GB2237568A - Herbicidally active substituted ethylidene furanone compounds - Google Patents

Abstract

Compounds of formula <IMAGE> where R<1> represents an optionally substituted amino group; or a silyl group; or a group of formula -OR<4> where R<4> represents a hydrogen atom or an optionally substituted alkyl group; or a divalent metal atom linking two such furan -2,4-dione moieties; or a group of formula -COR<5> where R<5> represents a hydrogen atom or an optionally substituted alkyl, aryl, aralkyl or amino group, or a group of formula -OR<6> where R<6> represents an optionally substituted alkyl, alkenyl or aralkyl group; R<2> represents an alkyl group; and R<3> represents an alkyl group; are novel and show herbicidal activity.

Description

HETEROCYCLIC COMPOUNDS This invention relates to novel heterocyclic compounds, to their use as herbicides, and to their preparation.

According to the present invention there is provided a compound of formula

where R1 represents an optionally substituted amino group; or a silyl group; or a group of formula -OR4 where R4 represents a hydrogen atom or an optionally substituted alkyl group; or a divalent metal atom linking two such furan -2,4-dione moieties; or a group of formula -COR5 where R5 represents a hydrogen atom or an optionally substituted alkyl, aryl, aralkyl or amino group, or a group of formula -OR6 where R6 represents an optionally substituted alkyl, alkenyl or aralkyl group; R2 represents an alkyl group; and R3 represents an alkyl group.

In general terms it may be stated that, unless otherwise specified herein: an alkyl group, including the alkyl linkage of an aralkyl group, suitably has 1-6, especially 1-4, carbon atoms; an alkenyl group suitably has 2-6, especially 2-4, carbon atoms; an optionally substituted alkyl group may suitably be substituted by one or more moieties independently selected from halogen atoms and C16 alkoxy, C1~6 alkythio, and optionally substituted phenyl groups; an optionally substituted aryl group, including the aryl moiety of an aralkyl group, may suitably be substituted by one or more moieties independently selected from halogen atoms and nitro, cyano, C16 alkyl, C1~6 haloalkyl, C16 alkoxy, C16 haloalkoxy and C1-6 6 alkylthio groups.An optionally substituted amino group may suitably be substituted by 1 or 2 (preferably 1) moieties independently selected from amino, hydroxy, alkoxy, alkyl, optionally substituted phenyl groups, alkylsulphonyl and optionally substituted phenylsulphonyl groups Preferably, R2 represents a methyl group.

Preferably, R3 represents a methyl group.

R1 may suitably represent an optionally substituted amino group, for example an amino group optionally substituted by an alkyl group. R1 may desirably represent an unsubstituted amino group.

R1 may suitably represent a silyl group, suitably a trialkylsilyl group. A preferred trialkylsilyl group is tri-isopropylsilyl.

R1 may suitably represent a group of formula -OR4 where R4 represents a hydrogen atom or an alkyl, suitably methyl group.

R1 may suitably represent a copper atom which links two such furan-2,4-dione moieties.

R1 may suitably represent a group of formula -COR5 where R5 may represent a hydrogen atom, an alkyl or haloalkyl group an optionally substituted phenyl group or an optionally substituted amino group, suitably an amino group optionally substituted by one moiety selected from alkyl, phenyl or phenylsulphonyl groups; or R5 may represent a group of formula -oR6.

R6 may represent an alkyl or haloalkyl group, an alkenyl group, or an optionally substituted benzyl group, suitably a benzyl group or alkoxy-substituted benzyl group.

Preferred as R5 is a hydrogen atom, an alkyl group, or a phenylamino group.

Preferred as R1 is a group -COR5 as identified in the previous paragraph, or a trialkylsilyl group, or a copper atom linking two such furan-2,4-dione moieties, or a hydroxy group.

Compounds of formula I have been found to show activity as herbicides, particularly against broad leaved plants, for example mustard, linseed, soya bean and sugar beet, in post-emergence applications. Accordingly, the invention further provides a herbicidal compoisition comprising a compound of formula I as defined above in association with at least one carrier, and a method of making such a composition, which comprises bringing a compound of formula I into association with at least one carrier.

The invention also provides the use of such a compound or composition according to the invention as a herbicide. Further in accordance with the invention there is provided a method of combating undesired plant growth at a locus by treating the locus with a compound or composition according to the invention. The dosage of active ingredient used may, for example, be from 0.01 to 10 kg/ha, suitably from 0.05 to 4 kg/ha.

