GB2284600A

GB2284600A - Herbicidal 3-(hetero)aryl-4-acylisoxazole compositions and compounds

Info

Publication number: GB2284600A
Application number: GB9422682A
Authority: GB
Inventors: Shrikant Sadanand Sakhalkar; Girish Mukund Khandekar; Suhas Dattatraya Sahasrabudhe; Chennupati Koteswara Rao; David Charles Lathbury
Original assignee: SHELL INT RESEARCH; Shell Internationale Research Maatschappij BV
Current assignee: SHELL INT RESEARCH; Shell Internationale Research Maatschappij BV
Priority date: 1994-01-21
Filing date: 1994-11-10
Publication date: 1995-06-14
Also published as: GB9422682D0

Abstract

The invention provides a method of combating undesired plant growth at a locus, comprising applying to the locus a compound of general formula <IMAGE> [where R<1> represents an optionally substituted aryl or heteroaryl group; R<2> represents an optionally substituted alkyl, alkoxy or aryl group; and R<3> represents an optionally substituted alkyl, aryl, amino or amido group, or a group of general formula -COOR<4> (where R<4> represents a hydrogen atom or an optionally substituted alkyl group); or R<2> and R<3> together represent an optionally substituted alkylene chain optionally interrupted in the chain by one or more hetero atoms; provided that R<1> does not represent a phenyl group substituted by a nitro group at the 2-position and by an optionally substituted phenoxy group at the 4-position, when R<2> represents an optionally substituted alkyl or phenyl group and R<3> represents a group of general formula COOR<4>] together with a corresponding herbicidal composition. Certain compounds are novel and these and a process for their preparation are also disclosed.

Description

HERBICIDAL METHODS, COMPOSITIONS AND COMPOUNDS This invention relates to methods of combating undesired plant growth, to herbicidal compositions and to certain novel compounds. The invention employs 3-aryl or 3-heteroaryl-isoxazole compounds.

GB 2201672A discloses certain 2-(3-isoxazolyl and 3thiazolyl)-4-(2'-chloro-4'-trifluoromethylphenoxy)nitrobenzene compounds, and their use as herbicides.

In accordance with a first aspect of the present invention there is provided a method of combating undesired plant growth at a locus, comprising applying to the locus a compound of general formula

where Rl represents an optionally substituted aryl or heteroaryl group; R2 represents an optionally substituted alkyl, alkoxy or aryl group; and R3 represents an optionally substituted alkyl, aryl, amino or amido group, or a group of general formula -COOR4 where R4 represents a hydrogen atom or an optionally substituted alkyl group or R2 and R3 together represent an optionally substituted alkylene chain optionally interrupted in the chain by one or more hetero atoms; provided that R' does not represent a phenyl group substituted by a nitro group at the 2-position and by an optionally substituted phenoxy group at the 4-position, when R2 represents an optionally substituted alkyl, alkoxy or phenyl group and R3 represents a group of general formula -COOR4.

Included within the scope of the present invention are standard derivatives of such compounds such as salts and N-oxides.

Generally, when any of the above mentioned moieties comprises an alkyl group this alkyl group may be linear or branched and may suitably contain 1 to 10, preferably 1 to 6, and most preferably 1 to 4 carbon atoms, suitable examples being methyl, ethyl and propyl. When any groups are designated as being optionally substituted, the substituent groups which are optionally present may be any of those customarily employed in the development of pesticidal compounds, and/or the modification of such compounds to influence their structure/activity, persistence, penetration or other property.In relation to moieties defined above which comprise an optionally substituted alkyl or alkylene group, specific examples of such substituents include halogen, especially fluorine, chlorine or bromine atoms, and nitro, cyano, hydroxyl, Cl4 alkoxy, C haloalkoxy, (C alkoxy)carbonyl groups, amino and 01A alkylamino groups; and, in relation to an alkylene group, oxo groups. It is preferred, however, that alkyl moieties are unsubstituted, or halogen-substituted and that alkylene moieties are unsubstituted, or only substituted by alkyl.In relation to moieties defined above which comprise an optionally substituted aryl or heteroaryl group, optional substituents include halogen, especially fluorine, chlorine and bromine atoms, and nitro, cyano, amino, hydroxyl, Cl4 alkyl, C1A haloalkyl (especially CF3) and C,, alkoxy groups. I to 3 substituents may suitably be employed. An optionally substituted amino or amido group may suitably be mono- or di-substituted by an alkyl group. A halogen atom may most suitably be a fluorine, chlorine or bromine atom. A preferred aryl group is phenyl. A preferred ieteroaryl group is thienyl, especially 2-thienyl. When an alkylene group is interrupted by one or more hetero atoms, those hetero atoms may suitably be selected from nitrogen, oxygen and sulphur.Preferred alkylene chains have one or two hetero chain atoms or, most preferably, none.

