GB2240976A - Pyridine derivatives - Google Patents

Abstract

Pyridine derivatives having the general formula (I): <IMAGE> and stereoisomers thereof, wherein R is optionally substituted alkyl containing 2 to 5 carbon atoms, R<1> is optionally substituted alkyl, alkynyl, cycloalkyl, cycloalkylalkyl, alkylcycloalkyl, alkenyl, cycloalkenyl, cycloalkenylalkyl, alkylcycloalkenyl, cycloalkylalkynyl, cycloalkylalkenyl containing 4 to 8 carbon atoms; or R<1> is the group-(CH2)m-C=C-Y(II),-(CH2) n-C=C-Y (III) or -(CH2)p-Y (IV) wherein Y is optionally substituted phenyl, m is 0 to 2, n is 0 to 2 and p is 2 to 4; R<2> and R<3> are hydrogen, alkyl containing 1 to 4 carbon atoms, halogen, alkylamino containing 1 to 4 carbon atoms, cyano, amide, sulphone or alkoxy containing 1 to 4 carbon atoms, provided that R<2> and R<3> are not both hydrogen; and R<4> is hydrogen, alkyl containing 1 to 4 carbon atoms, alkenyl containing 3 to 4 carbon atoms, or alkenyl containing 3 to 4 carbon atoms and agrocemically acceptable salts, acylates and metal complexes thereof have plant growth regulating activity.

Description

PYRIDINE DERIVATIVES This invention relates to pyridine derivatives useful as plant growth regulating agents, to processes for preparing them, to compositions containing them and to methods of regulating plant growth using them.

According to the present invention there is provided a pyridine derivative having the general formula (I)

and stereoisomers thereof, wherein R is optionally substituted alkyl containing 2 to 5 carbon atoms, R1 is an optionally substituted alkyl, alkynyl, cycloalkyl, cycloalkylalkyl, alkylcycloalkyl group, each of said groups containing a total of from 4 to 8 carbon atoms; or is an optionally substituted alkenyl, cyc oalkenyl, cycloalkenylalkyl, alkylcycloalkenyl, cycloalkylalkynyl, cycloalkylalkenyl group, each of said groups containing a total of from 4 to 8 carbon atoms; or alternatively R1 is the group - (cm,) - C =- C - Y (11) - 2)n - C = C - Y (III) - (CH2)p - Y (IV) wherein Y is an optionally substituted phenyl group, m is an integer from 0 to 2, n is an integer from 0 to 2 and p is an integer from 2 to 4;R2 and R3 are the same or independently hydrogen, alkyl containing 1 to 4 carbon atoms, halogen, alkylamino containing 1 to 4 carbon atoms, cyano, amide, sulphone or alkoxy containing from 1 to 4 carbon atoms, provided that R2 and R3 are not both hydrogen; and R4 is hydrogen, an alkyl group containing from 1 to 4 carbon atoms, an alkenyl group containing from 3 to 4 carbon atoms, or an alkynyl group containing from 3 to 4 carbon atoms and agrochemically acceptable salts, acylates and metal complexes of the compounds of the formula (I) wherein R2 is hydrogen.

The compounds of the invention may contain one or more chiral centres. Such compounds are generally obtained in the form of racemic mixtures. However, these and other mixtures can be separated into the individual isomers by methods known in the art, and this invention embraces such isomers.

R is preferably the group

wherein X is hydrogen or halogen; R5 is hydrogen, methyl or ethyl. When X is halogen, it is preferably chlorine or fluorine. Specific examples of R are isopropyl, tertiary butyl and l,l-dimethylpropyl.

When R1 is an optionally substituted cycloalkylalkyl or cycloalkenylalkyl group (that is a group in which the cycloalkyl or cycloalkenyl moiety is linked to the rest of the molecule through an alkyl chain), the optionally substituted cycloalkyl or cycloalkenyl group preferably contains from 3 to 6, for example, from 3 to 5 ring carbon atoms. Optional substituents which may be present in the cycloalkyl or cycloalkenyl ring include halogen and lower alkyl (for example C1 to C4 alkyl).

Optional substituents which may be present in the group R1 include halogen, especially monohalogen, for example, chlorine or fluorine.

When R1 is an alkenyl group, it is preferably a group: -(CH2) - CH = CH - R6 2 n where R6 is an optionally substituted alkyl group containing from 1 to 6 carbon atoms, or an optionally substituted cycloalkyl or cycloalkylalkyl group containing from 3 to 6 carbon atoms and n is an integer from 0 to 2, especially 0 or 1. Especially preferred alkenyl R1 groups have the formula 6 - CH = CH - R wherein R6 is an optionally substituted alkyl group containing from 1 to 6 carbon atoms.