A carrier in a composition according to the invention is any material with which the active ingredient is formulated to facilitate application to the locus to be treated, or to facilitate storage, transport or handling. A carrier may be a solid or a liquid, including a material which is normally gaseous but which has been compressed to form a liquid, and any of the carriers normally used in formulating biocidal compositions may be used. Preferably compositions according to the invention contain 0.5 to 95% by weight of active ingredient.

Suitable solid carriers include natural and synthetic clays and silicates, for example natural silicas such as diatomaceous earths; magnesium silicates, for example talcs; magnesium aluminium silicates, for example attapulgites and vermiculites; aluminium silicates, for example kaolinites, montmorillonites and micas; calcium carbonate; calcium sulphate; ammonium sulphate; synthetic hydrated silicon oxides and synthetic calcium or aluminium silicates; elements, for example carbon and sulphur; natural and synthetic resins, for example coumarone resins, polyvinyl chloride, and styrene polymers and copolymers; solid polychlorophenols; bitumen; waxes; and solid fertilisers, for example superphosphates.

Suitable liquid carriers include water; alcohols, for example isopropanol and glycols; ketones, for example acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexenone; ethers; aromatic or araliphatic hydrocarbons, for example benzene, toluene and xylene; petroleum fractions, for example kerosene and light mineral oils; chlorinated hydrocarbons, for example carbon tetrachloride, perchloroethylene and trichloroethane. Mixtures of different liquids are often suitable.

Agricultural compositions are often formulated and transported in a concentrated form which is subsequently diluted by the user before application. The presence of small amounts of a carrier which is a surface-active agent facilitates this process of dilution. Thus preferably at least one carrier in a composition according to the invention is a surfaceactive agent. For example the composition may contain at least two carriers, at least one of which is a surfaceactive agent.

A surface-active agent may be an emulsifying agent, a dispersing agent or a wetting agent; it may be nonionic or ionic. Examples of suitable surface-active agents include the sodium or calcium salts of polyacrylic acids and lignin sulphonic acids; the condensation of fatty acids or aliphatic amines or amides containing at least 12 carbon atoms in the molecule with ethylene oxide and/or propylene oxide; fatty acid esters of glycerol, sorbitol, sucrose or pentaerythritol; condensates of these with ethylene oxide and/or propylene oxide; condensation products of fatty alcohol or alkyl phenols, for example p-octylphenol br p-octylcresol, with ethylene oxide and/or propylene oxide; sulphates or sulphonates of these condensation products; alkali or alkaline earth metal salts, preferably sodium salts, of sulphuric or sulphonic acid esters containing at least 10 carbon atoms in the molecule, for example sodium lauryl sulphate, sodium secondary alkyl sulphates, sodium salts of sulphonated castor oil, and sodium alkylaryl sulphonates such as dodecylbenzene sulphonate; and polymers of ethylene oxide and copolymers of ethylene oxide and propylene oxide.

The compositions of the invention may for example be formulated as wettable powders, dusts, granules, solutions, emusifiable concentrates, emulsions, suspension concentrates and aerosols. Wettable powders usually contain 25, 50 or 75% w of active ingredient and usually contain in addition to solid inert carrier, 3-10% w of a dispersing agent and, where necessary, 0-10% w of stabiliser(s) and/or other additives such as penetrants or stickers. Dusts are usually formulated as a dust concentrate having a similar composition to that of a wettable powder but without a dispersant, and are diluted in the field with further solid carrier to give a composition usually containing 0.5-10% w of active ingredient. Granules are usually prepared to have a size between 10 and 100 BS mesh (1.676 - 0.152 mm), and may be manufactured by agglomeration or impregnation techniques.

Generally, granules will contain 0.5-75% w active ingredient and 0-10% w of additives such as stabilisers, surfactants, slow release modifiers and binding agents.

The so-called dry flowable powders" consist of relatively small granules having a relatively high concentration of active ingredient. Emulsifiable concentrates usually contain, in addition to a solvent and, when necessary, co-solvent, 10-50% w/v active ingredient, 2-20% w/v emulsifiers and 0-20% w/v of other additives such as stabilisers, penetrants and corrosion inhibitors.Suspension concentrates are usually compounded so as to obtain a stable, non-sedimenting flowable product and usually contain 10-75% w active ingredient, 0.5-15% w of dispersing agents, 0.1-10% w of suspending agents such as protective colloids and thixotropic agents, 0-10% w of other additives such as defoamers, corrosion inhibitors, stabilisers, penetrants and stickers, and water or an organic liquid in which the active ingredient is substantially insoluble; certain organic solids or inorganic salts may be present dissolved in the formulation to assist in preventing sedimentation or as anti-freeze agents for water.