Preferably R' represents a phenyl group, optionally substituted by halogen, cyano, nitro, oxyalkyleneoxy or optionally substituted alkyl, alkoxy, phenoxy or benzyloxy.

Preferably Rl represents a phenyl group optionally substituted by one or two moieties independently selected from halogen, alkyl, alkoxy, benzyloxy, haloalkyl, cyano or nitro, or by a group -O-CH2-O-. More preferably, Rl represents a phenyl group optionally substituted by one or two moieties independently selected from halogen, alkoxy, most preferably methoxy and haloalkyl, most preferably trifluoromethyl.

Preferably R' represents a phenyl group which has one substituent at the 4-position relative to the linkage, and optionally, a substituent at the 2-position.

Examples of particularly preferred groups R' are 2,4dichlorophenyl, 4-chiorophenyl, 4-bromophenyl, 4-methoxyphenyl and 4-trifluoromethylphenyl.

Preferably R2 as an independent moiety represents a phenyl, CIA alkyl or CIA alkoxy group; and most preferably, a methyl group.

Preferably, R3 as an independent moiety represents a phenyl or amino group, an alkyl group, most preferably methyl, a group of general formula -COOR4, where R' represents a hydrogen atom or an alkyl, most preferably methyl, group, or an monoalkylamido group.

Most preferably, however, R2 and R3 together represent an optionally substituted alkylene chain, suitably having two or, most preferably, three chain carbon atoms. Preferred examples are -CH2-C(CH3)2-CH2- or, most preferably, -(CH2) In a method as defined above, the dosage of the active ingredient, the compound of general formula I, may, for example, be from 0.01 to 10kg/ha, suitably 0.05 to 4kg/ha.

The locus may be an agricultural or horticultural locus, comprising, for example, a plant or soil. In a preferred method the locus contains undesired plant growth and treatment is by foliar spray application.

The invention also provides the use of a compound as defined above, as a herbicide.

In accordance with a further aspect of the present invention there is provided a herbicidal composition comprising a compound of general formula I as defined above, in association with at least one carrier which is a surface-active agent. Preferably there are at least two carriers, at least one of which is a surface-active agent.

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 pesticidal 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, montomorillonites 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 cyclohexanone; ethers; aromatic or araliphatic hydrocarbons, for example benzene, toluene and xylene; petroleum fractions, for example kerosine 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 surface-active agent. For example the composition may contain at least two carriers, at least one of which is a surface-active 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 products 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, sorbitan, sucrose or pentaerythritol; condensates of these with ethylene oxide and/or propylene oxide; condensation products of fatty alcohol or alkyl phenols, for example - octylphenol or 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, emulsifiable 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 l/2-lOt 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 '/2-75% w active ingredient and 0-10t 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 higher concentration of active ingredient. Emulsifiable concentrates usually contain, in addition to a solvent and, when necessary, cosolvent, 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 antifreeze 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 ot of the oil-in-water type, and may have a thick "tnayonnaise"-like consistency.

Certain compounds defined above are known (but not as herbicidal agents). These include 4-acyl and 4-aroyl isoxazole compounds. One example is methyl 3-(4chlorophenyl) -4-acetylisoxazole - 5-carboxylate (Registry No. 129144-29-2). Of the compounds defined above in which R2 and R3 together represent an optionally substituted alkylene group, the following are believed to be known: 6,6-Dimethyl-3-phenyl~6,7-dihydro-1,2-benzisoxazole-4(5H)- one (Registry No. 53688-80-5) 6, 6-Dimethyl-3- (3-nitrophenyl) -6, 7-dihydro-1, 2- benzisoxazole-4(5H)-one (Registry No. 53688-81-6) 3-(3-nitrophenyl)6,7-dihydro-l, 2-benzisoxazole-4 (5H) -one (Registry No 65924-69-8).

3-(4-Fluorophenyl)-6,7-dihydro-1,2-benzisoxazole-4(5H)-one Registry No. 141926-83-2).

A further aspect of the present invention relates to novel compounds defined or described herein. There is provided a novel class of compounds of general formula I as defined above wherein R' represents a phenyl group which is substituted by halogen, cyano, oxyalkyleneoxy or optionally substituted alkyl, alkoxy, phenoxy or benzyloxy, or is a 2-thienyl group, and R2 and R' together represent an optionally substituted alkylene chain; but not including 3-(4-fluorophenyl)w6, 7-dihydro-1,2 benzisoxazole-4 (5H) -one.

