GB2140803A - Herbicidal tetrahydropyran-2,4-dione derivatives - Google Patents

Abstract

The invention concerns novel compounds of the formula I <IMAGE> wherein: n is an integer selected from 1 to 5; X is selected from halogen, nitro, cyano, alkyl, substituted alkyl, hydroxy, alkoxy, substituted alkoxy, alkenyl, alkenyloxy, alkynyl, alkynyloxy, acyloxy, alkoxycarbonyl, alkylthio, alkylsulfinyl, alkylsulfonyl, sulfamoyl, substituted sulfamoyl, alkanoyloxy, benzyloxy, substituted benzyloxy, amino, substituted amino and the groups formyl and alkanoyl and the oxime, imine and Schiff base derivatives thereof; R<1> is selected from hydrogen, alkyl, alkenyl, alkynyl, substituted alkyl, alkylsulfonyl, arylsulfonyl, acyl and an inorganic or organic cation; R<2> is selected from alkyl, substituted alkyl, alkenyl, haloalkenyl, alkynyl and haloalkynyl; and R<3> is selected from alkyl, fluoroalkyl, alkenyl, alkynyl, and phenyl. The compounds of the invention show herbicidal properties and plant growth regulating properties and in further embodiments the invention provides processes for the preparation of compounds of formula I, intermediates useful in the preparation of the compounds of formula I, compositions containing as active ingredient a compound of formula I, and herbicidal and plant growth regulating processes utilizing compounds of formula I.

Description

SPECIFICATION Herbicidal tetrahydropyran-2,4-dione derivatives This invention relates to organic compounds having biological activity and in particular to organic compounds having herbicidal properties and plant growth regulating properties, to processes for the preparation of such compounds, to intermediates useful in the preparation of such compounds and to herbicidal compositions and processes utilizing such compounds and to plant growth regulating compositions and processes utilizing such compounds.

It is known in the art that certain 3,4-dihydro-2H-pyran-2,4-dione derivatives show herbicidal activity against monocotyledonous plants or grasses. For example United States Patent No.

4,008,067 discloses a group of 3-(1-alkoxyaminoalkylidene) tetra-hydropyran-2,4-dione derivatives which are substituted in the 5 and/or 6-positions of the pyran ring by one or two alkyl groups, and which are active as grass herbicides.

It has now been found that certain tetrahydropyran-2,4-dione derivatives which are substituted in the 6-position of the pyran ring with a substituted phenyl group exhibit particularly useful herbicial activity.

Accordingly the invention provides a compound of formula I

wherein: n is an integer selected from 1 to 5; X, which may be the same or different, are independently selected from the group consisting of: halogen; nitro; cyano; C1 to C6 alkyl; C, to Ce alkyl substituted with a substituent selected from the group consisting of halogen, nitro, hydroxy, C1 to Ce alkoxy and C1 to C6 alkylthio; C2 to Ce alkenyl; C2 to Ce alkylnyl; hydroxy; C1 to Ce alkoxy; C1 to Ce alkoxy substituted with a substituent selected from halogen and C1 to C6 alkoxy; C2 to C6 alkenyloxy; C2 to C6 alkynyloxy; C2 to C6 alkanoyloxy; (C1 to C6 alkoxy)carbonyl; C1 to C6 alkylthio; C, to C6 alkylsulfinyl;C1 to C6 alkylsulfonyl; sulfamoyl; N-(C1 to Ce alkyl)sulfamoyl; N,N-di(C1 to Ce alkyl)sulfamoyl; benzyloxy; substituted benzyloxy wherein the benzene ring is substituted with from one to three substituents selected from the group consisting of halogen, nitro, C, to Ce alkyl, C, to Ce alkoxy and C1 to Ce haloalkyl; the group NR5R6 wherein R5 and R6 are indepedendently selected from the group consisting of hydrogen, C1 to C6 alkyl, C2 to C6 alkanoyl, benzoyl and benzyl; the groups formyl and C2 to C6 alkanoyl and the oxime, imine and Schiff base derivatives thereof; R' is selected from the group consisting of: hydrogen; C1 to C6 alkyl; C2 to C6 alkenyl;C2 to C6 alkynyl; substituted C1 to C6 alkyl wherein the alkyl group is substituted with a substituent selected from the group consisting of C1 to C6 alkoxy, C1 to C6 alkylthio, phenyl and substituted phenyl wherein the benzene ring is substituted with from one to three substituents selected from the group consisting of halogen, nitro, cyano, C, to C6 alkyl, C, to C6 haloalkyl, C1 to C6 alkoxy and C1 to C6 alkylthio; C1 to C6 (alkyl) sulfonyl; benzenesulfonyl; substituted benzenesulfonyl wherein the benzene ring is substituted with from one of to three substituents selected from the group consisting of halogen, nitro, cyano, C1 to C6 alkyl, C1 to C6 haloalkyl; C1 to C6 alkoxy and C1 to C6 alkylthio; and acyl group; and an inorganic or organic cation; R2 is selected from the group consisting of:C1 to C6 alkyl; C2 to C6 alkenyl; C2 to C6 haloalkenyl; C2 to C6 alkynyl; C2 to C6 haloalkynyl; substituted C1 to C6 alkyl wherein the alkyl group is substituted with a substituent selected from the group consisting of halogen, C1 to C6 alkoxy, C1 to C6 alkylthio, phenyl and substituted phenyl wherein the benzene ring is substituted with from one to three substituents selected from the group consisting of halogen, nitro, cyano, C, to C6 alkyl, C1 to C6 haloalkyl, C1 to C6 alkoxy and C1 to C6 alkylthio; and R3 is selected from the group consisting: C1 to C6 alkyl; C1 to C6 fluoroalkyl; C2 to C6 alkenyl; C2 to C6 alkynyl; and phenyl.

When in the compound of formula I X is chosen from the groups formyl and C2 to C6 alkanoyl and the oxime, imine and Schiff base derivatives thereof, the nature of the oxime, imine and Schiff base derivatives is not narrowly critical. Although not intending to be bound by theory, it is believed that in the plant the (substituted) imine group may be removed to give the corresponding compound of formula I in which X is formyl or C2 to C6 alkanoyl. Suitable values for the groups formyl and C2 to C6 alkanoyl and the oxime, imine and Schiff base derivatives thereof include groups of the formula -C(R7) = NR8 wherein R7 is chosen from hydrogen and C to C5 alkyl, and R8 is chosen from hydrogen, C1 to C6 alkyl, phenyl, benzyl, hydroxy, C1 to C6 alkoxy, phenoxy and benzyloxy.