Aqueous dispersions and emulsions, for example compositions obtained by diluting a wettable powder or a concentrate according to the invention with water, also lie within the scope of the invention. The said emulsions may be of the water-in-oil or of the oil-inwater type, and may have a thick "mayonnaise" - like consistency.

The composition of the invention may also contain other ingredients, for example other compounds possessing herbicidal, insecticidal or fungicidal properties.

In accordance with a further aspect of the present invention there is provided a process for the preparation of a compound of formula I, which comprises one of the following: (A) When a compound of formula I is required, wherein R1 represents a silyl group, treating a compound of formula

with n-buty lithium, followed by addition of a silyl halide. Suitably these procedures are carried out under cooling, in the presence of an inert organic solvent, for example an ether.A temperature in the range -50 to -1000C may suitably be employed, though the reaction mixture may be permitted to rise above this range towards the end. A silyl chloride is preferably employed; (B) When a compound of formula I is required wherein R1 is a formyl group, treating a compound of formula II with n-butyl lithium followed by N-formylimidazole.The reaction conditions may be as described under (A) above; (c) When 2 /compound of formula I is required, wherein R1 represents an optionally substituted amino group, or a hydroxyl group, or an optionally substituted alkoxy group, treating a compound of formula

with a compound of formula R2C(0R7)3 where R2 is as defined above and R7 represents an alkyl group, and reacting the resulting compound with optionally substituted hyrazine, hydroxylamine or an alkyl hydroxylamine, as appropriate, or an acid addition salt thereof.Suitably each step takes place at a temperature in the range t to 500C, conveniently at ambient temperature, in the presence of an inert solvent, which may, for example, be an alcohol or a halogenated hydrocarbon; (D) When a compound for formula I is required, wherein R1 represents a group of formula -COR5 as defined above, except that R5 may not be hydrogen, treating a compound of the general formula II with n-butyl lithium, followed by addition of a halide compound R5-COHal. The reaction conditions may be as described under (A) above.

The moiety Hal is preferably a chlorine atom; (E) When a compound of formula I is required, wherein R1 represents a group of formula -COR5 as defined above, except that R5 may not be hydrogen or a group of formula -OR6, treating a compound of formula II with an anhydride of formula (R5CO)2O. Suitably this reaction takes place at elevated temperature, for example 70-1200C, in an inert atmosphere. The reaction mixture suitably comprises a small amount of a concentrated mineral acid; (F) When a compound of formula I is required, wherein R1 represents a divalent metal atom linking two such furan-2,4-dione moieties, treating a compound of formula I as drawn above wherein R1 represents a hydrogen atom, with a metal salt complexing agent.Suitably, such a reaction may take place at a moderate or moderately elevated temperature, for example 10-600C.

Compounds of formula II and III are known, being disclosed for example in Botanical Gazz., 112, p.525 1951 and in Chem. Pharm. Bull. 27(8) p. 1901-1906 (1979).

The invention is further illustrated by the following examples.

Exam IL Preparaion of 3-[1-(methoxycarbonyl)amino]ethylidene-5 methyl-@@ran-2,4-dione To a suspension of 3-(1-amino)ethylidene-5 methyl-ran-2,4-dione (0.5g) in dry tetrahydrofuran (15ml) a@ -780C under a nitrogen atmosphere was added n-butyl l@thium (1.4ml) dropwise with rapid stirring.

The re@tion mixture was stirred at -780C for 30 minutes and than treated at -780C with a solution of methyl chloroformate (0.3g) in tetrahydrofuran (1ml). The reaction mixture was then allowed to warm up to room tempera@ure, then poured into 2M hydrochloric-acid (10ml) and extracted with diethyl ether (3 x 10ml). The combime@ extracts were dried using magnesium sulphate and the soswee@t was removed in vacuo. The crude product was purifi@@ by column chromatography eluting with diethyl ether/hexane (1/1, v/v) to give the title compound as a white @@@id. Yield: 0.27g. mp. 112-1160C.

