GB2194788A - Pyridinyl-substituted pyrrole dicarboxylate herbicides - Google Patents

Abstract

Compounds of the formula I: <IMAGE> [wherein R and R<1> are independently alkenyl, alkynyl or optionally halogenated alkyl; X, X<1> and X<2> are independently hydrogen, halogen, alkyl, hydroxy, alkoxy, mono- or dialkoxyalkyl, difluoromethoxy, alkylthio, amino, mono or dialkylamino; cyano or nitro; and R<2> is hydrogen, hydroxymethyl, -B(alkyl)2, -C(O)-R<3>, -CH2-O-C(O)-R<3>, -S-C(O)O- alkyl or -S-C(O)O- Ph (wherein R<3> has the meaning defined in the specification)] are useful as herbicides.

Description

SPECIFICATION Pyridinyl-substituted pyrrole dicarboxylate herbicides This invention relates to certain new 2-methyl-5-(2-pyridinyl)-pyrrole-3,4-dicarboxylates, their use as herbicides and herbicidal compositions containing these compounds.

It has been found that useful phytotoxic properties are possessed by compounds of the formula:

wherein R and R' each independently is an alkyl, mono- or polyhaloalkyl, alkenyl or alkynyl group of up to four carbon atoms, X, Xl and X2 each independently is a hydrogen or halogen atom, or a difluoromethyoxy, cyano, nitro, hydroxy, amino, alkyl, alkoxy, mono- or dialkoxyalkyl, alkylthio, mono- or dialkylamino group, wherein each alkyl moiety is of one to four carbon atoms, and R2 is (a) a hydrogen atom; (b) a hydroxymethyl group; (c) a -B(alkyl)2 group of two to six carbon atoms; (d) a -C(O)R3 group of one to eight carbon atoms; wherein R3 is a hydrogen atom, or an alkyl, alkenyl, alkynyl, cycloalkyl, cyclalkylalkyl, alkoxy, aryl, aryloxy, heteroaryl, arylalkyl, heteroarylalkyl group which may be substituted by one or more halogen atoms or by an alkoxy, alkylthio, alkyl, alkoxycarbonyl, carboxyl, alkylsulfinyl or alkylsulfonyl group; (e) a -CH2-O-C(O)-R4 group wherein R4 is a moiety defined by R3; (f) a -S-C(O)O-R5 group, wherein R5 is an alkyl or phenyl group.

Because of their characteristics, a preferred sub group of the compounds of formula I is composed of those individual species wherein R and R' each is an alkyl group-particularly methyiX, X and X2 each is a hydrogen, or halogen atom, or an alkyl, alkoxy, alkylthio, difluoromethoxy, or mono- or dialkoxymethyl group, and R2 is hydrogen.

The preparation, isolation and testing of typical individual species of the compounds of formula I are described in the examples which follow. The compounds are further illustrated and exemplified by the following further individual species, all of which are specifically contemplated in this invention. In the interest of brevity, and clarity, and to avoid repetition of sometimes long chemical names, these species will be identified in terms of formula I and the symbols used therein. In all cases, the moieties R and R1 each is methyl and R2 is hydrogen, with the other moieties being those shown.

Species x X xl x2 A methyl methyl hydrogen B ethyl hydrogen hydrogen C hydroxy hydrogen hydrogen D isopropoxy hydrogen hydrogen E hydroxymethyl hydrogen hydrogen F cyano hydrogen hydrogen G hydrogen cyano hydrogen H dimethylamino hydrogen hydrogen I methyl cyano hydrogen J trifluoromethyl hydrogen chlorine K chlorine hydrogen methoxy L methyl nitro hydrogen M methyl hydrogen methyl Further illustrative examples of the compounds of formula I wherein R2 is other than hydrogen are as follows, in all cases R and R1 each being methyl, and X, X and X2 each being hydrogen:: Species ~ R2 N acetyl O acetoxymethyl P cyclopropylcarbonyloxymethyl Q phenylcarbonyloxymethyl R l,l-dimethylethylcarbonyloxymethyl S 2-carboxyethylcarbonyloxymethyl T 2-carboxy-4-cyclohexen-1-ylcarbonyloxymethyl U 2-carboxy-2-pyridinyIcarbonyloxymethyl V methylthiomethylcarbonyloxymethyl W methylsulfinylmethylcarbonyloxymethyl X methylsulfonylmethylcarbonyloxymethyl Y 3-pyridinylcarbonyloxymethyl Z hydroxymethyl AA cyclopropylcarbonyl AB (l-tnethylpropyl)oxycarbonylthio Compounds of formula I can be prepared by treating a diketone of the formula

wherein Py represents the pyridinyl moiety as defined in formula I, with ammonium acetate.The cyclization is effected by (a) heating a mixture of the diketone, ammonium acetate and a substantial amount of acetic acid, as solvent, or (b) by heating a mixture of the diketone, ammonium acetate, a lower alkanol as solvent and a catalytic amount of acetic acid.