When in the compound of formula I R1 is chosen from acyl the nature of the acyl group is not narrowly critical. Although not intending to be bound by theory, it is believed that when R' is acyl the acyl group may be removed in the plant by hydrolysis to give the corresponding compound of formula I in which R1 is hydrogen. Suitable acyl groups include: alkanoyl, for example C2 to C6 alkanoyl; aroyl, for example benzoyl and substituted benzoyl wherein the benzene ring is substituted with from one two three substituents chosen from the group consisting of halogen, nitro, cyano, Ct to C6 alkyl, Ct to C6 haloalkyl, Ct to C6 alkoxy and C1 to C6 alkylthio; and heteroaroyl, for example 2-furoyl, 3-furoyl, 2-thenoyl and 3-thenoyl.

When in the compound of formula I R1 is chosen from an inorganic or organic cation the nature of the cation is not narrowly critical. Although not intending to be bound by theory, it is believed that when R1 is a cation the cation may be removed in the plant to give a compound of formula I wherein R1 is hydrogen. Suitable inorganic catins include the alkali and alkaline earth metal ions, heavy metal ions including the transition metal ions, and the ammonium ion.

Suitable organic cations include the cation- R9R'0R1tRt2Nf3 wherein R9, R10, R11 and R12 are independently chosen from the group consisting of: hydrogen; C1 to C10 alkyl; substituted C1 to C10 alkyl wherein the alkyl groups is substituted with a substituent chosen from the group consisting of hydroxy, halogen and C1 to C6 alkoxy; phenyl; benzyl; and the groups substituted phenyl and substituted benzyl wherein the benzene ring is substituted with from one to three substituents chosen from the group consisting of halogen, nitro, cyano, C1 to C6 alkyl, C1 to C6 haloalkyl, C1 to C6 alkoxy and C1 to C6 alkylthio.

It should be recognized that when R1 is hydrogen the compounds of the invention may exist in any one of four tautomeric forms as shown below wherein (b represents the group

Preferred compounds of the invention include those compounds of formula I wherein: X are independently selected from the group consisting of C1 to C6 alkyl, C1 to C6 alkoxy, C1 to C6 alkylthio, halogen and C2 to C6 alkanoyl; R1 is selected from the group consisting of hydrogen, alkali metal, ammonium, C1 to C10 alkylammonium, C2 to C6 alkanoyl, benzoyl and substituted benzoyl wherein the benzene ring is substituted with from one to three substituents selected from the group consisting of halogen, nitro and cyano; R2 is selected from the group consisting of methyl, ethyl, n-propyl, allyl and propargyl; ; R3 is selected from the group consisting of methyl, ethyl and n-propyl; and n is an integer selected from 1 to 5.

More preferred compounds of the invention include those compounds of formula I wherein: X are independently selected from the group consisting of C1 to C6 alkyl, C1 to C6 alkoxy, C1 to C6 alkylthio and C2 to C6 alkanoyl; R1 is selected from hydrogen and C2 to C6 alkanoyl; R2 is selected from ethyl and allyl; R3 is selected from ethyl and n-propyl; and n is an integer selected from 1 to 5.

Even more preferred compounds of the invention include those compounds of formula

wherein: X2, X4 and X6 are methyl; X is selected from methyl and acetyl; R1 is hydrogen; R2 is selected from ethyl and allyl; R3 is ethyl; and n is selected from zero and the integers 1 and 2.

Specific examples of the compounds of the invention include those compounds detailed in Table 1 below Table 1

Compound No. (X)n R1 R2 R3 1 4-CH3 H C2H6 C2H5 2 2,4,6-(CH3)3 H C2H5 C2H6 3 4-CH3O H C2H5 C2H5 4 4-CH3S H C2H5 C2H5 5 . 3-CH3CO-2,4,6-(CH3)3 H C2H5 C2H5 6 2,4,6-(CH3)3 H CH2CH = CH2 C2H5 7 2,4,6-(CH3)3 a CH2CH = CH2 C2H5 Code: a COCH2CH(CH3)2 The compounds of the invention may be prepared by a variety of methods and in a further aspect the invention provides methods for the preparation of compounds of formula I.

Conveniently the preparation of the compounds of the invention can be considered in three or four parts.

Part A involves the formation of a 6-aryl tetrahydro-pyran-2,4-dione of formula IX. This reaction may be carried out in a two step process by: (i) reacting, in the presence of titanium tetrachloride and an alcohol of formula ROH (wherein R is C, to C6 alkyl), an aldehyde of formula V with diketene (lV) to form a 8-hydroxy-ss-ketoester of formula VI; and treating the 8-hydroxy-ss-ketoester of formula VI with a base to give a 6 aryltetrahydro-pyran-2,4-dione of formula IX; or (ii) reacting an aldehyde of formula V with the dianion of a ssketoester of formula VI (wherein R is C, to C6 alkyl), to form a ô-hydroxy-ss-ketoester of formula VI; and treating the 8-hydroxy-ss- ketoester of formula VI with a base to give a 6-aryltetrahydropyran-2,4-dione of formula IX; or (iii) reducing a pyrone of formula VIII to give a 6-aryltetrahydropyran-2,4-dione of formula IX.

Part B involves the acylation of a compound of formula IX to give a 3-acyl-6-aryltetrahydropyran2,4-dione of formula XI. This reaction may be carried out by reacting a 6-aryltetrahydropyran2,4-dione of formula IX with: (iv) a carboxylic acid of formula X in the presence of diethylcyanophosphonate and a base such as triethylamine.

Part C involves the formation of a compound of the invention of formula I wherein R' is hydrogen, that is a compound of formula II. This reaction may be carried out either by reacting a 3-acyl-6-aryltetrahydro-pyran-2 , 4-dione of formula VI with: (v) an alkoxyamine derivative of formula XII; or (vi) hydroxylamine to give an intermediate oxime derivative of formula XIII and reacting that intermediate oxime derivative of formula XIII with an alkylating agent of formula XIV wherein L is a leaving group such as, for example, chloride, bromide, iodide, sulfate, nitrate, methyl sulfate, ethyl sulfate, tetrafluoroborate, hexafluorophosphate, hexafluoroantimonate, methanesulfonate and trifluoromethanesulfonate.

