WO1994022854A1

WO1994022854A1 - Herbicidal 1,4-di-heteroaryl pyrazolidin-3,5-diones

Info

Publication number: WO1994022854A1
Application number: PCT/EP1994/000967
Authority: WO
Inventors: Stefan Scheiblich
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 1993-03-26
Filing date: 1994-03-24
Publication date: 1994-10-13
Also published as: ZA942074B

Abstract

Herbicidally active, 1,4-di-substituted pyrazolidindiones of general formula (I), wherein A, B and D, which may be the same or different, each independently represents N or CR?6; R1, R2, R4, R5 and R6¿, which may be the same or different, each independently represents a hydrogen or halogen atom, a formyl, cyano, carboxy, or azido group, or an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl, alkoxy, alkenyloxy, alkynyloxy, alkylthio, alkenylthio, alkynylthio, aryloxy, alkylamino, alkylcarbonyl or alkoxycarbonyl group; and R3 represents a hydrogen atom or an optionally substituted alkyl, alkenyl, alkynyl, tetrahydrofurfuryl, cycloalkyl, aralkyl or phenyl group; together with compositions containing such compounds as active ingredient, and their herbicidal use.

Description

Herbicidal 1,4-di-heteroaryl pyrazolidin-3,5-diones

This invention relates to certain 1,4-di-heteroaryl

pyrazolidindiones having herbicidal activity, processes for their preparation, compositions containing such compounds and their use as herbicides to combat undesired plant growth.

Certain derivatives of pyrazolidin-3, 5-dione (and its tautomeric forms) are known to affect plant growth. Thus, European Patent Application 508126 describes 3-hydroxy-4-aryl-5-oxo- pyrazolidine derivatives having alkyl, alkenyl or aryl substituents at the 1-position; such compounds being active against ecto parasites and also certain plant species. Similar compounds having hydrogen or alkyl at the 4-position are also disclosed in European Patent Application 0265305 as intermediates in the preparation of herbicidally active 5-pyrazolones. PCT patent specification WO 92/16510 describes pyrazolidin-3, 5-diones substituted at the 4-position with a phenyl, pyridine or naphthalene group, and at the 1-(and/or 2-) position with an acyclic hydrocarbon group, those compounds being active against insects, mites and certain plant species.

It has now been found that particularly useful herbicidal activity is present in pyrazolidindiones bearing

nitrogen-containing heteroaryl substituents at both the 1- and the 4-positions.

Accordingly, the present invention provides 1,4-di-substituted pyrazolidindiones of generai formula I:-

wherein A, B and D, which may be the same or different, each independently represents N or CR⁶, R¹ , R², R⁴, R⁵ and R⁶, which may be the same or different, each

independently represents a hydrogen or halogen atom, a formyl, cyano, carboxy, or azido group, or an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl, alkoxy, alkenyloxy, alkynyloxy, alkylthio, alkenylthio,

alkynylthio, aryloxy, alkylamino, alkylcarbonyl or alkoxycarbonyl group; and R³ represents a hydrogen atom or an optionally substituted alkyl, alkenyl, alkynyl, tetrahydrofurfuryl, cycloalkyl, aralkyl or phenyl group; together with salts of such compounds and tautomers thereof.

An alkyl, alkenyl or alkynyl radical or moiety may be a straight or branched chain group. Generally an alkyl radical or moiety has from 1 to 12 carbon atoms, preferably from 1 to 6, especially from 1 to 4, carbon atoms. Alkenyl and alkynyl radicals or moieties

suitably have from 2 to 12 carbon atoms, preferably from 2 to 6, especially from 2 to 4, carbon atoms.

Cycloalkyl groups suitably have from 3 to 8 carbon atom ring members.

The aryl moiety in an aralkyl radical, may be a single or fused carbocyclic ring system having from 6 to 10 ring members. Suitably an aryl moiety comprises a single ring system and preferably is a phenyl ring.

Certain radicals represented by the symbols R¹, R², R³, R⁴, R⁵ and R⁶ may be unsubstituted or substituted. Where substituents are present, the substituent groups may be any of those customarily employed in the

modification and/or development of pesticidal compounds and are especially substituents that maintain or enhance the herbicidal activity associated with the compounds of the present invention, or influence persistence of action, soil or plant penetration, or any other desirable property of such herbicidal compounds. There may be one or more of the same or different substituents present in each radical.