In accordance with a further aspect of the present invention there is provided a process for the preparation of a novel compound of general formula I, which comprises reacting a compound of general formula II with a compound of general formula III

when Hal represents a halogen atom and Rl, R2 and R3 are as defined in the above definition of novel compounds.

Preferably the reaction between the compounds of general formulae II and III is carried out in the presence of an organic solvent, suitably a halogenated hydrocarbon, for example chloroform, or an ether, for example tetrahydrofuran. A base may suitably be present, for example an organic base. Triethylamine is preferred.

There may be an organic base and, additionally, a solvent, but one material could function both as base and solvent.

The reaction is suitably effected at a temperature in the range of 0 to 600C, preferably 15 to 30 C. Work-up of the product may be by standard means. Preferably, Hal represents a bromine or, especially, a chlorine atom.

Compounds of general formulae II and III are known or may readily be prepared from known compounds. One route to compounds of general formula II is to react an aldehyde R'-CHO with hydroxylamine hydrochloride in the presence of pyridine and methanol, under reflux conditions, to produce the corresponding aldoxime R'-CH=N-OH; and to halogenate this, for example, using N-chlorosuccinimide, suitably at ambient temperature, in the presence of dimethylformamide.

The invention will now be further described, by way of Example.

EXAMPLE 1 PreParation of 3-(4-chloronhenvl)-tetrahvdro-1 .2- benzisoxazole-4-one (Rl=4-Cl-Ph, R2R-'-(CH2)3 ).

EXAMPLE la PreParation of 4 -chlorobenzaldoxime A mixture of 4-chlorobenzaldehyde (5 g), hydroxylamine hydrochloride (4.16 g), and pyridine (4.25 ml) in 75 ml of methanol was ref fluxed for 1 hour. The solution was then concentrated, treated with 200 ml of water and cooled in an ice bath. The solid obtained was collected by filtration under suction, washed with 100 ml of 10% hydrochloric acid followed by two 100 ml portions of water and dried thoroughly to yield the title intermediate compound as a white solid (4.9 g). m.p.

115.4 C.

This was characterised by 'H NMR.

EXAMPLE 1b Preparation of 4-chlorobenzhvdroximovl chloride A solution of the product of Example la (5.0 g) in 25 ml of dimethylformamide was stirred at 20-30 C. To this was added N-chlorosuccinimide (4.3 g) in five portions.

After the addition was complete, in 45 minutes, the reaction mixture was further stirred for 2 hours. Water (200 ml) was then added to the reaction mixture and it was extracted with two 100 ml portions of diethyl ether. The combined ethereal extract was then washed with two 100 ml portions of water, dried over anhydrous sodium sulphate and the diethyl ether was stripped off under reduced pressure to yield the intermediate title compound as a white solid (4.9 g), m.p. 88.3"C. This was characterised by 'H NMR.

Elemental analysis: Calculated : C 44.2 H 2.6 N 7.4% Found : C 44.6 H 2.6 N 7.3t EXAMPLE ic PreDaration of 3-(4-ch1orohenvl)-tetrahvdro-1 2benzisoxazole-4-one A solution of 1,3-cyclohexanedione (2.0 g) and triethylamine (10.9 g) in 200 ml chloroform was stirred, cooled at 10-20"C and a solution of the product of Example ib in 250 ml chloroform was added dropwise over a period of two hours. The reaction mixture was stirred for a further 18 hours at ambient temperature. The reaction mixture was washed with two 100 ml portions of 10% hydrochloric acid followed by 100 ml of water. The solution was dried over anhydrous sodium sulphate and the solvent was stripped off under reduced pressure.The residual product was purified by column chromatography over silica gel (60-120 mesh) eluting with chloroform to yield the title compound as a yellowish white solid (1.1 g), m.p. 85.30C. This was characterised by 'H NMR.

'H NMR (CDC13) in ppm 2.1 - 2.8 (4H) (multiplet) 3.1 (2H) (triplet) 7.4 & 8.2 (4H) (AB quartet) Elemental analysis: Calculated : C 63.0 H 4.0 N 5.7 Z Found : C 62.7 H 4.2 N 5.4 Z EXAMPLES 2 - 33 These were prepared in the manner described for Example 1. In some cases with different Rl groups, on treatment of the reaction mixture with water, the oxime separated as a semi-solid or liquid. In such cases the product was extracted with chloroform, washed with 10% hydrochloric acid, followed by water, dried over anhydrous sodium sulphate and the solvent stripped off under reduced pressure to obtain the product. Compound details and analytical data is given in Table 1 below.