Part D involves the formation of a compound of the invention of formula I wherein R' is a substituent other than hydrogen.

Compounds of the invention of formula I, wherein R' forms an ether, acryl or sulfonyl derivative of a compound of formula II, may be prepared from the corresponding compounds of the invention of formula II by reacting with an etherification, acylation or sulfonylation reagent of formula XV.

Compounds of the invention of formula I wherein R1 is an inorganic or organic cation may be prepared from the compounds of the invention of formula I wherein R' is hydrogen, that is, compounds of formula li, by reacting said compounds of formula II with an inorganic or organic salt. For example, the compounds of formula I wherein R' is an alkali metal ion may be prepared by reacting the appropriate compound of formula II with the appropriate alkali metal hydroxide or alkoxylate. The compounds of formula I wherein R' is a transition metal ion or an organic cation may similarly be prepared by reacting the appropriate compound of formula II with an appropriate transition metal salt or organic base.Alternatively, the compounds of formula I wherein R' is a transition metal ion or an organic cation may be prepared by reacting the appropriate compound of formula I wherein R' is an alkali metal ion with an appropriate transition metal salt or organic salt.

Accordingly, in a further aspect the invention provides a process for the preparation of a compound of formula I, as hereinbefore defined, which process comprises: reacting 3-acyl-6-(aryl) tetrahydropyran-2,4-dione derivative of formula Xl with an alkoxyamine derivative of formula XII to give a compound of the invention of formula II or reacting the 3acyl-6-(aryl) tetrahydropyran-2,4-dione derivative of formula Xl with hydroxylamine and alkylating the oxime intermediate of formula XIII with an alkylating agent of formula XIV, wherein L is a leaving group, to give a compound of the invention of formula II; and optionally reacting the compound of the invention of formula II with a compound of formula XV, wherein L is a leaving group, to give a compound of the invention of formula I.

Certain of the intermediate compounds of formulae VI, IX, Xl and XIII are novel compounds and therefore in further embodiments the invention provides novel compounds of formulae VI, IX, Xl and XIII and processes for the preparation thereof.

The structures of the compounds described above are detailed on the following pages wherein ld represents the group

#-CHO V

CH3 - CO - CH2 CO2 R VII

The compounds of formula I are active as herbicides and therefore, in a further aspect the invention provides a process for severely damaging or killing unwanted plants which process comprises applying to the plants, or to the growth medium of the plants, an effective amount of a compound of formula I as herein before defined.

Generally speaking the compounds of formula I are herbicidally effective against a variety of plants. However, certain of the compounds of the invention are selectively active against monocotyledonous plants, dicotyledonous plants being relatively unaffected by rates of application of the compounds of the invention which are severely damaging or lethal to other plant species.

Moreover, certain of the compounds of formula I are selectively active within the group of monocotyledonous plants and may be used at a rate sufficient to control monocotyledonous weeds in cultivated crops, especially wild grasses in cereal crops. Certain of such compounds of the invention are especially useful in the control of wild grasses such as wild oats and rye grass in crops of cultivated monocotyledonous plants such as wheat, barely and other varieties of cereals.

Accordingly, in yet a further aspect the invention provides a process for controlling monocotyledonous weeds in cultivated crops, especially wild grasses in cereal crops such as wheat, which process comprises applying to the crop, or to the growth medium of the crop, a compound of formula I, as hereinbefore defined, in an amount sufficient to severely damage or kill the weeds but insufficient to damage the crop substantially.

The compounds of formula I may be applied directly to the plant (post-emergence application) or to the soil before the emergence of the plant (pre-emergence application). However, the compounds are, in general, more effective when applied to the plant post-emergence.

The compounds of formula I may be used on their own to inhibit the growth of, severely damage, or kill plants but are preferably used in the form of a composition comprising a compound of the invention in admixture with a carrier comprising a solid or liquid diluent.

Therefore, in yet a further aspect the invention provides growth inhibiting, plant damaging, or plant killing compositions comprising a compound of formula I as hereinbefore defined and an inert carrier therefor.

Certain of the compounds of formula I exhibit useful plant growth regulating activity. For example, while compounds of formula I are selectively active herbicides against wild grasses in crops of cultivated plants at some rates of application they exhibit plant growth regulating effects in said crops.

Plant growth regulating effects may be manifested in a number of ways. For example, suppression of apical dominance, stimulation of auxiliary bud growth stimulation of early flowering and seed formation, enhancement of flowering and increase in seed yield, stem thickening, stem shortening and tillering. Plant growth regulating effects shown in compounds of the invention may include, for example, tillering and stem shortening in crops such as wheat and barley.

Accordingly in a still further aspect the invention provides a process for regulating the growth of a plant which process comprises applying to the plant, to the seed of the plant, or to the growth medium of the plant, an effective amount of a compound of formula I, as herein before defined.

To effect the plant growth regulating process of the present invention the compounds of formula I may be applied directly to the plant (post-emergence application) or to the seed or soil before the emergence of the plani (pre-emergence) application.

The compounds of formula I may be used on their own to regulate the growth of plants but in general are preferably used in the form of a composition comprising a compound of the invention in admixture with a carrier comprising a solid or liquid diluent. Therefore, in a still further aspect the invention provides plant growth regulating compositions comprising a compound of formula I as hereinbefore defined and an inert carrier therefor.

Compositions according to the invention include both dilute compositions, which are ready for immediate use, and concentrated compositions, which require to be diluted before use, usually with water. Preferably the compositions contain from 1 ppm to 99% by weight of the active ingredient. Dilute compositions ready for use preferably contain from 1 ppm to 2% of active ingredient, while concentrated compositions may contain from 5 to 99% of active ingredient, although from 10 to 60% is usually preferred.

The solid compositions may be in the form of granules, or dusting powders wherein the active ingredient is mixed with a finely divided solid diluent, eg kaolin, bentonite, kieselguhr, dolomite, calcium carbonate, talc, powdered magnesia, Fuller's earth and gypsum. They may also be in the form of dispersible powders or grains, comprising a wetting agent to facilitate the dispersion of the powder or grains in liquid. Solid compositions in the form of a powder may be applied as foliar dusts.

