination can be performed, without isolation of the 4,4,4-tribromobutyric acid chloride, immediately after the reaction of the 4,4,4-tribromobutyric acid with the inorganic acid chloride, in excess inorganic acid chloride as solvent. A purer product is obtained however if the 4,4,4-tribromobutyric acid chloride is isolated, and the subsequent chlorination is carried out separately.

Chlorination is performed at temperatures of 40 to 90"C, preferably at 60 to 70 C. It is advantageous to expose the reaction mixture to UV light during chlorination, orto add some known radical starters, for example dibenzoyl peroxide or azobisisobutyronitrile.

The reaction of the 2-chloro-4,4,4-tribromobutyric acid chloride of the formula II with olefines of the formula Ill is advantageously carried out in the presence of an inert organic solvent. Suitable solvents are, for example, aromatic or aliphatic hydrocarbons, which can be halogenated, such as benzene, toluene, xylenes, chlorobenzene, dichloro- and trichloro-benzenes, n-pentane, n-hexane, n-octane, methylene chloride, chloroform, carbon tetrachloride, 1,1 ,2,2-tetrachloroethane and trichloroethylene. Further suitable solvents are cycloaliphatic hydrocarbons such as cyclopentane or cyclohexane, cycloaliphatic ketones such as cyclopentanone and cyclohexanone, and also aliphatic ketones, aliphatic and cyclic ethers, alkylnitriles and 3-alkoxypropionitriles having 1 or 2 carbon atoms in the alkoxy group, especially acetonitrile and 3-methoxypropionitrile.

Preferably suitable solvents are aliphatic, cycloaliphatic and aromatic hydrocarbons, in particular alkanes having 5 to 8 carbon atoms, benzene and toluene, and especially n-hexane and cyclohexane.

However, excess olefine of the formula III can also serve as the solvent.

Suitable organic bases, in the presence of which the reaction of the 2-chloro-4,4,4-tribromobutyric acid chloride of the formula II with an olefine of the formula lil is carried out, are, for example tertiary amines, in particular trialkylamines having 1 to 4 carbon atoms, and especially 2 to 4 carbon atoms, in each alkyl group, cyclic amines, such as pyridine, quinoline, and N-alkyl-pyrrolidines, N-alkyl-piperidines, N,N-dialkylpiperazines and N-alkyl-morpholines or dialkylanilines having 1 or 2 carbon atoms in each alkyl group, such as N-methyl-pyrrolidine, N-ethyl-piperidine, N,N'-dimethyl-piperazine, N-ethyl-morpholine and N,Ndimethylaniline, and also bicyclic amidines, such as 1 ,5-diazabicyclo [5.4.0] undec-5-ene and 1,5diazabicyclo [4.3.0] non-5-ene, and bicyclic diamines, such as 1A-diazabicyclo [2.2.2] octane.

The reaction of the 2-chloro-4,4,4-tribromobutyric acid chloride of the formula II with olefines of the formula Ill is preferably carried out in the presence of trialkylamines having 1 to 4 carbon atoms in each alkyl group. Particularly suitable bases are triethylamine and pyridine.

The organic base is employed in at least the equimolar amount, or in a slight excess, based on the 2-chloro-4,4,4-tribromobutyric acid chloride of the formula II.

The olefines of the formula Ill are likewise used in at least the equimolar amount, based on the 2-chloro-4,4,4-tribromobutyric acid chloride of the formula II. It is, however, generally advantageous to use an excess of the olefine, in which case the olefine can, as already mentioned, also serve as the solvent. When readily volatile olefines are used, the reaction can be carried out under pressure.

The olefines of the formula III are in particular those in which one of the radicals R, and R2 is methyl and the other is hydrogen or methyl, or R1 and R2 together are an alkylene group having 2 to 3 carbon atoms, i.e.

isobutylene, propene, methylenecyclopropane and methylenecyclobutane. Isobutylene and methylenecyclopropane are particularly preferred.

The reaction temperatures can vary within wide limits. They are in general between 0 and 200 C and preferably between 20 and 160 C.

The 2-(2',2',2'-tribromoethyl)-2-chlorocyclobutan-1-ones of the formula IV are also novel compounds.

Catalysts which can be used for the rearrangement of the 2-(2',2',2'-tribromoethyl)-2-chlorocyclobutan-1- ones of the formula IV, which are first obtained, into 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1 -ones of the formula I are acids, bases or quaternary ammonium halides.