The compounds of Table 1 are of the general formula

TABLE 1

Example No. R X M.P. ( C) Elemental Analysis % (Calc/Found) C H N 2 4-OC2H5 H 72.8 70.0 5.9 5.3 68.6 5.8 5.4 3 4-OCH3 H 58.6 69.1 5.3 5.8 68.1 5.5 5.9 4 3-OCH3 H - 69.1 5.3 5.8 68.5 5.5 5.5 5 2-OCH3 H - 69.1 5.3 5.8 67.8 5.5 5.5 6 4-OCH2Ph H 103.0 75.2 5.3 4.4 74.0 5.0 4.5 7 4-CH3 H - 74.0 5.7 6.2 73.4 5.7 6.1 8 H H 70.3 73.2 5.2 6.6 72.7 5.3 6.4 9 4-CF3 H 102.6 59.8 3.6 5.0 59.4 3.5 5.0 10 3-CF3 H 98.3 59.8 3.6 5.0 59.4 3.5 5.0 11 4-Br H 111.2 53.4 3.4 4.8 52.7 3.4 4.8

Example No. R X M.P. ( C) Elemental Analysis % (Calc/Found) C H N 12 3-Cl H 55.1 63.0 4.0 5.7 62.8 4.0 5.7 13 2-Cl H 89.6 63.0 4.0 5.7 62.7 4.0 5.8 14 4-F H - 67.5 4.3 6.1 66.6 4.5 6.1 15 4-CN H 142.3 70.6 4.2 11.8 69.7 4.5 11.8 16 2,6-Cl2 H 186.6 55.3 3.2 5.0 54.4 3.2 4.9 17 3,4# H 113.6 65.6 4.3 5.5 64.2 4.1 5.8 18 2-F,4-CF3 H 100.2 56.2 3.0 4.7 54.9 2.9 4.7 19 4-CH9CH3)2 H - 75.3 6.7 5.5 74.7 7.3 5.9 20 2,4-F2 H - 62.7 3,6 5.6 62.9 3.7 5.7 21 2-NO2 H 128.9 60.5 3.9 10.9 60.2 4.0 10.8 22 2-F H 118.1 67.5 4.3 6.1 66.6 4.3 6.0

Example No. R X M.P. ( C) Elemental Analysis % (Calc/Found) C H N 23 4-O(CH2)2CH3 H 76.5 70.8 6.3 5.2 70.6 6.4 5.6 24 4-O(CH2)3CH3 H 74,7 71.6 6.7 4.9 71.5 6.7 4.8 25 2,4-CL2 H 26 4-OCH3 CH3 105.2 70.8 6.3 5.1 69.8 6.5 4.6 27 4-CH3 CH3 108.2 70.1 7.1 5.1 70.3 7.0 5.1 28 H CH3 - 72.0 6.4 5.6 71.6 6.1 6.0 29 4-Cl CH3 139.2 59.5 5.6 4.6 59.2 5.5 5.1 30 2-F,4-CF3 CH3 58.7 4.0 4.3 59.4 4.2 4.9 31 2,4-Cl2 CH3 110-112 58.0 4.2 4.5 59.4 4.2 5.0 32 4-OPh H 99.2 74.8 4.9 4.6 74.4 5.0 4.5 33 3-OPh H - 74.8 4.9 4.6 74.0 4.9 4.5 EXAMPLE 34 Prenaration of 3-{4-chloronhenYl)-4-acetvl-s- methvlisoxazole (Rl=4-Cl-Ph; R=CH@ ; RCH,) A solution of acetylacetone (1.7 g) and triethylamine (10.3 g) in 200 ml chloroform, was stirred, cooled at 1-0- 200C and a solution of the product of Example lb (3.8 g) in 250 ml chloroform was added dropwise over a period of two hours. The reaction fixture was stirred further for 18 hours at ambient temperature.The reaction mixture was washed with two 200 ml portions of 109 hydrochloric acid followed by 100 ml of water. The solution was dried over anhydrous sodium sulphate, and the solvent was stripped off under reduced pressure. The residual product was purified by column chromatography over silica gel (60-120 mesh) eluting with chloroform to yield the title compound as a yellow oil (1.4 g). This was characterised by i NMR.

1H NMR (CDCl3) in ppm 2.2 (3H) (singlet) 2.7 (3H) (singlet) 7.6 (4H) (singlet) Elemental analysis Calculated: C 61.1 H 4.2 N 5.9 % Found: C 61.1 H 4.3 N 6.0 % EXAMPLE 35 Prenaration of methyl 3-(4-chlorophenyl)-4- acetylisoxazole-5-carboxylate (R'=4-Cl-Ph ; R=ch3 ; R -COOCH3) To a stirred solution of methyl acetopyruvate (4.32 g) and the product of Example Ib (5.7 g) in 120 ml of dry tetrahydrofuran was added dropwise a solution of triethylamine (3.03 g) in 30 ml of dry tetrahydrofuran at 0 C over a period of 2 hours. The reaction mixture was stirred further for 24 hours at ambient temperature. The solution was then filtered and the filtrate was washed with 100 ml of water, dried over anhydrous sodium sulphate and the solvent was stripped off under reduced pressure.