Liquid compositions may comprise a solution or dispersion of an active ingredient in water optionally containing a surface-active agent, or may comprise a solution or dispersion of an active ingredient in a water-immiscible organic solvent which is dispersed as droplets in water.

The rate of application of the compounds of the invention will depend on a number of factors including, for example, the compound chosen for use, the identity of the plants to be treated, the formulations selected for use and whether the compound is to be applied for foliage or root uptake. As a general guide, however, an application rate of from 0.001 to 10 kilograms per hectare is suitable while from 0.01 to 5 kilograms per hectare may be preferred.

The compositions of the invention may comprise, in addition to one or more compounds of the invention, one or more compounds not of the invention but which possess biological activity. For example, as herein before indicated the compounds of the invention are effective herbicides against monocotyledonous weeds, wild grasses, but have little or no herbicidal effect against dicotyledonous plants, broad-leaved plants. As a result, in certain applications where it is desired to protect a cereal crop against both wild grasses and broad-leaved weeds it may be preferred to use a herbicidal composition comprising a mixture of at least one herbicidal compound of formula I as hereinbefore defined and at least one other herbicide active against broad-leaved weeds.

Example 1 3-[1 -(Ethoxysmino)propyl]-6-(4-methylphenyl)tetrahydropyran-2, 4-dione ( 1 ) (i) A solution of 4-methylbenzaldehyde (6.0 g; 50 mmole) and diketene (8.4 g; 100 mmole) in dichloromethane (200 ml) was stirred and cooled to - 70"C in a dry ice bath. A solution of titanium tetrachloride (11 g; 58 mmole) in dichloromethane (20 ml) was added dropwise so that the temperature of the reaction mixture did not exceed - 50"C. The resultant dark solution was stirred for a further 30 minutes at - 70"C and then methanol (80 ml) was added slowly and the mixture was allowed to warm to room temperature. The solution was poured into cold dilute hydrochloric acid (0.5 mole, 200 ml) and the organic layer was separated.The aqueous layer was extracted with more dichloromethane and the combined extracts were concentrated under reduced pressure to give a pale brown oil. The oil was stirred vigourously with a solution of sodium hydroxide (4 g) in water (600 ml) at room temperature for 2 hours. The mixture was extracted with toluene (75 ml) and the aqueous layer was separated and acidified to pH 4 with dilute hydrochloric acid. The resultant precipitate was removed by filtration, washed with nhexane and dried to give 6-(4-methylphenyl)tetrahydropyran-2,4-dione as a colourless solid (3.1 g, 30%), mp 130 C.

(ii) To a solution of 6-(4-methylphenyl)tetrahydropyran-2,4-dione (1.5 g; 7.5 mmole) and triethylamine (1.5 g; 15 mmole) in dimethylformamide (10 ml) at 5"C was added a cooled solution of propionic acid (0.6 g; 8 mmole), triethylamine (0.8 g; 8 mmole) and diethyl cyanophosphate (1.25 g; 8 mmole) in dimethylformamide (10 ml). The mixture was stirred at room temperature for 2 hours, poured into cold water (200 ml) and extracted with diethyl ether (2 X 50 ml). The ether extracts were dried over magnesium sulphate, filtered and evaporated and the crude product was purified by chromatography over silica gel (eluant dichloromethane) to give 6-(4-methylphenyl)-3-propionyltetrahydropyran-2,4-dione (1.0 g 52%) as a pale yellow solid, mp 102 C.

(iii) Ethoxyamine hydrochloride (400 mg; 4 mmole) and then anhydrous sodium acetate (350 mg; 4 mmole) were added with stirring to a solution of 6-(4-methylphenyl)-3-propionyltetrahy- dropyran-2,4-dione (1.0 g; 4 mmole) in ethanol (100 ml) at room temperature. The mixture was stirred, for 4 hours and then the ethanol removed under reduced pressure and the residue was partitioned between dichloromethane and water. The organic phase was dried over anhydrous magnesium sulphate and the solvent was removed under reduced pressure to give 3-[1 (ethoxyimino)prnpyl]-6-(4-methylphenyl)tetrnhydropyran-2,4-dione (850 mg; 80%) as a pale yellow low-melting point solid.

The product was characterized by proton nuclear magnetic resonance spectroscopy and the.

data is recorded in Table 2, Example 3.

Example 2 Compounds No 2, 3, 4 and 6 (see Table 1) were prepared from the appropriate substituted benzaldehyde following essentially the same procedure as that described in Example 1 parts (i) to (iii). Each of the products was characterized by proton nuclear magnetic resonance spectroscopy and the spectroscopic data is recorded in Table 2, Example 5.

Example 3 3-fl -(Ethoxyimino)prnpylj-6-(3-acetyl-2, 4, 6-trimethylphenylJtetrahydropyran-2,4-dione (5) (i) A solution of 6-(2,4,6-trimethylphenyl)-3-propionyltetrahydropyran-2,4-dione (2.0 g) in dichloroethane (1 0 ml) was added with stirring to an ice cold solution of aluminium trichloride (3.88 g) in dichloroethane (15 ml). To this mixture was then added acetyl chloride (0.59 g) in dichloroethane (6 ml) and the reaction mixture was stirred for a further 30 minutes at 0 C and then for 1.5 hours at 20 C. The solution was poured into ice cold 5 M hydrochloric acid (100 ml) and stirred for 0.5 hours. The organic layer was separated and the aqueous layer extracted with dichloromethane (100 ml).The combined organic extracts were washed with water, dried over magnesium sulphate, filtered and evaporated to give a dark oil which was purified by column chromatography (silica gel, eluant åichloromethane) to give 6-(3-acetyl-2,4,6-trimethyl- phenyl)-3-propionyltetrahydropyran-2,4-dione (50 rung, 2.5%) as an orange oil. Proton nuclear magnetic resonance spectrum (CDCl3; Sin ppm): 1.20 (3H,t); 2.14 (3H,s); 2.29 (3H, s); 2.37 (3H,s); 2.45 (3H,s); 2.5-3.5 (4H,m); 5.80 (1hid oft); 6.89 (1H,s); 17.95 (iH,s).