Analysi@ -Calc % : C 50.7 H 5.2 N 6.6 Found % : C 50.6 H 5.3 N 6.8 Example 22 Preparation of 3-[1-(acetylamino)]ethylidene-5-methyl furan-@,@-dine A mixture of 3-(1-amino)-ethylidene-5-methylfuram-T,4-dione (0.4g) any acetic anhydride (5ml) were treate@ with 0.lml conc. sulphuric acid and heated under nitragen at 100 C for 4 hours. The remaining acetic anhydrid@@ was removed in vacuo and the crude product was dissaiwd in ethyl acetate/diethyl ether (1/1, v/v), the solution filtered through a pad of silica and the solvent removed, to give the title compound as a white solid.

Yield: 0.36g.

mp. 72-750C.

Analysis: Calc. % : C 54.8 H 5.6 N 7.1 Found % : C 54.3 H 5.6 N 7.3 Examples 3 - 15 Following procedures similar to those described in the foregoing Examples 1 or 2, the further compounds presented in Table 1 below were prepared. In the Table, the compounds are described by reference to the substituents in the general formula I, as stated above. TABLE 1 (COMPOUNDS OF FORMULA 1

Ex. R1 R2 R3 Analysis CHN Other Calc. % Found % 3 COOCH2C6H5 CH3 CH3 62.3 5.2 4.8 oil 62.0 5.4 4.6 4 COO-t-Bu CH3 CH3 oil 5. COOCH2OCl3 CH3 CH3 36.5 3.0 4.2 oil 36.6 3.2 4.1 6. CONHSO2C6H5 CH3 CH3 49.7 4.1 8.3 mp. 155-160 C 49.3 4.1 8.2 (decomp) 7. COO-n-Bu CH3 CH3 56.4 6.7 5.5 oil 57.6 7.0 5.6 8. COOCH2CH2Cl CH3 CH3 46.7 4.3 6.0 oil 43.3 4.3 5.1 9. CONH-i-Pr CH3 CH3 55.0 6.7 11.7 M+H 241 56.2 7.3 11.6 10. CO-C6H4-2[CH2-O-CO-C6H5] CH3 CH3 67.2 4.9 3.6 mp. 129-131 C 67.2 4.9 3.6 M+H 394 11. CO-NH-C6H5 CH3 CH3 M+H 275 12. COOCH2 # CH3 CH3 70.0 5.0 3.7 white foam 69.8 5.1 3.7 TABLE 1 (COMPOUNDS OF FORMULA 1) Ex. R1 R2 R3 Analysis CHN Other Calc. % Found % 13. COOCH2-C6H4-(4-OCH3) CH3 CH3 60.2 5.3 4.4 oil 60.3 5.4 4.2 14. COOOH2CH=CH CH3 CH3 55.2 5.4 5.8 oil 55.6 5.6 5.5 15. COOCl3 CH3 CH3 Further examples were prepared as follows: Example 16 Preparation of 3-( i-formylamino)ethylidene-5-methyl- furan-2 , 4-dione n-Butyl lithium (3ml) was added dropwise at -780C to a stirred suspension of 3-(1-amino)ethylidene-5methyl-furan-2,4-dione (1. 16g) and N-formylimidazole (0.72g) in tetrahydrofuran (25ml). The suspension was stirred at -780C for 1 hour. Tlc indicated no reaction.

The reaction mixture was permitted to warm up to ambient temperature, poured into dilute hydrochloric acid and extracted into ethyl acetate. Chromatography in diethyl ether yielded the title compound as a pale yellow material which formed a semi-solid. Yield was 120mg.

M+H. 1840C.

Analysis: Calc % : C 55.0 H 6.7 N 11.7 Found % : C 56.2 H 7.3 N 11.6 Example 17 Preparation of 3-fl-(tri-isopropvlsilyl)amino]-ethylidene- 5-methyl-furan-2,4-dione n-Butyl lithium (2ml) was added at -780C to a suspension of 3-(i-amino)ethylidene-5-methyl-furan-2,4- dione (0.78g) in tetrahydrofuran (20ml). The temperature was maintained at -780C. After 1 hour triisopropylsilychloride (0.77g) in 10ml tetrahydrofuran was added at -780C. The reaction mixture was kept at -780C for 1 hour then allowed to warm up to OOC. It was then poured into ice cold 2M hydrochloric acid (100ml) and diethyl ether (1BOml) and extracted into diethyl ether.