The residual product was purified by column chromatography over silica gel (100-200 mesh) eluting with n-hexane:ethyl acetate (4:1) to yield the title compound as a white solid (2.33 g), m.p. 129.7 C. This was characterised by 'H NMR.

'H NMR (CDC13) in ppm 2.8 (3H) (singlet) 3.6 (3H) (singlet) 7.5 (4H) (singlet) Elemental analysis Calculated: C 55.8 H 3.6 N 5.0 Z Found: C 55.8 H 3.6 N 4.9 Z EXAMPLE 36 Preparation of i-butvl 3-(2-methoxvnhenvl)-4- acetvlisoxazole-5-carboxamide (Rl=2-OCH3-Ph, R2=CH3, R3=CONH-iBu) A solution of methyl 3-(2-methoxyphenyl)-4acetylisoxazole-5-carboxylate (1.0 g) and isobutylamine (0.5 g) in 20 nl of benzene were ref fluxed for 4 hours in a water bath. Water (25 ml) was added to the reaction mixture and it was extracted with two 25 ml portions of chloroform. The combined organic extracts were washed with two 25 ml portions of 10% hydrochloric acid followed by 50 ml of water.The solution was dried over anhydrous sodium sulphate and the solvent was stripped off under reduced pressure to yield the title compound as a yellow solid (0.9 g), m.p. 124.9 C. This was characterised by 'H NMR.

1H (CDC13) in ppm 0.9 (6H) (doublet) 1.5 (1H) (multiplet) 2.6 (3H) (singlet) 3.1 (2H) (triplet) 3.7 (3H) (singlet) 7.0-8.0 (4H) (multiplet) Elemental analysis Calculated: C 64.6 H 6.3 N 8.9 Z Found: C 64.6 H 6.5 N 8.9 Z EXAMPLE 37 PreDarationof3-2.4-dichlorophenvl)-4-acetvlisoxazole-5- carboxylic acid (Rl=2,4-Cl2-Ph, R2=CH3, R3=COOH) A solution of potassium hydroxide (1.4 g) in a mixture of 5 ml water and 10 ml methanol was added dropwise to a solution of methyl 3-(2,4-dichlorophenyl)-4acetylisoxazole-5-carboxylate (2.5 g) in 10 ml methanol with stirring. The reaction mixture was stirred for 2 hours at ambient temperature. Water (20 ml) was added and the reaction mixture was extracted with chloroform.The organic extract was washed with 25 ml of 10% hydrochloric acid followed by 25 ml of water. The solution was dried over anhydrous sodium sulphate and the solvent was stripped. off under reduced pressure to yield the title compound as- a reddish brown semi-solid (1.8 g). This was characterised by 1H NMR.

1H NMR (CDC13) in ppm.

2.2 (3H) (singlet) 7.2-7.7 (3H) (multiplet) Elemental analysis Calculated: C 48.0 H 2.3 N 4.7 z Found: C 46.9 H 2.3 N 4.9 Z EXAMPLES 38 TO 67 These were prepared in the manner described above.

Compound details and analytical data are given in Table 2 below. The compounds of Table 2 are of the general formula

TABLE 2

Example No. R R R M.P. ( C) Elemental Analysis % (Calc/Found) C H N 38 4-OCH3 CH3 CH3 - 67.5 5.6 6.1 67.0 5.6 6.2 39 4-CF3 CH3 CH3 - 58.0 3.7 5.2 57.6 3.7 5.3 40 4-Br CH3 CH3 - 51.4 3.6 5.0 51.5 3.6 5.0 41 3-Cl CH3 CH3 - 61.1 4.2 5.9 60.7 4.2 5.8 42 4-F CH3 CH3 - 65.8 4.6 6.4 65.1 4.5 7.2 43 2,4-Cl2 CH3 CH3 - 53.3 3.3 5.2 53.2 3.4 5.2 44 4-OCH3 Ph CH3 - 73.7 5.2 4.8 72.5 5.2 4.7 45 4-CF3 Ph CH3 - 65.3 3.6 4.2 65.0 3.6 4.1 46 4-CF3 Ph Ph 127.9 70.2 3.6 3.6 70.0 3.6 3.5 47 4-OCH3 CH3 COOCH3 218.6 61.1 4.7 5.1 60.1 4.7 5.1 48 4-Br CH3 COOCH3 134.2 48.1 3.1 4.3 48.0 3.1 4.3 49 2,4-Cl2 CH3 COOCH3 - 49.7 2.9 4.5 48.9 2.9 4.4