Optional substituents for alkyl, alkenyl, alkynyl, cycloalkyl, alkoxy, alkenyloxy, alkynyloxy, alkylthio, alkenylthio, tetrahydrofurfuryl, alkynylthio, alkylamino, alkylcarbonyl or alkoxycarbonyl groups may be independently selected from one or more of halogen atoms and

alkoxy, alkenyloxy, hydroxy, alkylthio, alkylsulphonyl,

alkylsulphinyl, alkylenedioxy, alkylenedithio, haloalkyl and alkoxycarbonyl groups, and dialkyliminoxy, optionally substituted amino, trialkylsilyl, alkylcarbonyl, alkoxycarbonyl, carboxy, cyano, thiocyanato and optionally substituted aminocarbonyl groups.

Optional substituents for the aryl moiety in an aralkyl group may be independently selected from one or more of halogen atoms and nitro, cyano, alkyl, haloalkyl, alkoxy, alkylthio, aryloxy, alkoxycarbonyl and aralkoxycarbonyl groups.

A and D preferably represent CH, and B preferably represents a nitrogen atom.

Suitable examples of the groups R¹, R², R⁴ and R⁵ include alkyl and alkoxy groups of up to 6 carbon atoms, especially methyl and methoxy. Preferably R¹ is the same as R², and R⁴ the same as R 5. Suitable examples of group R³ include a hydrogen atom, alkyl and alkenyl groups of up to 6, especially 2, 3 or 4, carbon atoms, optionally substituted by a halogen atom or cyano group,

cyclopentyl, cyclohexyl, benzyl and phenyl.

The pyrazolidindiones may exist in a variety of tautomeric forms, all of which fall within the scope of this invention, together with salts thereof.

The present invention also includes processes for the preparation of compounds of formula I. One process, which can be used when B is N, A and D each has the same meaning, and R ¹ and R² have the same meanings as R⁴ and R⁵, comprises reacting a

1- substituted pyrazolidindione of formula II:

with a 2-substituted pyrimidine or triazine of formula III : -

wherein D, R ³ , R⁴ and R⁵ have the meanings as defined for formula I and X represents a leaving group.

A leaving group is any group that will, under the reaction conditions, cleave from the starting material thus promoting reaction at the site formerly occupied by that group. In the compounds of general formula III, the leaving group is suitably a halogen atom, for example a bromine, chlorine, fluorine or iodine atom, a sulphonate or quaternary ammonium group, or, more

conveniently, an alkanesulphonyl group such as methane- sulphonyl.

It is preferred that the reaction is carried out under basic conditions. The basic conditions may suitably be provided, for example, by an alkali metal hydroxide or hydride, such as sodium or potassium hydroxide or hydride, an alkaline earth metal hydride, such as calcium hydride, an alkali metal carbonate or bicarbonate, such as sodium or potassium carbonate or sodium bicarbonate, an alkali metal alkoxide, such as potassium t-butoxide, or a tertiary amine, such as triethylamine, pyridine or 1,8-diazabicyclo[5.4.0]- undec-7-ene.

The reaction is suitably carried out in an inert organic solvent such as a hydrocarbon solvent, e.g. benzene or toluene, a chlorinated hydrocarbon, e.g. dichloromethane or chloroform, an alcohol, e.g. methanol or ethanol, an ether, e.g. diethyl ether, tetrahydrofuran, 1,4-dioxane, a ketone, e.g. acetone or methyl ethyl ketone, an ester, e.g. ethyl acetate, an aprotic polar solvent, e.g. dimethylformamide, dimethylacetamide or

dimethylsulphoxide or a nitrile, e.g. acetonitrile, or in water, with appropriate selection of the agent generating the basic conditions for the reaction. The process of the invention may be carried out over a wide temperature range, for example from ambient (-20ºC) to the reflux temperature of the reaction medium.

The amounts of the reactants II and III may vary suitably within the range of 0.1 to 10 moles of II per mole of III. However substantially equimolar amounts of II and III are preferably employed.

The starting material of formula II may be prepared by reacting a N-substituted hydrazine of formula IV

H₂N-NHR³ (IV)

(prepared according to Stroh and Scharnow, Chem. Ber. 98 (1965) 1588, with diethyl malonate and sodium methoxide.