The diethyl ether extracts were filtered through silica gel. Following column chromatography eluting with diethyl ether components 2-4 were evaporated down on Kugelruhr, at 500C and 0.1mm Hg pressure (13pa), in order to remove tri-isopropylsilylchloride. The residue was crystallised and tested by NMR analysis which confirmed it as the title compound. Yield 0.2g. M+H 312.

Example 18 Preparation of 3- (1-hydroxylamino ) ethylidene-5-methyl- furan-2, 4-dione To a suspension of 5-methyl tetronic acid (3g) in dichloromethane (25ml) was added triethyl orthoacetate (4.47g) in one portion. The reaction mixture was stirred at ambient temperature for 1 hour. A solution of the hydrochloride salt of hydroxylamine (1.8g) and triethylamine (3.6ml) in ethanol (30ml) was added in one portion. The reaction mixture was stirred at ambient temperature for 2 hours. The reaction mixture was pre-absorbed onto silica and chromatographed using diethyl ether. Following work up the title compound (0.27g) was a white solid. mp. 155-1570C.

Analysis: Calc. % : C 49.1 H 5.2 N 8.2 Found % : C 49.4 H 5.3 N 8.1 Example 19 Preparation of 3- (1-hydrazino ) ethylidene-5-methyl-furan- 2,4-dione To a solution of 5-methyl tetronic acid (1.0g) in dichloromethane (25ml) was added triethylorthoacetate (2.0g) in one portion. The reaction mixture was stirred at ambient temperature for 2 hours. Anhydrous hydrazine (0.3g) was added in one portion and the reaction mixture was stirred at ambient temperature for 2 hours. The solvent was removed in vacuo and the crude product purified by recrystallisation from ethanol-ether to give the title compound as a pale yellow solid. mp. 1821840C. Yield 0.52g.

Analysis: Calc. % : C 49.4 H 5.9 N 16.5 Found % : C 49.4 H 6.1 N 16.9 Example 20 Preparation of 3-[1-(methoxyamino)ethylidene]-5-methylfuran-2 , 4-dione To a solution of 5-methyltetronic acid (1.Og) in dichloromethane (25ml) was added triethyl orthoacetate (2.0g) in one portion. The reaction mixture was stirred at ambient temperature for 2 hours. A solution of hydrochloride salt of o-methyl hydroxylamine and triethylamine (1.8ml) in ethanol (20ml) was added in one portion. The reaction was stirred at ambient temperature for 1 hour and the solvent removed in vacuo. The crude product was purified by column chromatography eluting with ethyl acetate to give the title compound as a viscous oil. Yield 0.8g.

Analysis: Calc. % : C 51.9 H 5.9 N 7.6 Found % : C 51.7 H 6.0 N 7.3 Example 21 Preparation of copper complex of 3(l-amino)ethylidene-5 methylfuran-2,4-dione

To a solution of 3-(1-amino)ethylidene-5-methyl furan-2,4-dione (0.5g) in ethanol (2ml) was added a solution of copper (II) acetate monohydrate (0.38g) in ethanol (2ml) and water (2ml). A purple precipitate formed. The reaction mixture was heated at 400C for 10 minutes, cooled and filtered. The crude product was washed with aqueous ethanol (10ml, 1:1 v/v) and dried under vacuum to give the title compound as a purple solid. mp. > 3000C. Yield 0.48g.

Analysis: Calc. % : C 45.2 H 4.3 N 7.5 Found % : C 45.0 H 4.3 N 7.7 Herbicidal Activity To evaluate their herbicidal activity, compounds of formula I according to the invention were tested using as representative range of plants: maize, Zea mays (Mz); rice, Oryza sativa (R); barnyard grass, Echinochloa crusgalli (BG); oat, Avena sativa (0); linseed, Linum usitatissimum (L); mustard, Sinapsis alba (M); sugar beet, Beta vulgaris (SB) and soya bean, Glycine max (S).

The tests fall into two categories, pre-emergence and post-emergence. The pre-emergence tests involved spraying a liquid formulation of the compound onto the soil in which the seeds of the plant specied mentioned above had recently been sown. The post-emergence tests involved two types of test, viz., soil drench and foliar spray tests. In the soil drench tests the soil in which the seedling plants of the above species were growing was drenched with a liquid formulation containing a compound of the invention, and in the foliar spray tests the seedling plants were sprayed with such a formulation.