Example R R R M.P. ( C) Elemental Analysis % No. (Calc/Found) C H N 50 2-F,4-CF3 CH3 COOCH3 - 50.8 2.7 4.2 50.3 2.8 4.1 51 2-OCH3 CH3 COOCH3 112.2 61.1 4.7 5.1 60.2 4.7 5.0 52 4-OC2H3 CH3 COOCH3 96.7 62.3 5.2 4.8 62.5 5.2 5.2 53 3-OCH3 CH3 COOCH3 56.8 61.1 4.7 5.1 60.4 4.7 5.3 54 4-Cl OCH3 NH2 139.4 52.3 3.6 11.1 53.0 3.9 10.7 55 4-Br CH3 COOH - 46.5 2.6 4.5 45.9 2.7 4.6 56 2-OCH3 CH3 COOH 135.0 57.8 4.4 5.2 57.6 4.3 5.0 57 4-OC2H5 CH3 COOH - 61.1 4.7 5.1 60.6 5.2 5.9 58 2-OCH3 CH3 CONHC2H5 127.0 60.6 5.7 9.4 60.3 5.5 8.9 59 2-F,4-CF3 CH3 CONHC2H5 99.3 52.3 3.5 8.1 51.8 3.5 7.8 60 2,4-Cl2 CH3 CONHC2H5 95.7 51.3 3.7 8.6 50.9 3.7 8.5 61 4-OC2H5 CH3 CONHC2H5 - 63.6 6.0 9.3 60.9 6.2 8.7

Example R R R M.P. ( C) Elemental Analysis % No. (Calc/Found) C H N 62 4-Cl CH3 CONHC2H5 94.7 57.4 4.4 9.6 57.7 4.6 9.6 63 2-F,4-CF3 CH3 CONH-iBu 96.1 54.8 4.3 7.5 54.2 4.0 7.5 64 4-OC2H5 CH3 CONH-iBu 125.3 65.5 6.7 8.5 65.3 6.7 8.4 65 3-OCH3 CH3 CONH-iBu - 64.5 6.4 8.9 65.4 6.7 8.6 66 2-F,4-CF3 CH3 CONH-iPr 75.3 53.8 3.9 7.8 53.1 3.9 7.5 67 3-OPh CH3 CH3 - 73.7 5.1 4.8 73.6 5.1 4.8 EXAMPLE 68 3-(2-Thienyl)-tetrahydro-1,2-benzisoxazole-4-one (R'=2-thienyl, RR =(CH2)3) m.p. 105.80C.

Elemental analysis: Calculated: C 60.3 H 4.1 N 6.4 Z Found: C 59.9 H 4.1 N 6.2 Z Herbicidal Activity To evaluate their herbicidal activity, compounds of formula I according to the invention were tested using a representative range of plants: maize, Zea mavs (Z); rice, Orvza sativa (R); barnyard grass, Echinochloa crusaalli (G); oat, Avena sativa (0); linseed, Linum usitatissimum (L); mustard, Sinansis alba (M); sugar beet, Beta vulaaris (B) 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 species 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 0.4t by weight of an alkylphenol/ethylene oxide condensate available under the trade mark TRITON X-155. 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 600 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 3 below. A blank space in Table 3 indicates a rating 0.

The symbol * denotes that no result was obtained.

TABLE 3

Compound Soil drench 10 Kg/ha Dosage Foliar Spray Pre-emergence of of kg/ha Ex. No. Z R G O L M B S Z R G O L N B S Z R G O L M B S 1 6 8 7 6 5 8 8 9 9 8 8 9 8 1 7 6 9 7 6 5 8 7 2 5 4 8 4 8 4 5 1 3 6 2 7 2 2 3 2 3 4 5 7 6 9 8 6 8 9 8 2 1 6 3 8 7 3 4 5 8 2 4 5 3 8 4 2 4 7 4 1 2 2 2 2 2 2 5 5 6 7 1 2 6 5 7 1 5 3 2 2 6 6 5 5 8 4 6 7 9 5 1 2 6 2 2 5 7 2 7 5 5 5 9 6 6 8 7 6 1 3 2 2 3 1 1 4 3 8 5 4 6 5 4 4 6 6 5 1 2 4 2 2 2 1 2 2 9 5 5 5 5 2 1 4 5 8 5 9 8 7 8 9 8 6 1 8 6 8 4 4 6 1 8 4 8 6 7 6 8 8 5 7 4 7 3 2 5