The rearrangement, according to the invention, of 2-(2',2',2'-tribromoethyl)-2-chlorocyclobutan-1 -ones of the formula IV into 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1-ones of the formula I is unexpected and is not known in the case of cyclobutanones monohalogenated in the a-position. The rearrangement proceeds with excellent, and frequently quantitative, yield.

The rearrangement, according to the invention, of 2-(2',2',2'-tribromoethyl)-2-chlorocyclobutan-1 -ones of the formula IV into 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1-ones of the formula I is preferably carried out in the presence of basic catalysts. The basic catalysts are organic bases, such as primary, secondary and especially tertiary amines of the formula

in which Q is alkyl having 1 to 8 carbon atoms, cycloalkyl having 5 to 6 carbon atoms, benzyl or phenyl and Q2 and Q3 independently of one another are hydrogen or alkyl having 1 to 8 carbon atoms.Suitable basic catalysts are, for example, triethylamine, tri-n-butylamine, tri-iso-pentylamine, tri-n-octylamine, N,Ndimethylcyclohexylamine, N,N-dimethylbenzvlamine, N,N-dimethyl-2-ethylhexylamine, N,N-diethylaniline and also cyclic amines, such as pyridine, quinoline, lutidine, N-alkylmorpholines, such as N-methylmorpholines, N-alkyl-piperidines, such as N-methyl- and N-ethyl-piperidine, N-alkyl-pyrrolidines, such as N-methyl- and N-ethyl-pyrrolidine, diamines, such as N,N,N',N'-tetramethylethylenediamine and N,N,N',N'tetramethyl-1,3-diaminobutane, N,N'-dialkylpiperazines, such as N,N'-dimethylpiperazine, bicyclic amines, such as 1,4-diazabicyclo [2.2.2] octane, and bicyclic amidines, such as 1,5-diazabicyclo [5.4.01 undec-5-ene and 1,5-diazabicyclo-[4.3.0] non-5-ene, and finally polymeric basic compounds, such as pdimethylaminomethylstyrene.

Further suitable basic catalysts for the rearrangement, according to the invention, of a 2-(2',2',2' tribromoethyl)-2-chlorocyclobutan-1 -one of the formula IV into a 2-(2',2',2'-tribromoethyl)-4 chlorocyclobutan-1-one of the formula I are phosphines, especially trialkylphosphines, for example tributylphosphine.

Acid catalysts which can be used for the rearrangement of 2-(2',2',2'-tribromoethyl)-2-chlorocyclobutan-1 ones of the formula IV into 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1 -ones of the formula I are inorganic or organic proton acids. Suitable inorganic proton acids are, for example, hydrogen halide acids, such as hydrogen chloride, hydrogen bromide, hydrogen fluoride and hydrogen iodide, nitric acid, phosphoric acid and sulphuric acid. Preferred inorganic proton acids are hydrogen halide acids.

If acids or bases are employed in excess, they can also serve as solvents.

Furthermore, salts of proton acids, especially hydrogen halide acids, with ammonia or a nitrogencontaining organic base, and also quaternary ammonium halides, quaternary phosphonium halides and sulphonium halides can be employed. Suitable nitrogen-containing organic bases are aliphatic, cycloaliphatic, araliphatic and aromatic primary, secondary and tertiary amines, as well as heterocyclic nitrogen bases.

Examples are: primary aliphatic amines having up to 12 C atoms, such as methylamine, ethylamine, n-butylamine, n-octylamine, n-dodecylamine, hexamethylenediamine, cyclohexylamine and benzylamine; secondary aliphatic amines having up to 12 C atoms, such as dimethylamine, diethylamine, di-npropylamine, dicyclohexylamine, pyrrolidine, piperidine, piperazine and morpholine; tertiary aliphatic amines, especially trialkylamines having 1-4 C atoms in each alkyl moiety, such as triethylamine, tri-n-butylamine, N-methylpyrrolidine, N-methylmorpholine, 1,4-diazabicyclo [2.2.2] octane and quinuclidine; substituted or unsubstituted primary, secondary and tertiary aromatic amines, such as aniline, toluidine, naphthylamine, N-methylaniline, diphenylamine and N,N-diethylaniline; and also pyridine, picoiine, indoline and quinoline.

Quaternary phosphonium halides which can be used are, for example; hexadecyltributylphosphonium bromide and methyl- and ethyl-triphenylphosphonium bromide; and a sulphonium halide which can be used is, for example, trimethylsulphonium iodide.

Preferred salts are those of the formula

in which M is fluorine, bromine or iodine and especially chlorine, Q4 is hydrogen, alkyl having 1-18 C atoms, cyclohexyl, benzyl, phenyl or naphthyi and Q5, Qe and Q7 independently of one another are hydrogen or alkyl having 1-18 C atoms, and also N-alkyl-pyridinium halides having 1-18 C atoms in the alkyl, especially the corresponding chlorides.