(ii) Reaction of 6-(3-acetyl-2,4, 6-trimethylphenyl)-3-propionyltetrahydropyran-2,4-dione with ethoxyamine hydrochloride was carried out following essentially the same procedure as described in Example 1, part (iii) to give 3-(1 -(ethoxyimino)propyl]-6-(3-acetyl-2,4,6-trimethyl- phenyl)tetrahydropyran-2,4-dione (5) as a yellow oil.

The product was characterized by proton nuclear magnetic resonance spectroscopy and the data is recorded in Table 2, Example 5.

Example 4 44sovaleryloxy-3-f 1 -(a II ylox yim in o) prnpylj- 6-(2, 4, 6-trimefflylphenyl)-5, 6-dihydro-2H-pyranone (7) To a solution of 3-Fl -(allyloxyimino)prnpyl-6-(2, 4, 6-trimethylphenyl)tetrahydropyran-2,4-dione (6) (0.46 g) in dichloromethane (50 ml) was added to 4-picoline (0.14 g), followed by isovalerylchloride (0.1 8 g) with stirring at room temperature. After 1 hour the solution was washed with dilute hydrochloric acid, followed by water and then separated and dried.

Evaporation of the solvent gave 4-isovaleryloxy-3-[1-(allyloxyimino)propyl]-6-(2,4,6-trimethylphe- nyl)-5,6-dihydro-2H-pyranone as a yellow oil (400 mg, 77%).

The product was characterized by proton nuclear resonance spectroscopy and the data is recorded in Table 2, Example 5.

Example 5 The majority of the compounds of the invention were obtained as oils and were characterized by, and may be identified by, their proton nuclear magnetic resonance (pmr) spectra. For convenience, physical data and pmr spectroscopic data are recorded in Table 2 below.

TABLE 2 Compound Proton Chemical Shift No Appearance 8 in ppm (CDCl3) 1 pale yellow 1.21(3H,t); 1.34(3H,t); 2.34(3H, low-melting s); 2.4-4.30(4H,m); 4.12(2H,q); solid 5.3(1H,dofd); 7.23(4H,dofd); 15.0(1 H,bs).

2 pale yellow 1.25(3H,t); 1.35(3H,t); 2.26(3H, oil s); 2.38(6H,s); 2.4-3.1(4H,m); 4.13(2H,q); 5.76(1H,dofd); 7.25 (2H,s); 15.0(1 H,bs).

3 pale yellow 1.16-1.46(6H,m); 2.58-3.21(4H,m); solid 3.8'1(3H,s); 412(2H,q); 5.27-5.43 (1H,dofd); 7.13(4H,dofd); 15.0 (1 H,bs).

4 pale brown 1.10-1.47(6H,m); 2.48(3H,s); 2.65 solid 3.29(4H,m); 4.13(3H,q); 5.31-5.48 (1H,dofd); 7.33(4H,s); 15.0 -(1 H,bs).

5 yellow oil 1.12-1.55(6H,m); 2.18(3H,s); 2.29 (3H,s); 2.38(3H,s); 2.44(3H,s); 2.35-3.30(4H,m); 4.16(2H,q); 5.80 (1H,dofd); 6.88(1H.s); 15.14(1 H, s).

6 pale yellow 1.25(3H,t); 2.25(3H,s); 2.38 solid mp (6H,s); 2.64-3.39(4H,m); 4.55(2H, 99"C d); 5.29-6.26(4H,m); 6.84(2H,s); 14.84(1H, s) 7 yellow oil 0.88-1.20(9H,m); 2.26(3H,s); 2.38 (6H,s); 2.28-2.74(5H,m); 4.60 (2H,d); 5.14-5.37(2H,m); 5.71 6.22(2H,m); 6.85(2H,s).

Example 6 This non-limiting Example illustrates the preparation of formulations of the compounds of the invention.

a) Emulsifiable Concentrate Compound No 2 was dissolved in toluene containing 7% v/v "Teric" N 1 3 and 3% v/v "Kemmat" SC15B to give an emulsifiable concentrate which may be diluted with water to the required concentration to give an aqueous emulsion which may be applied by spraying.

("Teric" is a Trade Mark and "Teric" N 1 3, is a product of ethoxylation of nonylphenol; "Kemmat" is a Trade Mark and "Kemmat" SC15B is a formulation of calcium dodecylbenzenesulfonate.) b) Aqueous Suspension Compound No 2 (5 parts by weight) and "Dyapol" PT (1 part by weight) were added to an aqueous solution (94 parts by weight) of "Terric" N8 and the mixture was ball milled to produce a stable aqueous suspension which may be diluted with water to the required concentration to give an aqueous suspension which may be applied by spraying. ("Dyapol" is a Trade Mark and "Dyapol" PT is an anionic suspending agent; "Teric" N8 is a product of ethoxylation of nonylphenol.) c) Emulsifiable Concentrate Compound No 2 (10 parts by weight), "Teric" N13 (5 parts by weight) and "Kemmat" SC1SB (5 parts by weight) were dissolved in "Solvesso" 1 50 (80 parts by weight) to give an emulsifiable concentrate which may be diluted with water to the required concentration to give an aqueous emulsion which may be applied by spraying. ("Solvesso" is a Trade Mark and "Solvesso" 1 50 is a high boiling point aromatic petroleum fraction.) d) Dispersible Powder Compound No 2 (100 parts by weight), "Matexil" DA/AC (3 parts by weight), "Aerosol" 0T/B (1 part by weight) and china clay 298 (86 parts by weight) were blended and then milled to give a powder composition having a particle size below 50 microns. ("Matexil" is a Trade Mark and "Matexil" DA/AC is the disodium salt of a naphthalenesulfonic acid/formaldehyde condensate; "Aerosol" is a Trade Mark and "Aerosol" OT/B is a formulation of the dioctyl ester of sodium sulfosuccinic acid.) e) High Strength Concentrate Compound No 2 (99 parts by weight), silica aerogel (0.5 parts by weight) and synthetic amorphous silica silica (0.5 parts by weight) were blended and ground in a hammer-mill to produce a powder having a particle size less than 200 microns.

f) Dusting Powder Compound No 2 (10 parts by weight), attapulgite (10 parts by weight) and pyrophyllite (80 parts by weight) were thoroughly blended and then ground in a hammer-mill to produce a powder of particle size less than 200 microns.