The soil used in the tests was a prepared horticultural loam.

The formulations used in the tests were prepared from solutions of the test compounds in acetone containing 0.4% by weight of an alkylphenol/ethylene oxide condensate available under the trade mark TRITON X155. These acetone solutions were diluted with water and the resulting formulations applied at dosage levels corresponding to 5kg and lkg of active material per hectare in a volume equivalent to 900 litres per hectare in the soil spray and foliar spray test, and at a dosage of level equivalent to 10 kilograms of active material per hectare in a volume equivalent to approximately 3,000 litres per hectare in the soil drench tests.

In the pre-emergence tests untreated sown soil and in the post-emergence tests untreated soil bearing seedling plants were used as controls.

The herbicidal effects of the test compounds were assessed visually twelve days after spraying the foliage and the soil, and thirteen days after drenching the soil and were recorded on a 0-9 scale. A rating 0 indicates growth as untreated control, a rating 9 indicates death.

An increase of 1 unit on the linear scale approximates to a 10% increase in the level of effect.

The results of the tests are set out in Table 2 below, in which the compounds are identified by reference to the preceding examples. A blank space in Table 2 indicates a rating 0, and the symbol - indicates that testing was not carried out.

TABLE 2 Compound of Soil drench 10kg/ha Dosage Foliar spray Pre-emergence Ex. No. Mz R BG O L M SB S kg/ha Mz R BG O L M SB S Mz R BG O L M SB S 1 5 1 3 6 2 5 1 3 2 4 6 5 6 7 4 7 6 5 2 1 3 4 7 6 4 4 2 4 4 4 7 3 4 2 1 2 5 2 2 2 1 1 3 1 3 4 2 2 5 5 3 4 6 6 6 7 1 2 1 1 2 3 5 2 5 3 4 5 4 1 2 TABLE 2 (continued) Compound of Soil drench 10kg/ha Dosage Foliar spray Pre-emergence Ex. No. Mz R BG O L M SB S kg/ha Mz R BG O L M SB S Mz R BG O L M SB S 5 5 4 5 1 3 5 4 3 1 2 1 6 1 4 2 5 3 5 4 5 2 2 1 5 6 3 4 1 4 2 2 1 3 3 3 2 7 5 3 4 3 6 6 5 6 1 2 4 3 3 3 8 4 5 2 2 4 4 5 5 3 7 2 1 1 1 2 3 1 3 TABLE 2 (continued) Compound of Soil drench 10kg/ha Dosage Foliar spray Pre-emergence Ex. No.Mz R BG O L M SB S kg/ha Mz R BG O L M SB S Mz R BG O L M SB S 9 5 4 5 3 6 2 3 1 2 3 1 10 5 3 3 2 1 1 11 5 5 3 4 5 6 6 4 7 4 3 5 4 7 3 8 4 1 2 2 3 6 3 4 5 1 2 3 1 3 12 2 3 5 2 5 3 2 1 1 1 3 1 TABLE 2 (continued) Compound of Soil drench 10kg/ha Dosage Foliar spray Pre-emergence Ex. No. Mz R BG O L M SB S kg/ha Mz R BG O L M SB S Mz R BG O L M SB S 13 6 5 4 4 6 3 4 6 5 4 2 4 5 5 3 5 1 1 4 1 2 14 5 4 2 3 3 5 4 4 1 2 2 2 2 16 - - - - - - - - 5 6 4 6 6 8 5 6 8 6 6 7 6 8 8 8 4 1 - - - - - - - - - - - - - - - 17 6 5 7 6 7 6 6 7 5 5 5 6 6 7 6 6 7 5 5 7 6 7 6 8 6 1 3 2 3 5 6 5 5 7 3 2 4 4 5 5 7 TABLE 2 (continued) Compound of Soil drench 10kg/ha Dosage Foliar spray Pre-emergence Ex. No. Mz R BG O L M SB S kg/ha Mz R BG O L M SB S Mz R BG O L M SB S 18 5 4 5 5 6 4 5 5 5 6 2 5 4 6 4 4 5 2 1 4 4 7 4 3 2 (after 13) 1 2 1 2 6 1 3 4 1 1 1 3 days) 18 7 6 7 7 7 6 7 7 5 7 3 7 5 8 6 5 7 5 4 7 5 7 4 5 5 (after 19 1 3 1 3 3 7 2 3 5 4 4 1 2 1 days) 19 1 5 5 4 4 1 5 3 5 5 6 7 4 4 1 2 5 3 1 4 6 6 3 3 2 1 20 2 3 2 3 5 1 3 3 3 2 1 2 3 1 1 1 2 TABLE 2 (continued) Compound of Soil drench 10kg/ha Dosage Foliar spray Pre-emergence Ex. No. Mz R BG O L M SB S kg/ha Mz R BG O L M SB S Mz R BG O L M SB S 21 8 7 8 6 8 6 6 8 5 7 7 8 6 8 7 8 6 8 7 8 8 8 8 8 7 1 5 5 5 5 7 2 5 4 5 4 6 5 6 3 5 2