Diketones of formula II can be prepared by treating an R-ester of the 3-(2-pyridinyl)-3-oxopropanoic acid, this beta-ketoester having the formula

with an R1-ester of acetoacetic acid of the formula

under basic conditions in the presence of iodine. Treatment of the ketoester Ill with the ester IV is carried out by treating the ester Ill with a base such as sodium hydride in a solvent such as ether, treating the ester IV similarly, then slowly mixing the resulting solutions and heating the mixture. The resulting mixture is treated with a solution of iodine in ether, and that mixture is warmed to complete the reaction.

Alternatively, the ketoester Ill is converted to a carbanion, which is treated with an R1 ester of 2-chloroacetoacetic acid of the formula

to give a diketone of formula II. The carbanion is formed by treating the ketoester Ill with an alkali metal alkoxide, supported upon neutral alumina to form the carbanion of the formula

Preparation of the alkoxide/alumina reagent and treatment of the ketoester Ill with that reagent follow methodology described by G. Bram, et al., Synthetic Communications, 1980, Volume 10, pages 279-289, and J. A. M. van den Goorbergh and A. van der Gen, Recueil Trav. Chim.

Pays-Bas, 1984, volume 103, pages 90-96: the alkoxide/alumina reagent is prepared by stirring together a solution of the alkoxide in equal parts of the corresponding alcohol and tetrahydrofu ran (THF) and a powdered activated neutral alumina, and removing the solvents. Stirring together a solution of the ketoester lil in THF and the alkoxide/alumina reagent forms the carbanion.

The carbanion VI then is treated with the ester of 2-chloroacetoacetic acid V by mixing the two at about room temperature to give the diketone II.

Beta-ketoesters of formula III can be prepared by three variations of the Claisen Condensation, to wit: (1) treating a hot stirred mixture of an alkali metal alkoxide and benzene with a mixture of an R2-ester of picolinic acid, Py-C(O)O-R2, wherein R2 is lower alkyl, and an R-ester of acetic acid; (2) adding a methyl pyridinyl ketone,

to a hot mixture of a di-R-carbonate, sodium hydride and benzene; (3) heating a mixture of an alkyl ester of picolinic acid (defined in 1, above) an R ester of acetic acid and a base, such as sodium hydride.

Compounds of formula I also can be prepared according to the following sequence of reactions: (1) a beta-ketoester Ill is treated with an R1 ester of 2-chloro-3-((tosyl)hydrazono)butanoic acid of the formula

in the presence of an alkali metal alkoxide, to form an R,R1-diester of 2-((1-tosylhydrazono)ethyl) 3-((2-pyridinyl)carbonyl)- 1 ,4-butanedioic acid,

The treatment can be conducted by treating a solution of the ketoester Ill in a solvent such as THF with a solution of the alkoxide in the corresponding alcohol, then adding a solution of the ester VII in the same solvent.

(2) A solution of the diester VIII in methanol is treated with hydrogen chloride gas to form the R,Rl-diester of 2-methyl-1-((tosyl)amino)-5-(2-pyridinyl)pyrrole-3,4-dicarboxylic acid,

which is then dissolved in methanol and hydrogenated in the presence of Raney nickel to give the compound of formula I.

The ester VII can be prepared by treating a solution of tosyl hydrazine in a solvent such as THF with a solution of the R'-ester of 2-chloroacetoacetic acid in the same solvent according to the procedure of T. L. Gilchrist, et. al., Journal of the Chemical Society, Perkin Transactions pages 1803-7 (1983).

N-derivatives (R1 is other than hydrogen) can be prepared from the R1=hydrogen precursor by conventional techniques, as is illustrated and exemplified in Example 22, hereinafter.

Compounds of formula I have been found to adversely affect the growth of some plants, many of which are commonly considered as weeds, and therefore to be useful for controlling the growth of such unwanted plants. Compounds of formula I have been found to have selectivity with respect to some crop plants such as corn, soybeans and cotton-i.e., they control weeds at dosages at which they do not significantly harm the crop plants-particularly when applied pre-emergence or preplant incorporated (applied to and/or mixed with the soil before the seeds have sprouted.) Accordingly, the invention includes a method of combatting unwanted plants which comprises applying to the locus an effective amount of a compound of formula I.In the cases where it is desired to control weeds in crop plantings, it is of course preferable to employ the lowest dosage that will control the weeds, for this will minimize any possible deleterious effect of the compound upon the crop plants.

For application, a compound of formula I ordinarily is applied most effectively by formulating it with a suitable inert carrier or surface-active agent, or both. The invention, therefore also includes compositions suitable for combatting unwanted plants, such compositions comprising an inert carrier or surface-active agent, or both, and as active ingredient at least one compound of formula I.