Emulsifiable concentrates and/or suspensions of the compounds of the invention were prepared essentially as described in part a), b) or c) above and then diluted with water, optionally containing surface active agent and/or oil, to give aqueous compositions of the required concentration which were used, as described in Examples 7 and 8 in the evaluation of the pre-emergence and post-emergence herbicidal activity of the compounds.

Example 7 The pre-emergent herbicidal activity of the compounds of the invention formulated as described in Example 6 was assessed by the following procedure: The seeds of the test species were sown in rows 2 cm deep in soil contained in seed boxes.

The monocotyledonous plants and the dicotyledonous plants were sown in separate boxes and after sowing the two boxes were sprayed with the required quantity of a composition of the invention. Two duplicate seed boxes were prepared in the same manner but were not sprayed with a composition of the invention and were used for comparison purposes. All the boxes were placed in a glasshouse, lightly watered with an overhead spray to initiate germination and then sub-irrigated as required for optimum plant growth. After three weeks the boxes were removed from the glass house and the effect of the treatment was visually assessed.The results are presented in Table 3 where the damage to plants is rated on a scale of from 0 to 5 where 0 represents from O to 10% damage, 1 represents from 11 to 30% damage, 2 represents from 31 to 60% damage, 3 represents from 61 to 80% damage, 4 represents from 81 to 99% damage and 5 represents 100% kill. A dash (-) means that no experiment was carried out.

The names of the test plants are as follows: Wh Wheat Ot Wild Oats Rg Ryegrass Jm Japanese millet P Peas Ip Ipomea Ms Mustard Sf Sunflower TABLE 3 PRE-EMERGENCE HERBICIDAL ACTIVITY TEST PLANT Compound APPLICATION No Rate (kg/ha) Wh Ot Rg Jm P Ip Ms Sf 5 1.0 5 5 5 5 0 0 0 0 5 0.25 4 5 5 5 0 0 0 0 Example 8 The post-emergent herbicidal activity of the compounds of the invention formulated as described in Example 6 was assessed by the following procedure.

The seeds of the test species were sown in rows 2 cm deep in soil contained in seed boxes.

The monocotyledonous plants and the dicotyledonous plants were sown in separate seed boxes in duplicate. The four seed boxes were placed in a glass house, lightly watered with an overhead spray to initiate germination and then sub-irrigated as required for optimum plant growth. After the plants had grown to a height of about 10 to 1 2.5 cm one box of each of the monocotyledonous plants and the dicotyledonous plants was removed from the glass house and sprayed with the required quantity of a composition of the invention. After spraying the boxes were returned to the glass house for a further 3 weeks and the effect of treatment was visually assessed by comparison with the untreated controls.The results are presented in Table 4 where the damage to plants is rated on a scale of from 0 to 5 where 0 represents from 0 to 10% damage, 1 represents from 11 to 30% damage, 2 represents from 31 to 60% damage, 3 represents from 61 to 80% damage, 4 represents from 81 to 99% damage and 5 represents 100% kill. A dash (-) means that no experiment was carried out.

The names of the test plants are as follows: Wh Wheat Ot Wild Oats Rg Ryegrass Jm Japanese millet P Peas Ip Ipomea Ms Mustard Sf Sunflower TABLE 4 POST-EMERGENCE HERBICIDAL ACTIVITY TEST PLANT Compound APPLICATION No Rate (kg/ha) Wh Ot Rg Jm P Ip Ms Sf 1 1.0 1 5 5 5 0 0 0 0 1 0.25 0 0 4 4 0 0 0 0 2 1.0 0 4 4 5 0 0 0 0 2 0.25 0 4 2 4 0 0 0 0 3 1.0 3 3 5 5 0 0 0 0 3 0.25 0 0 3 5 - - - - 4 1.0 5 5 5 5 0 0 0 0 4 0.25 3 4 5 5 - - - - 4 0.0625 0 2 3 5 - - - - 5 . 1.0 5 5 5 5 0 0 0 0 5 0.25 5 5 5 5 - - - - 5 0.0625 4 5 5 5 - - - - 6 1.0 1 5 5 5 0 0 0 0 6 0.25 0 4 4 3 - - - - 7 1.0 0 5 4 5 0 0 0 0 Example 9 The compounds were formulated for test by mixing an appropriate amount with 5 ml of an emulsion prepared by diluting 160 ml of a solution containing 21.9 g per litre of "Span" 80 and 78.2 g per litre of "Tween" 20 in methylcyclohexanone to 500 ml with water. "Span" 80 is a Trade Mark for a surface-active agent comprising sorbitan monolaurate. "Tween" 20 is a Trade Mark for a surface-active agent comprising a condensate of sorbitan monolaurate with 20 molar proportions of ethylene oxide.Each 5 ml emulsion containing a test compound was then diluted to 40 ml with water and sprayed on to young pot plants (post-emergence test) of the species named in Table 5 below. Damage to test plants was assessed after 1 4 days on a scale of O to 5 wherein 0 is O to 20% damage and 5 is complete kill. In a test for pre-emergence herbicidal activity, seeds of the test plants were sown in a shallow slit formed in the surface of soil in fibre trays. The surface was then levelled and sprayed, and fresh soil then spread thinly over the sprayed surface. Assessment of herbicidal damage was carried out after 21 days using the same scale of O to 5 as the post-emergence test. In both cases the degree of herbicidal damage was assessed by comparison with untreated control plants. The results are given in Table 5 below. A dash (-) means no experiment was carried out.