Examples of such salts are: ammonium chloride, ammonium bromide, methylamine hydrochloride, cyclohexylamine hydrochloride, aniline hydrochloride, dimethylamine hydrochloride, di-isobutylamine hydrochloride, triethylam ine hydrochloride, triethylam ine hydrobromide, tri-n-octylamine hydrochloride, benzyl-dimethylamine hydrochloride, tetramethylammonium chloride, bromide and iodide, tetraethylammonium chloride, bromide and iodide, tetra-n-propylammonium chloride, bromide and iodide, tetra-nbutylammonium chloride, bromide and iodide, trimethyl-hexadecylammonium chloride, benzyldimethylhexadecylammonium chloride, benzyldimethyltetradecylammonium chloride, benzyl-trimethyl-, -triethyl- and -tri-n-butyl-ammonium chloride, n-butyl-tri-n-propylammonium bromide, octadecyltrimethylammonium bromide, phenyltrimethylammonium bromide or chloride and hexadecylpyridinium bromide and chloride.

Additional co-catalysts which can be used are alkali metal halides, such as potassium iodide, sodium iodide, lithium iodide, potassium bromide, sodium bromide, lithium bromide, potassium chloride, sodium chloride, lithium chloride, potassium fluoride, sodium fluoride and lithium fluoride.

These co-catalysts catalyse the reaction even in the absence of the above ammonium salts, but additions of open-chain or macrocyclic polyethers (crown ethers) are then advantageous for a rapid course of reaction.

Examples of such crown ethers are: 15-crown-5, 18-crown-6, dibenzo-1 8-crown-6, dicyclohexyl-18-crown-6 and 5,6,14,1 5-dibenzo-7,1 3-diaza-1 ,4-dioxa-cyclopentadeca-5,1 4-diene.

The amount of catalyst employed can vary within wide limits. In some cases it suffices if the catalyst is present in traces. In general, however, the catalyst is preferably employed in an amount of about 0.1 to 15 per cent by weight, based on the compound of the formula VI.

The rearrangement can be carried out either in the melt or in an inert organic solvent. The reaction temperatures for the rearrangement in the melt are in general between about 60 and 1 50"C and especially about 80 to 1 30 C.

Suitable catalysts for the rearrangement in the melt are, in particular, the abovementioned organic bases, especially trialkylamines having 1-8 C atoms in each alkyl moiety; and also salts of hydrogen halide acids with ammonia or organic nitrogen-containing bases, such as trialkylamine hydrochlorides having 1 - 8 C atoms in each alkyl moiety, and very particularlytetraalkylammonium halides, in particular tetraalkylammonium chlorides, bromides and iodides, having 1-18 C atoms in each alkyl moiety.

Examples of suitable inert organic solvents are aliphatic, cycloaliphatic or aromatic hydrocarbons, which can be nitrated or halogenated, such as n-hexane, n-pentane, cyclohexane, benzene, toluene, xylenes, nitrobenzene, chloroform, carbon tetrachloride, trichloroethylene, 1,1 ,2,2-tetrachloroethane, nitromethane, chlorobenzene, dichlorobenzenes and trichlorobenzenes; lower aliphatic alcohols, for example those having up to 6 C atoms, such as methanol, ethanol, propanol, isopropanol, butanols and pentanols; aliphatic diols, such as ethylene glycol and diethylene glycol; ethylene glycol monoalkyl ethers and diethylene glycol monoalkyl ethers having, in each case, 1-4 C atoms in the alkyl moieties, such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether, diethylene glycol monomethyl ether and diethylene glycol monoethyl ether; cyclic amides, such as N-methyl-2-pyrrolidone, N-acetyl-2-pyrrolidone and N-meThyl-e-caprnlactam; amides of carbonic acid, such as tetramethylurea and dimorpholinocarbonyl; amides of phosphorous acid, of phosphoric acid, of phenylphosphonic acid or of aliphatic phosphonic acids having 1-3 C atoms in the acid moiety, such as phosphoric acid triamide, phosphoric acid tris (dimethylamide), phosphoric acid trimorpholide, phosphoric acid tripyrrolinide, phosphoric acid bis (dimethylamide)-morpholide, phosphoric acid dimethylamide-diethylamide-morpholide, phosphorous acid tris-(dimethylamide) and the tetramethyldiamide of methanephosphonic acid; amides of sulphuric acid and of aliphatic or aromatic sulphonic acids, such as tetramethylsulphamide, the dimethylamide of methanesulphonic acid or p-toluenesulphonic acid amide; sulphur-containing solvents, such as organic sulphones and sulphoxides, for example dimethylsulphoxide and sulpholane; and aliphatic and aromatic nitriles, 3-alkoxypropionitriles, aliphatic ketones, alkyl and alkoxyalkyl esters of aliphatic monocarboxylic acids, cyclic ethers, dialkyl ethers, N,N-distributed amides of aliphatic monocarboxylic acids and ethylene glycol dialkyl ethers and diethylene glycol dialkyl ethers of the type mentioned under process stage 1).