The term "carrier" as used herein means an inert solid or liquid material, which may be inorganic or organic and of synthetic or natural origin, with which the active compound is mixed or formulated to facilitate its application to the plant, seed, soil or other object to be treated, or its storage, transport and/or handling. Any of the materials customarily employed in formulating pesticides, herbicides, or fungicides-i.e., horticulturally acceptable carriers-are suitable.

Suitable solid carriers are natural and synthetic clays and silicates, for example, natural silicas such as diatomaceous earths; magnesium silicates, for example, talcs; magnesium aluminum silicates, for example, attapulgites and vermiculites; aluminum silicates, for example, kaolinites, montmorillonites and micas; calcium carbonate; calcium sulfate; synthetic hydrated silicon oxides and synthetic calcium or aluminum silicates; elements such as, for example, carbon and sulfur; natural and synthetic resins such as, for example, coumarone resins, polyvinyl chloride and styrene polymers and copolymers; bitumen; waxes such as, for example, beeswax, paraffin wax, and chlorinated mineral waxes; solid fertilizers, for example, superphosphates; and ground, naturally-occurring, fibrous materials, such as ground corncobs.

Examples of suitable liquid carriers are water, alcohols such as isopropyl alcohol and glycols; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; ethers such as cellosolves (RTM); aromatic hydrocarbons such as benzene, toluene and xylene; petroleum fractions such as kerosene, light mineral oils; chlorinated hydrocarbons such as carbon tetrachloride, perchloroethylene and trichloromethane. Also suitable are liquefied, normally vaporous and gaseous compounds. Mixtures of different liquids are often suitable.

The surface-active agent may be an emulsifying agent or a dispersing agent or a wetting agent; it may be nonionic or ionic. Any of the surface-active agents usually applied in formulating herbicides or insecticides may be used. Examples of suitable surface-active agents are the sodium and calcium salts of polyacrylic acids and lignin sulfonic 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 alcohols or alkyl phenols, for example, p-octylphenol or p-octylcresol, with ethylene oxide and/or propylene oxide; sulfates or sulfonates of these condensation products, alkali or alkaline earth metal salts, preferably sodium salts, of sulfuric or sulfonic acid esters containing at least 10 carbon atoms in the molecule, for example, sodium lauryl sulfate, sodium secondary alkyl sulfates, sodium salts of sulfonated castor oil, and sodium alkylaryl sulfonates such as sodium dodecylbenzene sulfonate; and polymers of ethylene oxide and copolymers of ethylene oxide and propylene oxides.

The compositions of the invention may be prepared as wettable powders, dusts, granules, solutions, emulsifiable concentrates, emulsions, suspension concentrates and aerosols. Wettable powders are usually compounded to contain 25 to 75% by weight of active compound and usually contain, in addition to the solid carrier, 3-10% by weight of a dispersing agent, 2-15% of a surface-active agent and, where necessary, 0-10% by weight of stabilizer(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 or surfaceactive agent, and are diluted in the field with further solid carrier to give a composition usually containing 0.5-10% by weight of the active compound.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 0.5-25% by weight of the active compound, 0-1% by weight of additives such as stabilizers, slow release modifiers and binding agents. Emulsifiable concentrates usually contain, in addition to the solvent and, when necessary, cosolvent, 10-50% weight per volume of the active compound, 2-20% weight per volume emulsifiers and 0-20% weight per volume of appropriate additives such as stabilizers, penetrants and corrosion inhibitors.Suspension concentrates are compounded so as to obtain a stable, non-sedimenting, flowable product and usually contain 10-75% weight of the active compound, 0.5-5% weight of dispersing agents, 1-5% of surface-active agent, 0.1-10% weight of suspending agents, such as defoamers, corrosion inhibitors, stabilizers, penetrants and stickers, and as carrier, water or an organic liquid in which the active compound is substantially insoluble; certain organic solids or inorganic salts may be dissolved in the carrier to assist in preventing sedimentation or as antifreeze agents for water.

Of particular interest in current practice are water-dispersible granular formulations. These are in the form of dry, hard granules that are essentially dust-free, and are resistant to attrition on handling,-thus minimizing the formation of dust. On contact with water, the granules readily disintegrate to form stable suspensions of the particles of active material. Such formulations contain 90% or (up to 95%) more by weight of finely divided active material, 3-7% by weight of a blend of surfactants, which act as wetting, dispersing, suspending and binding agents, and may contain up to 3% by weight of a finely divided carrier, which acts as a resuspending agent.

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 present invention. The said emulsions may be of the water-in-oil or of the oil-in-water type, and may have thick, mayonnaise-like consistency.

It is evident from the foregoing that this invention contemplates compositions containing as little as about 0.5% by weight to as much as about 95% by weight of a compound of formula I as the active ingredient.

The compositions of the invention may also contain other ingredients, for example, other compounds possessing pesticidal, especially insecticidal, acaricidal, herbicidal or fungicidal properties, as are appropriate to the intended purpose.