Compound Soil drench 10 Kg/ha Dosage Foliar Spray Pre-emergence of of kg/ha Ex. No. Z R G O L M B S Z R G O L M B S Z R G O L M B S 10 5 3 6 4 2 1 2 11 5 7 4 9 7 7 7 8 8 2 4 2 5 1 7 4 9 6 7 6 7 6 5 12 5 7 8 4 2 3 4 4 1 4 2 2 2 3 13 5 2 4 1 2 14 5 4 5 9 6 4 6 7 6 1 3 2 8 5 5 4 15 8 6 4 2 5 5 2 9 6 4 7 9 7 6 4 6 2 1 2 7 5 2 7 2 2 16 5 1 4 4 4 1 1 4 2 4 1 17 5 4 7 4 3 2 1 2 1 2 5 18 8 1 7 2 5 7 3 9 6 7 7 7 8 2 7 2 2 1 1 3 1 8 5 3 4 6 7 2 2 1 19 5 7 5 3 5 6 4 1 4 4 2 5 2 20 7 7 7 7 3 3 4 5 5 5 5 9 6 6 7 9 8 7 6 8 4 7 3 1 3 2 7 3 1 3 7 6 3 2

Compound Soil drench 10 Kg/ha Dosage Foliar Spray Pre-emergence of of kg/ha Ex. No. Z R G O L M B S Z R G O L M B S Z R G O L M B S 21 5 2 6 4 7 4 3 1 2 2 1 2 1 22 5 6 8 4 7 2 1 5 7 2 2 23 5 5 9 5 2 6 7 4 1 3 7 4 4 5 2 24 2 5 5 2 3 5 4 1 2 25 4 7 2 3 4 3 5 6 1 8 7 2 6 9 8 7 1 4 7 4 8 6 2 26 5 4 3 3 1 1 1 3 27 5 6 5 6 1 4 4 5 28 5 4 1 4 1 2 4 4 6 1 4 1 1 5 29 5 6 7 4 2 7 4 6 1 2 3 2 2 3 4 30 5 5 2 4 3 4 3 4 2 2 2 1 4 1 2 3 1 1 31 5 5 3 4 3 5 6 1 3 2 2 2 3 4

Compound Soil drench 10 Kg/ha Dosage Foliar Spray Pre-emergence of of kg/ha Ex. No. Z R G O L M B S Z R G O L M B S Z R G O L M B S 32 5 3 5 3 2 3 4 4 1 3 4 2 1 33 5 3 5 3 4 1 2 2 2 2 34 2 4 5 5 3 9 4 2 5 6 5 4 6 4 5 1 2 7 2 2 2 2 2 2 35 6 5 6 5 7 5 6 7 6 6 6 2 1 3 6 4 1 6 4 5 6 5 5 5 2 5 36 5 1 1 6 1 2 37 5 6 7 2 1 3 7 38 5 5 6 4 5 6 4 5 1 4 2 2 2 2 2 39 5 4 7 4 3 6 5 1 2 2 2 2 2 40 5 5 3 9 6 4 6 6 7 5 4 4 1 4 4 2 2 5 4 2 41 5 7 2 1 2 1 2 1 42 6 2 5 5 2 7 2 1 3 3 7 1 4 2 6 1 6

Compound Soil drench 10 Kg/ha Dosage Foliar Spray Pre-emergence of of kg/ha Ex. No. Z R G O L M B S Z R G O L M B S Z R G O L M B S 43 5 7 1 2 44 5 2 7 8 4 1 2 2 2 45 5 6 5 1 2 3 46 5 4 2 2 1 2 47 6 7 6 7 2 5 7 7 8 8 4 8 8 6 8 1 7 6 8 7 2 8 7 6 7 48 5 4 6 2 2 6 7 7 7 6 4 7 1 3 5 5 6 6 6 5 2 7 49 5 4 3 7 7 1 2 2 6 5 50 3 4 3 3 2 4 7 2 5 4 2 2 2 3 4 7 6 2 4 4 1 3 2 2 2 3 4 6 5 4 2 51 1 1 2 6 2 5 2 2 2 7 2 1 2 2 1 6 52 8 7 8 6 2 8 8 7 5 7 7 7 2 2 7 7 7 7 8 8 5 2 1 6 6 7 5 7 6 6 8 8 2 53 6 4 7 6 2 3 2 5 4 2 7 2 4 7 2 5 6 7 2 1 1 7 4 6 1 2 3 6