For the rearrangement in the presence of an acid catalyst, polar solvents are advantageously used, especially lower alcohols, such as methanol, ethanol and butanols, N,N-dialkylamides of aliphatic monocarboxylic acids having 1-3 C atoms in the acid moiety, especially N,N-dimethylformamide, or dialkylsulphoxides, such as dimethylsulphoxide.

In aprotic, strongly polar solvents, such as the above-mentioned N,N-disubstituted amides of aliphatic monocarboxylic acids, cyclic am ides, amides of carbonic acid, amides of phosphorous acid, of phosphoric acid, of phenylphosphonic acid or of aliphatic phosphonic acids, amides of sulphuric acid or of aliphatic or aromatic sulphonic acids, and also dialkylsulphoxides, such as dimethylsulphoxide, the reaction also proceeds without the addition of base or acid. In these cases, the solvent acts as the catalyst.

In general, however, when the rearrangement is carried out in the presence of an inert organic solvent a catalyst is added, preferably an organic base having a pKa vaiue of more than 9, especially trialkylamines having 1-8 C atoms in each alkyl moiety, such as triethylamine, tri-n-butylamine and tri-n-octylamine; and also hydrogen halide acids, especially HCI and HBr, and tetraalkylammonium halides, especially tetraalkylammonium chlorides, bromides and iodides having 1-18 C atoms in each alkyl moiety.

Particularly preferred solvents are aliphatic alcohols having 1-4 C atoms, toluene, xylenes, chlorobenzene, dioxane, acetonitrile, 3-methoxypropionitrile, ethylene glycol di-ethyl ether and di-isopropyl ketone.

The reaction temperatures for the rearrangement in the presence of an inert organic solvent are in general between about 0 and 150 C and preferably between about 80 and 130 C.

By means of the process according to the invention, novel 2-(2',2',2'-tribromoethyl)-4-chloro-cyclobutan- 1-ones of the formula I, which are substituted in the 3-position and are suitable as intermediates for the preparation of 2-(2',2'-dibromovinyl)-cyclopropanecarboxylic acid derivatives substituted in the 3-position, are available in a simple manner and in good yield, using readily accessible starting materials.The course of the process according to the invention is extremely surprising and completely unforeseeable, since, when the 2-chloro-4,4,4-tribromobutyric acid chloride of the formula II, or a chloroketene formed therefrom in situ by the elimination of hydrogen chloride, is reacted with an olefine of the formula Ill, a 2-(2',2',2'tribromoethyl)-2-chlorocyclobutan-1 -one of the formula IV, which is unsuitable for further conversion into a 2-(2',2'-dibromovinyl)-cyclopropanecarboxylic acid derivative substituted in the 3-position, is first formed and this is then converted, by a novel rearrangement, not hitherto observed in the case of cyclobutanones, monohalogenated in the a-position, into a 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1-one of the formula I, which is suitable for further conversion into a 2-(2',2'-dibromovinyl)-cyclopropanecarboxylic acid derivative substituted in the 3-position.

The 2-(2',2'-dibromovinyl)-cyclopropanecarboxylic acids substituted in the 3-position, and their esters having an insecticidal action, which can be prepared using novel 2-(2',2',2'-tribromoethyl)-4 chlorocyclobutan-1-ones of the formula I as the starting materials, can be described by the following formula VIII::

in which R1 and R2 are as defined under formula I and R is hydrogen, alkyl having 1 to 4 carbon atoms or a group of the formula IX

in which R3 is oxygen, sulphur or a vinylene group, R4 is hydrogen, alkyl having 1 to 4 carbon atoms, benzyl, phenoxy or phenylmercapto, R5 is hydrogen or an alkyl group having 1 to 4 carbon atoms and R6 is hydrogen, cyano or ethynyl, or, if one of the radicals R1 and R2 is methyl and the other is hydrogen or methyl, R3 is the vinylene group, Ra is phenoxy and R5 is hydrogen, also alkyl having 1 to 5 carbon atoms.