Protection of a locus or area from undesirable plants is effected by applying a compound of formula I, ordinarily in a composition of one of the aforementioned types, to soil in which the seeds of the unwanted plants are present, or to the foliage- of the unwanted plants. The active compound, of course, is applied in an amount sufficient to exert the desired action.

The amount of the compound of the invention to be used in combatting undesired plants will naturally depend on the condition of the plants, the degree of activity desired, the formulation used, the mode of application, the climate, the season of the year, and other variables. Recommendations as to precise amounts are, therefore, not possible. In general, however, application to the locus to be protected of from 0.1 to 10.0 kg per hectare of the compound of formula I will be satisfactory.

The following examples describe the preparation, isolation and physical properties of typical individual species of the compounds of Formula I, in particular instances. In each case, the identity of each product, and each of any intermediate involved, was confirmed by appropriate chemical and spectral analyses.

Example 1 Diethyl 2-methyl-5-(2-pyridinyl)pyrrole-3,4-dicarboxylate (1) 5;75 g of sodium was treated with 100 ml of ethanol, the unreacted ethanol was stripped and the solid sodium ethoxide was dried by azeotroping with benzene. The sodium ethoxide was mixed with 150 ml of benzene, the mixture was stirred and heated to reflux and a mixture of 25 g of ethyl picolinate and 32.3 ml of ethyl acetate was added dropwise over 1 5 minutes. Then the mixture was stirred for 30 minutes and cooled. After 150 ml of water was added, glacial acetic acid was added until the mixture was acidic. The two liquid phases were separated. The organic phase was dried (Na2SO4), stripped of solvent and distilled in a Kugelrohr apparatus to give ethyl 3-(2-pyridinyl)-3-oxopropanoate (1 A), as a light yellow oil, b.p.: 95-110 /0.05 Torr.

1A also was prepared as follows: 73 ml of diethyl carbonate was added to a mixture of 30 g of hexane-washed sodium hydride and 150 ml of benzene, and the resulting mixture was heated at reflux temperature for 30 minutes, when 33 ml of 2-acetylpyridine was added dropwise over 60 minutes. The mixture was cooled to room temperature, 75 ml of glacial acetic acid and 250 ml of water were added, and the mixture was extracted with diethyl ether. The extract was dried, stripped of solvent and the residue was distilled in a Kugelrohr apparatus to give lA.

54 g of sodium methoxide was dissolved in a mixture of 100 ml of methanol and 100 ml of tetrahydrofuran (THF). 50 grams of aluminum oxide (activated, neutral, Brockmann I, Aldrich) was added and the mixture was stirred for 30 minutes. The solvents were removed under reduced pressure to give aluminum oxide-supported sodium ethoxide (it).

A solution of 9.7 g of 7A was dissolved in 15 ml of THF and added to 5.5 g of 1B. The mixture was stirred at room temperature for 30 minutes, then the solvent was evaporated under reduced pressure. 13.86 g of ethyl 2-chloroacetoacetate was added to the residue, the mixture was stirred for 90 hours at room temperature, then mixed with 200 ml of methylene chloride.

The resulting mixture was filtered, the filtrate was stripped of solvent in a Kugelrohr apparatus at 80-85"C/0.05 Torr. The residue was dissolved in 50 ml of acetic acid, 12.0 g of ammonium acetate was added and the mixture was heated at 100"C for 2 hours. After cooling, 200 ml of water was added, the mixture was extracted with methylene chloride, the extract was stripped of solvent and the residue was concentrated in a Kugelrohr apparatus at 50 C/0.05 Torr to remove acetic acid. The residue was dissolved in 100 ml of methylene chloride, 20 g of silica gel was added to the solution, the solvent was evaporated, and the residue was flash-chromatographed on silica gel, using a 3:2 v:v mixture of hexane and ethyl acetate as eluent.Work-up of the later fractions gave 1, as a light yellow solid, m.p.: 96-100"C.

Example 2 Dimethyl 2-methyl-5-(2-pyridinyl)pyrrole-3,4-dicarboxylate (2) Method A 51 ml of dimethyl carbonate was added to a mixture of 30 g of pentane-washed sodium hydride in 150 ml of benzene and the mixture was stirred and heated at reflux for 30 minutes.

Then a solution of 36 g of 2-acetylpyridine in 50 ml of benzene was added dropwise over 1 hour. 150 ml of THF was added to facilitate stirring, the mixture was stirred and heated for a further 1 hour, and cooled to room temperature. A mixture of 250 ml of water and 75 ml of glacial acetic acid was added dropwise while the mixture was cooled-to hold its temperature to about 15"C. Two liquid liquid layers formed; the upper layer was separated, dried (Na2SO4) and stripped of solvents. The residue was distilled in a Kugelrohr apparatus at 110-115"C/0.05 Torr., to give methyl 3-(2-pyridinyl)-3-oxopropanoate (2A), as a yellow oil.