An alternative process, which can be used when A differs from

D and/or R¹/R² differ from R⁴/R⁵, comprises reacting a

2-pyrimidinyl hydrazine of formula (V):

with a substituted acetic acid derivative of formula VI :

This reaction is suitably carried out in the presence of dimethyl- aminopyridine and in solution in a solvent such as tetrahydrofuran, and is effected via reaction with carbonyldiimidazole and sodium hydride. The 2-pyrimidinyl hydrazine of formula V may be prepared by reacting the corresponding 2-hydrazinopyrimidine with an aldehyde of formula R³CHO, or analogous ketones, followed by hydrogenation, suitably with gaseous hydrogen over Raney nickel, or by reduction with sodium borohydride. When R³ is a tertiary alkyl group, a suitable preparation involves reacting a pyrimidine of formula VII with the tertiary alkyl hydrazine.

The substituted acetic acid derivative of formula VI may be prepared from a 2-substituted pyrimidine of formula III (or the analogous 2-substituted pyridine) by reaction with a malonic ester (eg dibenzyl) and sodium hydride, followed by hydrogenation, suitably with gaseous hydrogen in the presence of palladium.

A further alternative process comprises the reaction of a 2-pyrimidinyl hydrazine of formula V with methoxycarbonylacetyl halide (especially chloride), folLowed by reaction of the resulting malonylhydrazide with a 2-substituted compound of formula VII:

wherein R⁴ and R⁵ are as defined for formula I and X represents a leaving group as defined for formula III.

The prepared compounds of general formula I may, if desired, be isolated and purified using conventional techniques.

The starting pyrimidines of general formulae III, V and VII may be prepared by conventional techniques, for example those described in European Patent Specification 0019450. Certain of these pyrimidines, the compounds of formula VII, and other intermediates are novel compounds, and as such form a further aspect of this invention.

Compounds of the general formula I have been found to have interesting activity as herbicides having a wide range of pre- and post-emergence activity against undesirable species. The present invention therefore provides a herbicidal composition which comprises a compound of the present invention in association with a carrier.

The present invention additionally encompasses the preparation of such a herbicidal composition by the process of bringing a carrier into association with a compound of the present invention.

Preferably there are at least two carriers in a composition of the present invention, at least one of which is a surface-active agent.

The present invention further provides the use of a compound 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 composition or compound according to the

invention. The locus may, for example, be the soil or plants in a crop area. Application to the locus may be pre-emergence or post-emergence. The dosage of active ingredient used may, for example, be from 0.01 to 10kg/ha, preferably 0.01 to 4kg/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, which may for example be a plant, seed or soil, 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 herbicidal 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 cyclohexanone; ether; 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 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 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 herbicidal composition of the invention may also contain other biologically active ingredients , for example compounds possessing herbicidal , insecticidal or fungicidal properties .

The following Examples illustrate the invention. The structures of the compounds of the invention prepared in the following Examples were confirmed by mass spectrometry and NMR.

Example 1

1,4-bis(4,6-dimethoxypyrimidin-2-yl)-2-(2-chloroallyl)

pyrazolidindione

A) N-(2-chloroallyl)pyrazolidindione

(2-Chloroallyl)hydrazine (8.52g; prepared according to Stroh and Scharnow, Chem. Ber. 98 (1965) 1588) and diethyl malonate (12.8g) were added to a solution of sodium (7.36g) in methanol (120ml), and the mixture stirred for 3 days at room temperature. After aqueous work up, the solution was acidified,

chromatographically separated, and washed with ethylacetate (or diisopropyl ether) to yield the desired product as a solid, m.pt. 141-143°C.

B) The product A) (1.22g) and 4 ,6-dimethoxy- 2-methyl- sulphonyl pyrimidine (3.06g) were dissolved in dimethyl formamide (25ml) and sodium hydride (0.87g of 60% dispersion in mineral oil) was added at room temperature, portionwise with cooling. After stirring for 20 hours, the solution was poured into water and extracted with ethyl acetate. The aqueous phase was acidified, and the desired title product isolated by filtration (or extraction with ethyl acetate) to yield, after recrystallisation, a solid m.pt. 182-184ºC. Analysis: Calc. C 47.96; H 4.25; N 18.64%

Found: C 46.75; H 4.75; N 17.82% Example 2

1-(4,6-dimethyl pyrimidin-2-yl)-4-(4,6-dimethoxypyrimidin-2-yl),

2-isobutyl pyrazolidindione

A) Sodium hydride (2.88g; 60% dispersion in mineral oil) was washed with petroleum ether, and dispersed in tetrahydrofuran (50ml). To this were added, at room temperature dibenzylmalonate (in tetrahydrofuran, 25ml) and 4,6-dimethoxy-2-methylsulphonyl pyrimidine. The mixture was refluxed for 12 hours, the excess hydride destroyed by addition of acetic acid, and the solvent evaporated off. The residue was dissolved in ethyl acetate, washed with bicarbonate solution and chromatographically separated to yield pyrimidinyl malonic acid ester as a solid m.pt. 61-62ºC.