The 2-(2',2'-dibromovinyl)-cycloperopanecarboxylic acid derivatives of the formula Vlil in which R is a group of the formula IX are suitable for combating diverse animal or plant pests, especially insects. The properties, fields of application and use forms of these active compounds are described in the literature (c.f., for example, Nature, 246, 169-170 (1973); Nature, 248,710-711(1974); Proceedings 7th British Insecticide and Fungicide Conference, 721-728(1973); Proceedings 8th British Insecticide and Fungicide Conference, 373-78 (1975); J. Agr. Food Chem. 23, 115 (1973); U.S. Patent Specification 3,961,070; and German Offenlegungssch riften 2,553,991, 2,439,177, 2,326,077 and 2,614,648).

The conversion of 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1 -ones of the formula I into 2-(2',2' dibromovinyl)-cyclopropanecarboxylic acid derivatives of the formula VIII is carried out in a manner known per se, by heating in the presence of suitable bases. Examples of suitable bases are alkali metal hydroxides and alkaline earth metal hydroxides, such as sodium hydroxide, potassium hydroxide, calcium hydroxide and barium hydroxide. Alkali metal carbonates and bicarbonates and alkaline earth metal carbonates and bicarbonates, such as calcium carbonate, barium carbonate, potassium carbonate, sodium carbonate, sodium bicarbonate and potassium bicarbonate, can also be used as bases.Further suitable bases are alcoholates derived from the radical R according to the above definition, especially the corresponding sodium alcoholates and potassium alcoholates. The use of such alcoholates has the advantage that the corresponding ester is obtained direct, whilst when alkali metal hydroxides and alkaline earth metal hydroxides are used, the salts of these bases with the 2-(2',2'-dibromovinyl)-cyclopropanecarboxylic acid formed are first obtained. These salts can, however, also be converted into esters in a simple manner which is known per se, for example by converting them into the corresponding acid chloride and reacting the latter with an alcohol derived from the radical R.

Depending on the nature of the base used, the conversion of a 2-(2',2',2'-tribromoethyl)-4chlorocyclobutan-1 -one of the formula I into a 2-(2',2'-dibromovinyl)-cyclopropanecarboxylic acid derivative of the formula VIII is advantageously carried out in an aqueous, aqueous-organic or organic medium. When the base used is an alkali metal carbonate or alkaline earth metal carbonate, the reaction is carried out in an aqueous or aqueous-organic medium. The reaction in the presence of alkali metal hydroxides or alkaline earth metal hydroxides and alkali metal bicarbonates is also advantageously carried out in an aqueous or aqueous-organic medium. In this case, the free 2-(2',2'-dibromovinyl)-cyclopropanecarboxylic acids of the formula VIII (R = H) are obtained after acidifying the reaction mixture, for example by adding concentrated hydrochloric acid.

Suitable solvents for the conversion of 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1 -ones of the formula I into 2-(2',2'-dibromovinyl)-cyclopropanecarboxylic acid derivatives of the formula VIII in an aqueousorganic or organic medium are lower alcohols, for example those having 1 to 6 carbon atoms, benzyl alcohol, aliphatic or cyclic ethers, such as diethyl ether, di-n-propyl ether, diisopropyl ether, tetrahydrofurane and dioxane, and also aliphatic, cycloaliphatic or aromatic hydrocarbons, such as n-pentane, n-hexane, cyclohexane, benzene, toluene and xylenes.

The conversion of 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1-ones of the formula I to 2-(2',2'dibromovinyl)-cyclopropanecarboxylic acid derivatives of the formula VIII is generally carried out at the boiling point of the reaction medium chosen. Reaction temperatures of between 40 and 120 C are particularly suitable.

When 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1-ones of the formula I are converted into 2-(2',2' dibromovinyl)-cyclopropanecarboxylic acid derivatives of the formula VIII, the corresponding 2-(2',2',2'tribromoethyl)-cyclopropanecarboxylic acid derivatives of the formula X

in which R, R1 and R2 are as defined, are formed as intermediates. These products can be isolated if the reaction temperature is kept below 40"C and/or a less than equivalent amount of base is used. Above 40 C, these intermediates are converted to the corresponding 2-(2',2'-dibromovinyl)-cyclopropanecarboxylic acid derivatives of the formula VIII on the addition of further base, with the elimination of HX.