2 was obtained, as a light yellow solid, by treating 2A according to the procedures described in Example 1 for preparing 1 from 1A.

Method B 2 also was obtained, as a white solid, as follows: A solution of 25 ml of methyl 2-chloroacetoacetate in 25 ml of THF was added dropwise over 30 minutes to a solution of 37.5 g of tosyl hydrazine in 150 ml of THF. The mixture was allowed to stand overnight, then heated at reflux for 2 hours, cooled to room temperature and stripped of solvent. The residue was then dissolved in 200 ml of ether. Crystallization occurred at room temperature. The collected solids were dried to give methyl 2-chloro-3-((tosyl)hydrazono)butanoate (2B), as a light yellow solid, m.p. 97-101"C.

0.46 g of sodium was treated with 30 ml of methanol, then a solution of 3.2 g of 2A in 30 ml of THF was added and the mixture was stirred for 15 minutes. 30 ml of THF was added, then a solution of 6.4 g of 2B in 30 ml of THF was added drop by drop and the mixture was stirred at room temperature for 1 hour. The solvents were evaporated, the residue was dissolved in 75 ml of water and the solution was extracted with methylene chloride. The extract was dried (Na2SO4) and stripped of solvent. The residue was dried, then flash-chromatographed on silica gel, using a 9:1 v:v mixture of methylene chloride and methanol as eluent, to give dimethyl 2-((1-tosylhydrazono)ethyl)-3-((2-pyridinyl)carbonyi)-1,4-butanedioate (2C), as a white solid, m.p.: 70-90"C.

For 5 minutes, hydrogen chloride gas was bubbled into a solution of 3.2 g of 2C in 50 ml of methanol, then the mixture was heated at reflux for 1 hour, cooled, and stripped of solvent. The residue was mixed with 100 ml of a 1:1 v:v mixture of water and methylene chloride and neutralized by shaking the mixture with solid sodium bicarbonate. The methylene chloride layer was separated, dried (Na2SO4) and stripped of solvent. The residue was dissolved in a minimum amount of methylene chloride, 100 ml of 1:1 v:v mixture of ether and pentane was added, and the mixture was allowed to stand overnight. The mixture was filtered, and the collected solids were dried, to give dimethyl 2-methyl- 1 -((tosyl)amino)-5-(2-pyridinyl)-pyrrole-3,4-dicarboxylate (2D), as a solid, m.p.: 145-147"C.

A solution of 0.443 g of 2D in 30 ml of methanol was added to a mixture of 1 g of Raney nickel in 20 ml of methanol. The mixture was heated at reflux for 3 hours, cooled and extracted with hot methanol. The extract was concentrated to about 5 ml, dissolved in water acidified to pH=2 with hydrochloric acid, and the solution was neutralized with solid sodium bicarbonate to pH=7. The mixture was extracted with methylene chloride, the extract was dried (Na2SO4), and stripped of solvent, and the residue was flash chromatographed on silica gel, using a 9:1 v:v mixture of methylene chloride and ethyl acetate as solvent. The later fractions gave 2.

Example 3 4-Ethyl 3-methyl 2-methyl-5-(2-pyridinyl)pyrrole-3,4-dicarboxylate (3) 1.25 g of pentane-washed sodium hydride was suspended in 50 ml of ether, then a solution of 10 g of 1A in 100 ml of ether was added dropwise over 20 minutes. The resulting mixture was stirred at room temperature for 20 minutes, giving mixture 3A.

A solution of 5.97 g of methyl acetoacetate. in 100 ml of ether was added dropwise over 20 minutes to a mixture of pentane-washed sodium hydride in 50 ml of ether, and the mixture was stirred at room temperature for 20 minutes. The resulting mixture was added to 3A, stirred at reflux for 30 minutes, and cooled to room temperature. 12.25 g of iodine in 200 ml of ether was added dropwise over 30 minutes to the stirred mixture and the mixture was stirred overnight at 35"C. The mixture was cooled to room temperature and 200 ml of water was added. The ether layer was separated, dried and stripped of solvent, the residue being 3B. The aqueous phase was neutralized with 1 N hydrochloric acid and extracted with methylene chloride. The extract was dried (Na2SO4) and stripped of solvent.The residue was mixed with ether and the mixture was filtered. The filtrate was stripped of solvent and the residue was combined with 3B to give 3C.

12.5 g of 3C, 15 g of ammonium acetate and 100 ml of glacial acetic acid were mixed and the mixture was heated at reflux for 2 hours. Then 200 ml of water was added and the resulting mixture was extracted with methylene chloride. The extract was stripped of solvent and the residue was flash-chromatographed on silica gel, using a 7:3 v:v mixture of hexane and ethyl acetate as eluent. The second fraction that was obtained gave 3, as a white solid, m.p.: 96-97"C.