B) The pyrimidinyl malonic acid ester prepared in A) (8.3g) was taken up in ethanol (80ml) and hydrogenated (at 140kPa) with 10% palladium on charcoal (0.8g). The resulting mixture was chromatographically separated to yield the corresponding

pyrimidinyl acetic acid as a solid, m.pt. 115°C.

C) 4,6-dimethyl-2-hydrazinopyrimidine (13.8g) in water (350ml) and acetic acid (8ral) was reacted with 2-methylpropanal for 2 hours at room temperature. The pH was raised above 7 by the addition of ammonia and the product extracted with methylene dichloride and recrystallised from petroleum ether to yield the corresponding hydrazone, m.pt. 107-108ºC.

D) The hydrazone prepared in C) was hydrogenated according to the literature process of Dohmori et al, Chem. Pharm. Bull.

17(1969) 1479 to yield, after chromatographic purification, the corresponding isobutyl hydrazine, m.pt. 62-64°C.

E) The pyrimidinyl acetic acid prepared in B) (0.5g) in tetrahydrofuran (4ml) was reacted with carbonyl diimidazole (0.48g) and, after 2½. hours, with the isobutyl hydrazine prepared in D) (0.49g) and a catalytic amount of 4-dimethylamino pyridine. After stirring for a further 6 hours, the mixture was diluted with tetrahydrofuran (10ml) and treated with further carbonyldiimidazole

(0.45g) and sodium hydride (0.11g 60% dispersion in mineral oil) The mixture was heated to 50° C for several hours with TLC control and worked up as in Example 1 to yield the title product as a solid, m.pt. 207-208ºC (dec). Analysis: Calc. C 56.99; H 6.04; N 20.99%. Found C 56.45; H 7.71; N 21.22%. Alternatively, the reaction product of the pyrimidinyl acetic acid and

isobutylhydrazino pyrimidine may be isolated as an intermediate and thereafter cyclised as above.

Example 3 (S)

1-(4,6-dimethoxypyrimidin-2-yl),4-(4,6-dimethoxytriazin-2-yl), 2-tert-butylpyrazolidindione (sodium salt)

A) tert.butyl hydrazine hydrochloride (3.1g) and

4,6-dimethoxy-2-methylsulphonyl pyrimidine (5.45g) were added to a solution of sodium hydroxide (1.1g) in ethanol (50ml). The mixture was refluxed for 18 hours, sodium carbonate (1.5g) added and reflux continued for a further 20 hours. The mixture was poured into dilute sulphuric acid, extracted and the acidic solution made alkaline with sodium carbonate. Ether extraction yielded

1-tert.butyl-2-(4,6-dimethoxy-pyrimidin-2-yl) hydrazine as a solid m.pt. 96-100°C.

B) Methoxycarbonyl acetyl chloride (0.48g) was added .

dropwise at 0°C to a mixture of the pyrimidine butyl hydrazine prepared in A (0.68g), a catalytic amount of 4-dimethylamino pyridine and pyridine (0.26g) in methylene dichloride (25ml).

After stirring overnight at room temperature, the mixture was washed with water to yield the corresponding malonyl hydrazide, m.pt. 140-142°C.

C) A catalytic amount of 4-dimethylamino pyridine and

2-chloro-4,6-dimethoxy-1,3,5-triazine (0.48g) were added at 0°C to the malonyl hydrazide prepared in B (0.81g) dissolved in tetra- hydrofuran (15ml). Sodium hydride was added in portions (total 0.20g, 60% dispersion in mineral oil), and the mixture stirred overnight at room temperature. The mixture was poured into water and the sodium salt of the title product extracted with methylene dichloride, and recrystallised from isopropanol/disopropylether. M.Pt. 244°C (dec). Analysis: Calc: C47.47; H 4.87; N 21.53%.

Pound: C 47.58; H 5.44; N 20.23%. Example 4

Following a similar procedure to that described in Example 1, the corresponding 2-benzyl pyrazolidindione was prepared. This product (0.25g) was then hydrogenated in methanol (5ml) and dioxane (3ml) at 140kPa and 50ºC with 10% palladium on charcoal (20mg). The warm solution was filtered over silica gel, washed with methanol and the filtrates evaporated to yield

1,4-bis(4,6-dimethoxypyridimidin-2-yl) pyrazolidindione, m.pt.