The names of the test plants were as follows: Mz Maize Ww Winter wheat Rc Rice Br Barley Av Avena fatua Dg Digitaria sanguinalis Al Alopecurus myosuroides St Setaria viridis Ec Echinochloa crus-galli Sh Sorghum halepense Ag Agropyron repens TABLE 5 Com- APPLICATION TEST PLANT pound Method Rate No (kg/ha) Mz Ww Rc Br Av Dg Al St Ec Sh Ag 1 POST 0.8 3 1 4 3 4 3 4 4 4 2 1 1 POST 0.4 3 0 4 2 4 2 3 4 4 1 1 1 POST 0.2 3 0 1 1 2 2 3 3 3 1 0 2 POST 0.4 4 0 3 0 4 0 2 4 2 0 0 2 POST 0.2 4 0 2 0 4 0 2 3 2 1 0 3 POST 0.8 3 1 4 3 4 2 3 4 4 0 3 3 POST 0.4 3 0 3 2 3 1 1 4 4 0 1 4 POST 0.2 3 3 4 4 4 4 4 4 5 4 2 4 POST 0.05 0 1 3 0 2 4 2 3 3 4 0 6 POST 0.4 4 0 4 2 4 0 2 4 4 3 0 6 POST S).2 4 0 2 1 2 0 1 4 4 2 0 7 POST 0.4 4 0 0 0 4 2 3 3 1 0 0

Claims (14)

1. A compound of formula I

wherein: X, which may be the same or different, are independently selected from the group consisting of: halogen; nitro; cyano; C, to C6 alkyl; C1 to C6 alkyl substituted with a substituent selected from the group consisting of halogen, nitro, hydroxy, C, to C6 alkoxy and C, to C6 alkylthio; C2 to C6 alkenyl; C2 to C6 alkynyl; hydroxy; C1 to C6 alkoxy; C, to C6 alkoxy substituted with a substituent selected from halogen and C, to C6 alkoxy; C2 to C6 alkenyloxy; C2 to C6 alkynyloxy; C2 to C6 alkanoyloxy; (C, to C6 alkoxy)carbonyl; C, to C6 alkylthio; C, to C6 alkylsulfinyl; C, to C6 alkylsulfonyl; sulfamoyl; N-(C, to C6 alkyl) sulfamoyl;N,N-di(C, to C6 alkyl)sulfamoyl; benzyloxy; substituted benzyloxy wherein the benzene ring is substituted with from one to three substituents selected from the group consisting of halogen, nitro, C, to C6 alkyl, C, to C6 alkoxy and C, to C6 haloalkyl; the group NR5R6 wherein R5 and R6 are independently selected from the group consisting of hydrogen, C to C6 alkyl, C2 to C6 alkanoyl, benzoyl and benzyl; the groups formyl and C2 to C6 alkanoyl and the oxime, imine and Schiff base derivatives thereof; R' is selected from the group consisting of: hydrogen; C, to C6 alkyl; C2 to C6 alkenyl;C2 to C6 alkynyl; substituted C, to C6 alkyl wherein the alkyl group is substituted with a substituent selected from the group consisting of C, to C6 alkoxy, C, to C6 alkylthio, phenyl and substituted phenyl wherein the benzene ring is substituted with from one to three substituents selected from the group consisting of halogen, nitro, cyano, C, to C6 alkyl, C, to C6 haloalkyl, C, to C6 alkoxy and C, to C6 alkylthio; C, to C6 alkylsulfonyl; benzenesulfonyl; substituted benzenesulfonyl wherein the benzene ring is substituted with from one to three substituents selected from the group consisting of halogen, nitro, cyano, C1 to C6 alkyl, C, to C6 haloalkyl; C, to C6 alkoxy and C, to C6 alkylthio; an acyl group; and an inorganic or organic cation; R2 is selected from the group consisting of:C, to C6 alkyl; C2 to C6 alkyl; C2 to C6 haloalkenyl; C2 to C6 alkynyl; C2 to C6 haloalkynyl; substituted C, to C6 alkyl wherein the alkyl group is substituted with a substituent selected from the group consisting of halogen, C, to C6 alkoxy, C, to C6 alkylthio, phenyl and substituted phenyl wherein the benzene ring is substituted with from one to three substituents selected from the group consisting of halogen, nitro, cyano, C, to C6 alkyl, C, to C6 haloalkyl, C1 to C6 alkoxy and C, to C6 alkylthio; R3 is selected from the group consisting of: C, to C6 alkyl, C, to C6 fluoroalkyl; C2 to C6 alkyl; C2 to C6 alkynyl; and phenyl; and n is an integer chosen from 1 to 5.