Example 4 3-Ethyl 4-methyl 2-methyl-5-(2-pyridinyl)pyrrole-3,4-dicarboxylate (4) 4 was prepared, as a light yellow solid, m.p.: 75-80"C (with decomposition), by treating 2A by the procedures described in Example 3 for preparing 3 from lA.

Example 5 Dimethyl 2-methyl-5-(3-chloro-2-pyridinyl)pyrrole-3,4-dicarboxylate (5) At room temperature, 258.9 g of (85%) m-chloroperoxybenzoic acid was added in portions over 20 minutes to a stirred solution of 150 g of 3-chloropyridine in one liter of methylene chloride, the mixture being cooled to hold its temperature below 35"C. Then the mixture was stirred at room temperature for 2 days, washed with a 25% aqueous solution of potassium carbonate, dried (MgSO4) and stripped of volatiles. The product was triturated with ether at --78"C then stripped of solvent to give the N-oxide (5A), as a white solid, m.p.: 51.5-55"C.

125 g of trimethylsilyl cyanide was added to a stirred mixture of 54.3 g of 5A, 85 g of triethylamine and 420 ml of acetonitrile at room temperature. The mixture was heated at reflux for 4 hours, cooled and stripped of volatiles under reduced pressure. 3N aqueous sodium carbonate solution was added until the mixture was basic then the mixture was extracted with methylene chloride. The extract was dried (MgSO4), and stripped of solvent. The residue was chromatographed on silica gel, using a 1:3 v:v mixture of ethyl acetate and hexane as eluent, to give 3-chloro-2-cyanopyridine (5B), as an off-white solid, m.p.: 80.5-83"C.

64.1 g of 5B was refluxed in 460 ml of 2N aqueous sodium hydroxide solution for 1 hour.

The mixture was cooled, acidified to pH=2.5 with conentrated hydrochloric acid, stripped of water under reduced pressure, then by azeotroping with methanol. The residue was stirred with 250 ml of a 1:1 v:v mixture of methylene chloride and methanol, and the resulting mixture was filtered. The filtrate was stripped of volatiles (water bath temperature 60"C). This purification procedure was repeated, to give 3-chloropicolinic acid (5C), as a yellow solid, m.p.: 125.5-127.5"C.

6.3 ml of concentrated hydrochloric acid was added to a solution of 20 g of 5C in 400 ml of methanol and the mixture was heated at reflux for 6 hours. The mixture was cooled and stripped of methanol. The residue was treated with an aqueous sodium bicarbonate solution and extracted with methylene chloride. The extract was washed with saturated sodium chloride solutibn, dried (MgSO4) and stripped to give the methyl ester (5D) of 5C, as a brown oil.

66 g of 5D and 84.5 g of methyl acetate were added to 22.2 g of hexane-washed sodium hydride. Some reaction occurred immediately and after 5 minutes the mixture reacted vigorously.

When the reaction subsided, the mixture was quenched in one liter of ice water in a nitrogen atmosphere, acidified with acetic acid and filtered. The filtrate was extracted with methylene chloride, and the extract was dried (MgSO4), filtered and stripped of solvent. The residue was chromatographed on silica gel, using methylene chloride as eluent, to give methyl 3-(3-chloro-2 pyridinyl)-3-oxopropanoat-e (5E), as a pale yellow oil.

5 was prepared, as a white solid, m.p.: 113-115.5"C, by treating 5E according to the procedures described in Example 2 for preparing 2 from 2A by Method B.

Examples 6-15 The following individual species of formula I, wherein R and R' each was methyl, and each of X, X' and X2 not mentioned was hydrogen, were prepared by the procedures described in the stated Example.

Procedure of Physical Properties, Species X, X1, x2 Example melting point, C 6 X2 = ethyl 1 Light orange solid, 115-116.5 7 X2 = Cl 1 Yellow solid, 119.5-121.5 8 X = (F2HCO-) 1 Yellow solid, 131-133 9 X = methyl 1 White solid, 87.5-91 (with decomposition) 10 x2 = I 1 Orange semisolid, 53-114 11 X = I 1 Off-white solid, 139-147 12 X1 = Cl 1 Light yellow solid, 124.5-128 13 x1 = methoxy 1 Yellow solid, 135-138 14 X,P F 2B Light green solid, 120.5-125.5 15 X = Cl, x2 = Cl 2B Off-white solid, 180-182.5 C 16 X - methoxy, 2B Off-white solid, X2 = Cl 168-169.5*C 17 X - methoxy 2B Off-white solid, 150-152.5 C 18 X1 = methyl 2B White solid, 135.5-1390C 19 X1 = tert-butyl 2B White solid, 123.5-1240C 20 X2 =, dimethoxy- 1 Brown oil methyl Example 21 Dimethyl 2-methyl-5-(4-(methylthio)-2-(2-pyridinyl)pyrrole-3,4-dicarboxylate (21) 0.10 g of sodium mercaptan was added to a solution of 0.17 g of 12 in 5 ml of dimethylfor mamide at room temperature. The mixture was stirred at 80"C overnight, cooled and poured into 10 ml of water. The mixture was acidified with glacial acetic acid and extracted with methylene chloride. The extract was dried (Na2SO4) and stripped of solvent.The residue was flash chroma tographed on silica gel, using a 5:95 v:v mixture of ethyl acetate and methylene chloride as eluent. The later fractions were stripped of eluent, the residue was recrystallized from ether at -78"C, and the product was dried under reduced pressure to give 21, as an off-white solid, m.p. : 140-142.5 C.