Compound Soil drench 10 Kg/ha Dosage Foliar Spray Pre-emergence of of kg/ha Ex. No. Z R G O L M B S Z R G O L M B S Z R G O L M B S 54 5 9 2 9 9 6 4 3 1 2 2 3 2 2 55 2 5 6 2 2 7 5 3 6 2 6 7 2 1 2 3 6 56 5 2 7 1 3 5 1 2 6 3 5 57 6 7 7 6 7 6 4 5 4 5 8 2 6 7 5 7 8 8 5 2 8 7 4 1 2 4 8 6 7 5 6 7 7 5 5 2 58 5 2 2 1 1 2 1 7 1 1 5 59 2 4 5 2 3 2 2 3 8 8 2 4 1 2 2 2 3 6 60 5 2 7 2 4 7 8 3 1 2 6 4 1 61 5 4 6 2 4 2 3 2 5 1 62 5 6 6 4 5 2 4 2 4 6 4 1 * * * * * * * * * * * * * * * * 63 5 1 1 4 7 1 1 2 3 64 4 4 6 5 5 5 2 5 7 2 2 7 3 4 4 6 1 2 4 2 1 6 5 2 2 5 2

Compound Soil drench 10 Kg/ha Dosage Foliar Spray Pre-emergence of of kg/ha Ex. No. Z R G O L M B S Z R G O L M B S Z R G O L M B S 65 5 2 4 6 2 1 2 2 66 5 6 4 2 6 4 4 1 6 2 1 4 6 2 1 6 2 5 2 2 5 2 5 67 5 4 3 6 5 1 2 2 3 68 5 4 8 4 4 2 6 4 1 3 2 3 2 2

Claims

CLAIMS 1. A method of combating undesired plant growth at a locus, comprising applying to the locus a compound of general formula

where Rl represents an optionally substituted aryl or heteroaryl group; R2 represents an optionally substituted alkyl, alkoxy or aryl group; and R3 represents an optionally substituted alkyl, aryl, amino or amido group, or a group of general formula -CooR4 where R4 represents a hydrogen atom or an optionally substituted alkyl group; or R2 and R3 together represent an optionally substituted alkylene chain optionally interrupted in the chain by one or more hetero atoms; provided that Rl does not represent a phenyl group substituted by a nitro group at the 2-position and by an optionally substituted phenoxy group at the 4 position, when R2 represents an optionally substituted alkyl, alkoxy or phenyl group and R3 represents a group of general formula -COOR4.
2. A method as claimed in Claim 1, wherein R' represents a phenyl group, optionally substituted by halogen, cyano, nitro, oxyalkyleneoxy or optionally substituted alkyl, alkoxy, phenoxy or benzyloxy.
3. A method as claimed in Claim 1, wherein R' represents a phenyl group optionally substituted by one or two moieties independently selected from halogen, alkyl, alkoxy, benzyloxy, haloalkyl, cyano or nitro, or by a group -O-CH2-O-.
4. A method as claimed in any preceding claim, wherein R2 represents a phenyl, alkyl or alkoxy group.
5. A method as claimed in any preceding claim, wherein R3 represents a phenyl or amino group, an alkyl group, a monoalkylamido group, or a group of general formula -COOR41 where R4 represents a hydrogen atom or an alkyl group.
6. A method as claimed in any of Claims 1 to 3, wherein R2 and R3 together represent an optionally substituted alkylene chain.
7. A method as claimed in Claim 6, wherein R2 and R3 together represent -CH2-CtCH3)2-CH2- or - (CM2)3-.
8. Use of a compound of general formula I.as defined in any of Claims 1 to 7, as a herbicide.
9. A herbicidal composition comprising a compound of general formula I as defined in any of Claims 1 to 7, in association with at least one carrier.
10. A composition as claimed in Claim 9, having at least two carriers, at least one of which is a surface active agent.
11. A compound of general formula I, as defined in any of Claims 1 to 7, wherein Rl represents a phenyl group which is substituted by halogen, cyano.

oxyalkyleneoxy or optionally substituted alkyl, alkoxy, phenoxy or benzyloxy, or is a 2-thienyl group, and R2 and R3 together represent an optionally substituted alkylene chain; but not including 3-(4 fluorophenyl 6,7-dihydro-1,2-benzisoxazole-4(5H)-one.
12. A process for the preppration of a compound of general formula I, as defined by Claim 11, which comprises reacting a compound of general formula II with a compound of general formula III

when Hal represents a halogen atom and R', R2 and R3 are as defined in Claim 11.
13. A compound of general formula I, as defined by Claim 11, when prepared by a process as claimed in Claim 12.
14. A method, use, herbicidal composition, novel compound or process for making a novel compound, in accordance with the present invention substantially as hereinbefore described with particular reference to the Examples.