201-203ºC. Nmr data (1H in DMSO-d6); 6.19 ppm(s.1H); 5.84(s,1H); 4.06(s,6H); 3.95(s,6H). Mol. wt. 376 by mass spect.

Examples 5-51

Following procedures analogous to those described in Examples 1-4, further compounds were prepared whose details are given below in Table I. In that Table, the structure of each compound is defined by reference to the substituents in formula (A) bellw:

Example 51

Herbicidal Activity

To evaluate their herbicidal activity, compounds 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 X-155. These acetone solutions were diluted with water and the resulting formulations applied at dosage levels corresponding to 5 kg or 1 kg 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 seale approximates to a 10% increase in the level of effect.

The results of the tests are set out in Table II below, in which the compounds are identified by reference to the preceding examples. Absence of a numeral in the Table indicates a zero rating, an asterisk indicates that no result was obtained.

Claims

C L A I M S

1. 1,4-di-substituted pyrazolidindiones of general formula I:-

wherein A, B and D, which may be the same or different, each independently represents N or CR⁶; R¹ , R², R⁴, R⁵ and R⁶, which may be the same or different, each independently represents a hydrogen or halogen atom, a formyl, cyano, carboxy, or azido group, or an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl, alkoxy, alkenyloxy, alkynyloxy, alkylthio, alkenylthio, alkynylthio, aryloxy, alkylamino, alkylcarbonyl or alkoxycarbonyl group; and R³ represents a hydrogen atom or an optionally substituted alkyl, alkenyl, alkynyl, tetrahydrofurfuryl, cycloalkyl, aralkyl or phenyl group; together with salts of such compounds and tautomers thereof.

2. Compounds as claimed in claim 1 wherein A represents CH; B represents a nitrogen atom; D represents CH or a nitrogen atom; R¹, R², R⁴ and R⁵ each independently represents an alkyl or alkoxy group of up to 6.carbon atoms; and R³ represents a hydrogen atom or an alkyl, alkenyl or cycloalkyl group of up to 6 carbon atoms, optionally substituted by a halogen atom or a cyano group.

3. Compounds as claimed in claim 1 or 2 wherein R ¹ and R² each has the same meaning and both represent a methyl or methoxy group.

4. Compounds as claimed in claim 1, 2 or 3 wherein R ⁴ and R⁵ each has the same meaning and both represent a methyl or methoxy group.

5. Compounds as claimed in any one of claims 1-4, wherein D represents CH and R³ represents an alkyl or alkenyl group containing 2 , 3 or 4 carbon atoms , optionally substituted by a chlorine atom.

6. Compounds as claimed in claim 1 , which is described in any of Example 1-20.

7. Process for the preparation of a compound as claimed in claim 1 , which comprises reacting a 1-substituted pyrazolidindione of formula II : -

with a 2-substituted pyrimidine or triazine of formula III

wherein D, R³, R⁴ and R⁵ have the meanings defined for formula I and X represents a leaving group.

8. Process as claimed in claim 7 wherein X represents a halogen atom or an alkanesulphonyl group.

9. Process for the preparation of a compound as claimed in claim 1, which comprises reacting a pyrimidinyl hydrazine of formula V

with a substituted acetic acid derivative of formula VI

wherein A, B, D, R¹, R², R³, R⁴ and R⁵ are as defined in claim 1.

10. Process for the preparation of a compound as claimed in claim

1, which comprises reacting a 2-pyrimidinyl hydrazine of formula V as defined in claim 9 with a methoxycarbonyl acetyl halide, followed by reaction with a 2-substituted compound of formula VII:

wherein X represents a leaving group.

11. Process as claimed in claims 7, 9 or 10, which is carried out substantially as described in, respectively, Example 1, 2 or 3 herein.

12. A compound as claimed in claim 1, whenever prepared by a process as claimed in any one of claims 7 to 11.

13. Herbicidal composition which comprises a compound as claimed in any one of claims 1-6 and 12 is association with a carrier and/or a surface-active agent.

14. Method of combating undesired plant growth at a locus, which comprises treating the locus with a compound as claimed in any one of claims 1-6 or 12, or a composition as claimed in claim 13.

15. Use of a compound as claimed in any one of Claims 1-6 or 12 in combating undesired plant growth.