Example 22 Dimethyl 1 -(methoxymethylcarbonyloxymethyl)-2-methyl-5-(2-pyridinyl)pyrrole-3 4-di- carboxylate (22) A solution of 22.9 g of N,N'-dicyciohexyicarbodiimide in 150 ml of anhydrous ether was added to a stirred solution of 2-methoxyacetic acid at room temperature. The temperature of the mixture rose to 31 C. After 2 hours of stirring, the mixture was filtered and the filtrate was stripped of solvent. The residue was cooled to 0 C and filtered, to give the anhydride of 2 methoxyacetic acid (22A), as a yellow oil.

A mixture of 0.79 g of 2, 1.64 g of 22A and 0.17 g of paraformaldehyde was heated at 1200C for 2.5 hours. The mixture was cooled to room temperature and distilled in a Kugelrohr apparatus to remove anhydride and 2-methoxyacetic acid and the residue was chromatographed on silica gel, with a 1:4 v:v mixture of ether and methylene chloride as eluent. The later fractions gave 22, as light-green oil.

Example 23 Herbicidal Activity In the following examples, the species of plants that were tested were: Abbreviation Barnyardgrass (watergrass)-Echinocloa crus-galli BYGR Downy brome-Bromus tectorum DOBR Yellow foxtail-Setaria glauca YEFT Sicklepod-Cassia obtusifdlia SIPO Velvetleaf-Abutllon theophrasti VELE Garden cress-Lepidium sativum GACR Johnsongrass-Sorghum halepense JOGR Morningglory-lpomoea sp. MOGL Field bindweed-Convolvulus arvensis FIBW Nightshade-Solanum sp.NISH Blackgrass-Alopecurus myosuroides BLGR Yellow millet-Panicum miliceum YEMI Large crabgrass--Digitaria sanguinalis LAGG Redroot pigweed-Amaranthus retroflexus RRPW Hemp sesbania-Sesbania exaltata HESE Prickly sida-Sida spinosa PRSI Test Procedures The preemergence (soil) herbicidal activity of compounds of formula I was evaluated by planting seeds of downy brome, johnsongrass, yellow foxtail, barnyardgrass, yellow millet, blackgrass, hemp sesbania, velvetleaf, morningglory, prickly sida, sicklepod and garden cress in test tubes, nominally measuring 25 x 200 millimeters, filled about three-quarters full untreated soil, in each case covered on top with about 2.5 cubic centimeters of soil treated with 0.1 milligram of the test compound, to give a dosage of 2.0 pounds of test compound per acre. The seeds were planted on top of the treated soil and covered with about 1.5 cubic centimeters of untreated soil. The planted soil was held under a controlled regimen of temperature, moisture, and light.At 10 days, the amounts of germination and growth in each tube were evaluated on a O to 9 scale, the numeric ratings having the following meanings: Rating Meaning 9 No living tjssue 8 Plant severely damaged and expected to die 7 Plant badly damaged, but expected to live 6 Moderate damage, but complete recovery expected 5 Intermediate damage (probably unacceptable for crop plants) 3-4 Observable damage 1-2 Plant slightly affected, possibly by the chemical, possibly due to biological variability O No visible effect The postemergence (foliar) herbicidal activity of compounds of formula I was evaluated by spraying 9-day-old large crabgrass plants, 9-day-old pigweed plants, 6-day-old johnsongrass plants, 9-day-old velvetleaf plants, 8-day-old yellow foxtail plants, 9-day-old sicklepod plants, 5day-old morningglory plants, 5-day-old barnyardgrass plants, 6-day-old yellow millet plants, 9day-old nightshade plants, 9-day-old prickly sida plants and 7-day-oid field bindweed plants to runoff with 2.4 milliliters of a liquid formulation containing 0.5 milligram of the test compound (one pound of the test compound per acre). The sprayed plants were held under a controlled regimen of temperature, moisture and light for 7 to 8 days, when the effect of the test compound was evaluated visually, the results being rated on the 0 to 9 scale described above.