The 2-(2',2',2'-tribromoethyl)-cyclopropanecarboxylic acid derivatives of the formula X can also be prepared photochemicallyfrom 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1 -ones of the formula I, by irradiation with UV light, if necessary with the addition of conventional sensitisers (for example ketones, such as acetone, cyclohexanone, benzophenone, acetophenone and higher alkylaryl ketones, thioxanthone and the like), in the presence of reagents containing hydroxyl groups, which at the same time can serve as solvents. Examples of reagents containing hydroxy groups are alkanols, such as methanol, ethanol and the like, and in particular water.

The process according to the invention is illustrated in more detail by the following examples.

Example a) Preparation of 4,4,4tribromobutyric acid chloride 324.8 g (1.0 mol) of 4,4,4-tribromobutyric acid, 600 g of thionyl chloride and 1 ml of dimethyl formamide are heated firstly for 2 hours at 40 C and then for 3 hours at 75 C. The excess thionyl chloride is afterwards distilled off, and the residue is rectified under high vacuum. The yield is 326.0 g (95% of theory) of 4,4,4-tribromobutyric acid chloride; boiling point 71 to 730 C /0.05 mm Hg.

b) Preparation of2-chloro-4,4,4-tribromobutyric acid chloride 343.2 g (1.0 mol) of 4,4,4-tribromobutyric acid chloride are dissolved in 600 g of thionyl chloride, and 266.0 g (2.0 mols) of N-chlorosuccinimide are added portionwise at 60"C, with the mixture being simultaneously irradiated with a mercury high-pressure discharge lamp. After the addition of N-chlorosuccinimide is completed, the resulting mixture is stirred for 5 hours at 60"C whilst being irradiated. The thionyl chloride is then distilled off, and the residue is rectified under high vacuum to yield 309.7 g (82% of theory) of 2-chloro-4,4,4-tribromobutyric acid chloride; boiling point 59 to 63"C /0.05 mm Hg.

c) Preparation of 2-r2',2',2'-tribromoethyll-2-chloro-3,3-dimethylcyclobutan- 1-one 90.6 g (0.24 mol) of 2-chloro-4,4,4-tribromobutyric acid chloride in 360 ml of cyclohexane are placed into an autoclave, and 134 g (2.4 mols) of isobutylene are injected. A solution of 24.2 g (0.24 mol) of triethylamine in 120 ml of cyclohexane is subsequently pumped in at 65"C in the course of 4 hours. After the triethylamine solution has been added, the reaction mixture is held for a further 3 hours at 65"C. The triethylamine hydrochloride which has formed is then filtered off, and the solvent is distilled off. The residue is dissolved in a solvent mixture consisting of equal parts of toluene and hexane, and filtered through silica gel.The solvent is evaporated off, and from the filtrate are obtained 51.4 g (54% of theory) of 2-(2',2',2'-tribromoethyl)-2 chloro-3,3-dimethylcyclobutan-1-one; melting point 95 to 97"C.

IR spectrum (CCI4) in cm-1: 1800 (CO).

aH-NMR spectrum (100 MHz, CDCl3) in ppm: 1.39 and 1.41 (each Is; each 3H); 2.86-3.22 (m; 2H) 3.554.15 (m,2H).

d) Preparation of 2-r2',2',2'-tribromoethyl)-3,3-dimethyl-4chlorocyclobutan- 1-one 22.8 g (0.054 mol) of 2-(2',2',2'-tribromoethyl)-2-chloro-3,3-dimethylcyclobutan-1 -one are dissolved in 220 ml of absolute ethanol which has previously been saturated with hydrogen chloride. The solution obtained is stirred for 5 hours at 80"C. The reaction mixture is then concentrated in a rotary evaporator to about 1/3 of the initial volume; water is added and the mixture is extracted with ether. The ether extract is washed firstly with a saturated sodium chloride solution and then with sodium bicarbonate solution, and dried over sodium sulphate. The residue, obtained after the ether has been evaporated off, is chromatographed on silica gel, with toluene being used as the eluant.The yield after combining and concentrating the pure fractions by evaporation is 17.1 g (75% of theory) of 2-(2',2',2'-tribromoethyl)-3,3-dimethyl-4-chlorocyclobutan-1-one; melting point 87 to 89"C.

IR spectrum (CCI4) in cm-1: 1805 (CO).