Claims (13)

1. CLAIMS 1. A compound of formula

   where R1 represents an optionally substituted amino group; or a silyl group; or a group of formula -OR4 where R4 represents a hydrogen atom or an optionally substituted alkyl group; or a divalent metal atom linking two such furn -2,4-dione moieties; or a group of formula -COR5 where R5 represents a hydrogen atom or an optionally substituted alkyl, aryl, aralkyl or amino group, or a group of formula -OR6 where R6 represents an optionally snbstituted alkyl, alkenyl or aralkyl group; R2 represents an alkyl group; and R3 represents an alkyl group.
2. 2. A compound as claimed in Claim 1, wherein R2 represents a methyl group.
3. 3. A expound as claimed in Claim 1 or 2, wherein R3 represents a methyl group.
4. 4. A compound as claimed in any of Claims 1 to 3, wherein R1 represents a tri-alkylsilyl group.
5. 5. A Compound as claimed in any of Claims 1 to 3, wherein R1 represents a hydroxy group.
6. 6. A compound as claimed in any of Claims 1 to 3, wherein R1 represents a copper atom linking two such furan-2 , 4-dione moieties.
7. 7. A compound as claimed in any of Claims 1 to 3, wherein R1 represents a group of formula -COR5 where R5 represents a hydrogen atom, an alkyl group or a phenylamino group.
8. 8. A process for the preparation of a compound of formula I, as claimed in any preceding claim, which comprises one of the following: (A) When a compound of formula I is required, wherein R1 represents a silyl group, treating a compound of formula

   with n-butyl lithium, followed by addition of a silyl halide.

   (B) When a compound of formula I is required wherein R1 is a formyl group, treating a compound of formula II with n-butyl lithium followed by N-formylimidazole.

   (C) When a compound of formula I is required, wherein R1 represents an optionally substituted amino group, a hydroxyl group, or an optionally substituted alkoxy group, treating a compound of formula

   with a compound of formula R2C(oR7)3 where R2 is as defined above and R7 represents an alkyl group, and reacting the resulting compound with optionally substituted hydrazine, or hydroxylamine or an alkyl hydroxylamine group, as appropriate, or an acid addition salt thereof.

   (D) When a compound for formula I is required, wherein R1 represents a group of formula -COR5 as defined above, except that R5 may not be hydrogen, treating a compound of the general formula II with n-butyl lithium, followed by addition of a halide compound R5-COHal.

   (E) When a compound of formula I is required, wherein R1 represents a group of formula -COR5 as defined above, except that R5 may not be hydrogen or a group of formula -OR6, treating a compound of formula II with an anhydride of formula (R5CO)20.

   (F) When a compound of.4 formula I us required, wherein R1 represents a divalent metal atom linking two such furan-2,4rdione moieties, treating a compound of formula I as drawn above wherein R1 represents a hydrogen atom, will a metal salt complexing agent.
9. 9. A compound of formula I, whenever prepared by a process as claimed in Claim 8.
10. 10. A herbicidal composition comprising a compound of formula I as claimed in any of Claims 1 to 7, or Claim 9, in association with at least one carrier.
11. 11. A method of combating plant growth at a locus by treating the locus with a compound as claimed in any of Claims 1 to 7 or Claim 9, or with a composition as claimed in Claim 10.
12. 12. Use as a herbicide of a compound of formula I, as claimed in any of Claims 1 to 7, or Claim 9.
13. 13. A compound of formula I, or a process for the preparation thereof, as a herbicidal composition, or a method or use, substantially as hereinbefore described with particular reference to the Examples.