2. A compound according to claim 1 wherein: X, which may be the same or different, are independently selected from the group consisting of: halogen; nitro; cyano; C, to C6 alkyl; C, to C6 alkyl substituted with a substituent selected from the group consisting of halogen, nitro, hydroxy, C, to C6 alkoxy and C, to C6 alkylthio; C2 to C6 alkenyl; C2 to C6 alkynyl; hydroxy; C, to C6 alkoxy; C, to C6 alkoxy substituted with a substituent selected from halogen and C, to C6 alkoxy; C2 to C6 alkenyloxy; C2 to C6 alkynyloxy; C2 to C6 alkanoyloxy; (C, to C6 alkoxy)carbonyl; C, to C6 alkylthio; C, to C6 alkylsulfinyl; C, to C6 alkylsulfonyl; sulfamoyl;N-(C, to C6 alkyl)sulfamoyl; N,N-di(C, to C6 alkyl)sulfamoyl; benzyloxy; substituted benzyloxy wherein the benzene ring is substituted with from one to three substituents selected from the group consisting of halogen, nitro, C, to C6 alkyl, C, to C6 alkoxy and C, to C6 haloalkyl; the group NR5R6 wherein R5 and R6 are independently selected from the group consisting of hydrogen, C, to C6 alkyl, C2 to C6 alkanoyl, benzoyl and benzyl; the groups formyl and C2 to C6 alkanoyl; and the groups of the formula -C(R7) = NR8 wherein R7 is chosen from hydrogen and C, to C6 alkyl, and R8 is chosen from hydrogen, C, to C6 alkyl, phenyl, benzyl, hydroxy, C, to C6 alkoxy, phenoxy and benzyloxy; R' is selected from the group consisting of: hydrogen; C, to C6 alkyl; C2 to C6 alkenyl;C2 to C6 alkynyl; substituted C, to C6 alkyl wherein the alkyl group is substituted with a substituent selected from the group consisting of C, to C6 alkoxy, C, to C6 alkylthio, phenyl and substituted phenyl wherein the benzene ring is substituted with from one to three substituents selected from the group consisting of halogen, nitro, cyano, C, to C6 alkyl, C, to C6 haloalkyl, C, to C6 alkoxy and C, to C6 alkylthio; C, to C6 alkylsulfonyl; benzenesulfonyl; substituted benzenesulfonyl wherein the benzene ring is substituted with from one to three substituents selected from the group consisting of halogen, nitro, cyano, C, to C6 alkyl, C, to C6 haloalkyl, C, to C6 alkoxy and C, to C6 alkylthio;C2 to C6 alkanoyl; benzoyl, substituted benzoyl wherein the benzene ring is substituted with from one to three substituents chosen from the group consisting of halogen, nitro, cyano, C, to C6 alkyl, C, to C6 haloalkyl, C, to C6 alkoxy and C, to C6 alkylthio; 2-furoyl; 3furoyl; 2-thenoyl; 3-thenoyl; and an organic or inorganic cation selected from the alkali metal ions, the alkaline earth metal ions, the transition metal ions and the ammonium ion R9R'0R"R'7N+ wherein R9, R'O, R" and R12 are independently selected from the group consisting of: hydrogen;C, to C,O alkyl; substituted C, to C,O alkyl wherein the alkyl group is substituted with a substituent selected from the group consisting of hydroxy, halogen and C, to C6 alkoxy; phenyl; benzyl; and the groups substituted phenyl and substituted benzyl wherein the benzene ring is substituted with from one to three substituents selected from the group consisting of halogen, nitro, cyano; C, to C6 alkyl, C, to C6 haloalkyl, C, to C6 alkoxy and C, to C6 alkylthio; R2 is selected from the group consisting of:C, to C6 alkyl; C2 to C6 alkenyl; C2 to C6 haloalkenyl; C2 to C6 alkynyl; C2 to C6 haloalkynyl; substituted C, to C6 alkyl wherein the alkyl group is substituted with a substituent selected from the group consisting of halogen, C, to C6 alkoxy, C, to C6 alkylthio, phenyl and substituted phenyl where in the benzene ring is substituted with from one to three substituents selected from the group conssiting of halogen, nitro, cyano, C, to C6 alkyl, C1 to C6 haloalkyl, C, to C6 alkoxy and C, to C6 alkylthio; R3 is selected from the group consisting of: C, to C6 alkyl; C, to C6 fluoroalkyl; C2 to C6 alkenyl; C2 to C6 alkynyl; and phenyl; and n is an integer selected from 1 to 5.

3. A compound according to claim 1 or claim 2 wherein: X are independently selected from the group consisting of C, to C6 alkyl, C, to C6 alkoxy, C, to C6 alkylthio, halogen and C2 to C6 alkanoyl; R' is selected from the group consisting of hydrogen, alkali metal, ammonium, C, to C,O alkylammonium, C2 to C6 alkanoyl, benzoyl and substituted benzoyl wherein the benzene ring is substituted with from one to three substituents selected from the group consisting of halogen, nitro and cyano; R2 is selected from the group consisting of methyl, ethyl, n-propyl, allyl and propargyl; R3 is selected from the group consisting of methyl, ethyl and n-propyl; and n is an integer selected from 1 to 5.

4. A compound according to any one of claims 1 to 3 inclusive wherein: X are independently selected from the group consisting of C, to C6 alkyl, C, to C6 alkoxy, C, to C6 alkylthio and C2 to C6 alkanoyl; R' is selected from hydrogen and C2 to C6 alkanoyl; R2 is selected from ethyl and allyl; R3 is selected from ethyl and n-propyl; and n is an integer selected from 1 to 5.

5. A compound according to any one of claims 1 to 4 inclusive of formula

wherein: X2, X4 and X6 are methyl; X is selected from methyl and acetyl; R1 is hydrogen; R2 is selected from ethyl and allyl; R3 is ethyl; and n is selected from zero and the integers 1 and 2.

6. A compound according to any one of claims 1 to 5 inclusive selected from the group consisting of: 2-[1 -(ethoxyimino)propyl]-6-mesityltetrahydropyran-2,4-dione; 2-[1-(ethoxyimino)propyl]-6-(4-methylthiophenyl)tetrahydropyran-2,4-dione; and 2-El -(ethoxymino)propylj-6-(3-acetyl-2, 4, 6-trimethylphenyl)tetrahydropyran-2 , 4-dione.

7. A herbicidal composition comprising as active ingredient a compound as defined according to any one of claims 1 to 6 inclusive and a carrier therefor.

8. A process for severely damaging or killing unwanted plants which process comprises applying to said plants, or to the growth medium of said plants, an effective amount of a compound as defined according to any one of claims 1 to 6 inclusive or an effective amount of a composition as defined according to claim 7.

9. A process for selectively controlling the growth of monocotyledonous weeds in dicotyledonous crops which process comprises applying to said crop, or to the growth medium of said crop, a compound as defined according to any one of claims 1 to 6 inclusive or a composition as defined according to claim 7 in an amount sufficient to severely damage or kill said weeds but insufficient to substantially damage said crop.

10. A process according to claim 8 or claim 9 wherein the compound is applied at a rate in the range of from 0.005 to 20 kilograms per hectare.

11. A process for the synthesis of a compound of formula I as defined according to any one of claims 1 to 6 inclusive which process comprises: reacting a 3-acyl-6-(aryl) tetrahydropyran-2,4-dione derivative of formula Xl with an alkoxyamine derivative of formula XII to give a compound of the invention of formula II or reacting the 3acyl-6-(aryl) tetrahydropyran-2,4-dione derivative of formula Xl with hydroxylamine and alkylating the oxime intermediate of formula XIII with an alkylating agent of formula XIV, wherein L is a leaving group, to give a compound of the invention of formula II:

and, optionally, reacting the compound of the invention of formula II with a compound of formula XV, wherein L is a leaving group, to give a compound of the invention of formula I.

RL xv

1 2. A compound of formula I as defined according to any one of claims 1 to 6 inclusive substantially as herein described with reference to any one of Examples 1 to 5 inclusive.

1 3. A composition as defined according to claim 7 substantially as herein described with reference to any one of Examples 6 to 9 inclusive.

14. A process as defined according to any one of claims 8 to 10 inclusive substantially as herein described with reference to any one of Examples 7 to 9 inclusive.

1 5. A process as defined according to claim 11 substantially as herein described with reference to any one of Examples 1 to 4 inclusive.