1H-NMR spectrum (100 MHz, (CDC13) in ppm: 1.14 and 1.67 (each Is; each 3H); 3.08 to 3.68 (m; 3H); 4.77 (d; lH).

e) Preparation of 2-g2',2'-dibromovinyl)-3,3-dimethyl-cyclopropane- 1-carboxylic acid 5.6 ml of 5% sodium hydroxide solution are added to 800 mg (2 mmol) of 2-(2',2',2'-tribromoethyl)-3,3 dimethyl-4-chlorocyclobutan-1 -one at O"C. The mixture obtained is stirred firstly for 18 hours at 0 C and subsequently for 1 hour at 80"C. The reaction mixture is then washed with diethyl ether, and afterwards acidifed, with cooling, with concentrated hydrochloric acid, and extracted with diethyl either. The extract is washed with water, dried over magnesium sulphate and concentrated by evaporation. The yield is 0.59 g (100% of theory) of 2-(2',2'-dibromovinyl)-3,3-dimethylcyclopropane-1 -carboxylic acid, which consists of 80% by weight of the cis-isomer and 20% by weight of the trans-isomer.

IR spectrum (CHC13) in cm-': 1695 (CO).

1H-NMR spectrum (100 MHz, CDCI3) in ppm: 1.25 and 1.35, as well as 1.30 and 1.31 (each Is; each 2 CH3 groups of the trans- and cis-compound); 1.62 to 2.30 (m; 2H), 6.15 and 6.70 (each I d; intensity ratio 1 :4, total integral 1H).

Claims (25)

1. A process for the preparation of a 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1-one of the formula I

in which one of the radicals R1 and R2 is methyl and the other is hydrogen or methyl, or R1 and R2 together are an alkylene group having 2 to 4 carbon atoms, which comprises reacting 2-chloro-4,4,4-tribromobutyric acid chloride of the formula II

in the presence of an organic base with an olefine of the formula III

in which R1 and R2 are as defined under formula I, to give a 2-(2',2',2'4ribromoethyl)-2-chlorocyclobutan-1 one of the formula IV

in which R1 and R2 are as defined under formula I, and then rearranging the latter, in the presence of a catalyst, into a 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1 -one of the formula I.

2. A process according to claim 1, which comprises using an olefine of the formula Ill in which one of the radicals R1 and R2 is methyl and the other is hydrogen or methyl, or R1 and R2 together are an alkylene group having 2 to 3 carbon atoms.

3. A process according to claim 1, which comprises using isobutylene as the olefine of the formula Ill.

4. A process according to claim 1, which comprises using methylenecyclopropane as the olefine of the formula III.

5. A process according to claim 1, which comprises carrying out the reaction of the 2-chloro-4,4,4tribromobutyric acid chloride of the formula II with an olefine of the formula Ill in the presence of pyridine or of a trialkylamine having 1 to 4 carbon atoms in each alkyl group and in the presence of an inert organic solvent.

6. A process according to claim 1, which comprises carrying out the reaction of the 2-chloro-4,4,4tribromobutyric acid chloride of the formula II with an olefine of the formula Ill in the presence of triethylamine.

7. A process according to claim 1, which comprises using an inorganic or organic proton acid as the catalyst for the rearrangement of a 2-(2',2',2'-tribromoethyl)-2-chlorocyclobutan-1 -one of the formula IV into a 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1 -one of the formula I.

8. A process according to claim 1, which comprises using a hydrogen halide acid as the catalyst for the rearrangement of a 2-(2',2',2'-tribromoethyl)-2-chiorocyclobutan-1 -one of the formula IV into a tribromoethyl)-4-chlorocyclobutan-1 -one of the formula I.

9. A process according to claim 1, which comprises using an organic base as the catalyst for the rearrangement of a 2-(2',2',2'-tribromoethyl)-2-chlorocyclobutan-1-one of the formula IV into a 2-(2',2',2'tribromoethyl)-4-chlorocyclobutan-1 -one of the formula I.

10. A process according to claim 1,which comprises using an amine of the formula

in which Q1 is alkyl having 1 to 8 carbon atoms, cycloalkyl having 5 to 6 carbon atoms, benzyl or phenyl and Q2 and 03 independently of one another are hydrogen or alkyl having 1 to 8 carbon atoms, as the catalyst for the rearrangement of a 2-(2',2',2'-tribromoethyl)-2-chlorocyclobutan-1 -one of the formula IV into a 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1-one of the formula I.

11. A process according to claim 1, which comprises using a salt of a proton acid with ammonia, a nitrogen-containing organic base or a quaternary ammonium salt as the catalyst for the rearrangement of a 2-(2',2',2'-tribromoethyl)-2-chlorocyclobutan-1-one of the formula IV into a 2-(2',2',2'-tribromoethyl)+ chlorocyclobutan-1-one of the formula I.

12. A process according to claim 1, which comprises using a salt of a hydrogen halide acid with an aliphatic, cycloaliphatic, araliphatic or aromatic primary, secondary or tertiary amine or a heterocyclic nitrogen base as the catalyst for the rearrangement of a 2-(2',2',2'-tribromoethyl)-2-chlorocyclobutan-l-one of the formula IV into a 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1-one of the formula I.