Results of the preemergence and postemergence herbicidal activity tests are set forth in Tables I and II.

table I. PREEMERGENCE HERBICIDAL ACTIVITY Compound No. DOBR JOGR YEFT BYGR YENI BLGR HESE VELE MOGL PRSI SIPO GAGR 1 0 -a) 0 - - - - 0 0 - - 2 5 3 5 8 8 3 5 8 9 8 8 8 3 8 - 6 - - - - 8 9 - - 4 0 2 0 0 0 0 2 2 7 0 0 5 5 9 7 8 9 5 5 9 8 9 9 9 8 6 2 2 2 2 0 0 4 4 4 - 2 7 7 0 0 2 3 0 2 5 3 5 3 3 5 8 7 3 0 7 0 3 9 7 9 3 8 9 9 6 7 8 9 8 7 9 9 9 8 9 9 10 0 0 0 2 0 3 2 3 3 2 0 6 11 3 2 3 6 0 0 8 8 8 3 9 8 12 0 3 0 8 0 4 7 5 8 3 3 9 13 0 0 0 0 0 0 0 0 4 0 0 4 14 7 6 7 8 8 4 9 8 9 8 9 8 15 9 3 4 9 7 5 9 8 7 9 7 8 16 5 4 2 6 5 4 8 6 8 3 4 7 17 2 2 2 0 2 3 8 7 8 0 6 7 18 0 0 0 0 0 0 0 5 5 0 0 0 20 0 0 0 0 0 0 0 0 0 0 0 0 21 0 0 0 0 0 0 0 0 0 0 0 0 22 4 6 6 8 7 4 8 8 9 8 7 9 a) - indicates that the compound was not tested with respect to this species.

table I. PREEMERGENCE HERBICIDAL ACTIVITY Compound No. lACC JOGR YEFT BYGR YEMI RRPW NISH VELE MOGL PRSI SIPO FIBW 1 -a) 5 5 - - - - 4 7 - - 2 3 3 3 9 6 8 9 7 9 7 9 7 3 - 5 4 - - - - 9 7 - - 4 0 5 3 3 7 4 6 0 6 4 5 3 5 3 5 9 3 4 5 7 9 8 5 9 9 6 3 4 9 6 6 8 9 9 9 5 9 9 7 7 6 9 7 5 5 9 6 9 7 9 9 8 2 2 2 2 5 5 8 5 8 3 7 5 9 0 0 7 0 3 3 5 7 6 6 7 5 10 6 7 7 5 5 8 9 7 9 5 9 9 11 3 6 6 3 4 7 6 6 7 3 9 9 12 7 9 9 9 8 9 9 9 9 7 9 9 13 3 9 9 6 8 7 8 4 7 5 7 8 14 7 4 9 2 7 7 9 9 8 4 8 8 15 7 6 7 6 7 8 9 6 9 5 9 9 16 0 4 7 9 4 3 0 0 8 0 5 5 17 0 5 3 0 2 0 0 3 7 0 4 5 18 7 7 6 8 5 6 8 5 8 4 8 9 20 4 3 4 4 3 4 9 4 9 4 5 9 21 4 6 7 3 7 5 9 5 9 3 9 9 22 0 5 3 5 7 5 7 3 8 3 7 5 a) - indicates that the compound was not tested with respect to this species.

Claims (4)

1. A compound of the formula:

wherein R and R' each independently is an alkyl, mono- or polyhaloalkyl, alkenyl or alkynyl group of up to four carbon atoms, X, Xl and X2 each independently is a hydrogen or halogen atom, or a difluoromethoxy, cyano, nitro, hydroxy, amino, alkyl, alkoxy, mono- or dialkoxyalkyl, alkylthio, mono- or dialkylamino group, wherein each alkyl moiety is of one to four carbon atoms, and R2 is (a) a hydrogen atom; (b) a hydroxymethyl group; (c) a -B(alkyl)2 group of two to six carbon atoms; (d) a -C(O)R3 group of one to eight carbon atoms; wherein R3 is a hydrogen atom, or an alkyl, alkenyl, alkynyl, cycloalkyl, cyclalkylalkyl, alkoxy, aryl, aryloxy, heteroaryl, arylalkyl, heteroarylalkyl group which may be substituted by one or more halogen atoms or by an alkoxy, alkylthio, alkyl, alkoxycarbonyl, carboxyl, alkylsulfinyl or alkylsulfonyl group; (e) a -CH2-O-C(O)-R4 group wherein R4 is a moiety defined by R3; (f) a -S-C(O)O-R5 group, wherein R5 is an alkyl or phenyl group.

2. A compound of formula I as defined in claim 1 substantially as described herein with reference to any one of Examples 1 to 22.

3. A phytotoxic composition comprising an effective amount of a compound of claim 1 together with a horticultural carrier and/or a surfactant.

4. A method for controlling unwanted plant growth at a locus that comprises applying to the locus an effective amount of a compound of claim 1 or 2 or a composition of claim 3.