13. A process according to claim 1,which comprises using a salt of the formula

in which M is fluorine, bromine or iodine and especially chlorine, Q4 iS hydrogen, alkyl having 1 to 18 carbon atoms, cyclohexyl, benzyl, phenyl or naphthyl and 05, Q6 and Q7 independently of one another are hydrogen or alkyl having 1 to 18 carbon atoms, or a N-alkylpyridinium halide having 1 to 18 carbon atoms in the alkyl group, as the catalyst for the rearrangement of a 2-(Z',2',2'-tribromoethyl)-2-bromoethyl)-2- chlorocyclobutan-1-one of the formula IV into a 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1-one of the formula

14.A process according to claim 1, which comprises carrying out the rearrangement of a 2-(2',2',2' tribromoethyl)-2-chlorocyclobutan-1-one of the formula IV into a 2-(2',2',2'-tribromoethyl)4- chlorocyclobutan-1-one of the formula I at temperatures of between 80 and 130" C.

15. A process according to claim 1, which comprises carrying out the rearrangement of a 2-(2',2',2' tribromoethyl)-2-chlorocyclobutan-1-one of the formula IV into a 2-(2',2',2'-tribromoethyl)-4chlorocyclobutan-1-one of the formula I in the melt at a temperature of between 80 and 130 C in the presence of a trialkylamine having 1 to 8 carbon atoms in each alkyl group or of a tetraalkylammonium halide having 1 to 18 carbon atoms in the alkyl groups.

16. A process according to claim 1, which comprises carrying out rearrangement of a 2-(2',2',2'tribromoethyl)-2-chlorocyclobutan-1 -one of the formula IV into a 2-(2',2',2'-tribromoethyl)-4- chlorocyclobutan-1-one of the formula I in the presence of an inert solvent.

17. A process according to claim 1, which comprises carrying out the rearrangement of a 2-(2',2',2'tribromoethyl)-2-chlorocyclobutan-1 -one of the formula IV into a 2-(2',2',2'-tribromoethyl)-4 chlorocyclobutan-1-one of the formula I in an aliphatic alcohol having 1 to 4 carbon atoms, toluene, xylene, chlorobenzene, dioxane, acetonitrile, 3-methoxypropionitrile, ethylene glycol, diethyl ether or diisopropyl ketone, as the solvent.

18. A 2-chloro-4,4,4-tribromobutyric acid chloride of the formula II

19. A 2-(2',2',2'-tribromoethyl)-2-chlorocyclobutan-1-one of the formula IV

in which one of the radicals R1 and R2 is methyl and the other is hydrogen or methyl, or R1 and R2 together are alkylene having 2 to 4 carbon atoms.

20. A 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1 -one of the formula I

in which one of the radicals R1 and R2 is methyl and the other is hydrogen or methyl, or R1 and R2 together are alkylene having 2 to 4 carbon atoms.

21. The use of a 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1-one of the formula I

in which one of the radicals R1 and R2 is methyl and the other is hydrogen or methyl, or R1 and R2 together are alkylene having 2 to 4 carbon atoms, for the preparation of a compound of the formula VIII

in which one of the radicals R1 and R2 is methyl and the other is hydrogen or methyl, or R1 and R2 together are alkylene having 2 to 4 carbon atoms, X is chlorine or bromine and R is hydrogen, alkyl having 1 to 4 carbon atoms or a group of the formula IX

in which R3 is oxygen, sulphur or a vinylene group, R4 is hydrogen, alkyl having 1 to 4 carbon atoms, benzyl, phenoxy or phenylmercapto, Rg is hydrogen or an alkyl group having 1 to 4 carbon atoms and R6 is hydrogen, cyano or ethynyl, or, if one of the radicals R1 and R2 is methyl and the other is hydrogen or methyl, R3 is a vinylene group, R4 is phenoxy and Rg is hydrogen, also alkyl having 1 to 5 carbon atoms.

22. A process according to Claim 1 substantially as described in the foregoing Example.

23. A 2-(2',2',2'-tribromoethyl)-4-chlorocyclobutan-1-one of the formula I as defined in Claim 1 when prepared by the process claimed in any of Claims 1 to 17 or 22.

24. A process for the preparation of a compound of the formula VIII as defined in Claim 21 which comprises heating with a base a compound of the formula las defined in Claim land reacting the product with an appropriate alcohol.

25. A compound of the formula VIII as defined in Claim 21 when produced by the process of Claim 24.