When R1 is an alkynyl group it is preferably a group: - (CH2)m - C - C - R7 7.

wherein R7 is an optionally substituted alkyl group containing from 1 to 6 carbon atoms, or an optionally substituted cycloalkyl or cycloalkylalkyl group containing from 3 to 6 carbon atoms and m is an integer from 0 to 2, especially 0 or 1. Especially preferred alkynyl R2 groups have the formula - C - C - R7 7.

wherein R is an optionally substituted alkyl group containing from 2 to 6 carbon atoms, and especially from 3 to 4 carbon atoms.

As examples of optional substituents which may be present in the phenyl group, Y, there may be mentioned one or more substituents selected from halogen, for example chlorine or fluorine; alkyl, for example, lower alkyl; cycloalkyl, for example, cycloalkyl containing from 3 to 6 carbon atoms; alkoxy, for example, lower alkoxy; haloalkyl, for example, lower haloalkyl; lower alkoxycarbonyl, for example, -COOCH3; lower alkylcarbonyl for example, -CO.CH3; nitro; and cyano. The term "lower" as applied to the above groups indicates that the group contains from 1 to 6 carbon atoms, and preferably from 1 to 4 carbon atoms.

Specific examples of the group Y are phenyl, o-, mand p-chlorophenyl; o-, m- and p-fluorophenyl; dichlorophenyl (for example, 2,4-dichlorophenyl); difluorophenyl (for example, 2,4-difluorophenyl); o-, m-, and p-methylphenyl; o-, m-, and p-trifluoromethylphenyl; o-, m-, and p-methoxyphenyl; chlorofluorophenyl (for example, 3-chloro-4-fluoro); o-, m-, and p-methoxyphenyl; and o-, m- and p-nitrophenyl.

Preferred R2 and R3 groups are hydrogen, methyl, ethyl, propyl, butyl, methylamine, methoxy, ethoxy, fluorine, chlorine, bromine or iodine. An especially preferred group is cyano.

Preferred R4 groups are hydrogen, methyl, ethyl, allyl or propargyl. Hydrogen is especially preferred.

The present invention includes agrochemically acceptable salts, acylates and metal complexes of the compounds of formula (I) wherein R4 is hydrogen. As examples of acylates there may be mentioned, for example, acetates or benzoates. As examples of salts there may be mentioned for example toluene sulphonate salts, dodecylbenzene sulphonate salts, hydrochloride salts, hydrobromide salts and orthophosphate salts. Without limitation of the generality of the above statement, the present invention also includes any compound which breaks down in agrochemical use to a compound of formula (I).

An example of the compounds of the invention is presented in Table 1 in which the values for R, R1, R2, R3 and R4 in the general formula (I) above are as indicated.

TABLE 1

Compd R R1 R21iR3 R4 N. pt.

No. i R1 R2 i 1 -CH(CH3)2 -C~C < CN b H H 96-99 I I Compounds of general formula (I) above wherein R4 is hydrogen and R, R11 R2 and R3 are as defined may be prepared by reacting a compound of general formula (V)

with an organometallic compound which may be represented by the general formula (VI) Rln (VI) where M is a suitable metal, for example lithium, magnesium, titanium or zirconium.

The reaction conveniently takes place in a solvent such as diethylether (ether), tetrahydrofuran or dichloromethane at -800C to +800C in an inert atmosphere.

The product is obtained by quenching with a proton donor.

When M is magnesium, the organometallic compound is more specifically R1-Mg-halogen. When M is titanium, the organometallic compound is more specifically R1-Ti(O-alkyl)3. When M is zirconium, the organometallic compound is more specifically Rl-Zr-(O-alkyl)3.

The compounds of general formula (I) wherein R is hydrogen may also be prepared by reacting a ketone of general formula (VII), wherein R and R1 are as defined with an organometallic compound which may be represented by the general formula (VIII) wherein M is a suitable metal, for example, lithium and R2 and R3 are as defined

The reaction preferably takes place in a suitable solvent such as diethylether (ether) or tetrahydrofuran at a temperature of from -1200C to +800C and in an inert atmosphere. The product is obtained by quenching with a suitable proton donor.

The compounds of general formula (VII) wherein R1 is optionally substituted -C-C-alkyl or the group (II) where m is 0 may be prepared by reaction of a compound of formula (IX) :

where X is halogen and R is as defined, with the compound H-CC-alkyl or H-CC-Y in the presence of a base and a palladium catalyst.

Olefinic alcohols wherein R1 is the group -CH=CH-Y wherein Y is as defined above may be made by the reduction of the corresponding acetylenic alcohol wherein R1 is -C-C-Y. Suitable reducing agents include hydrogen in the presence of a suitable catalyst such as palladium on a support such as carbon (for example a Lindlar catalyst); or a metal hydride reducing agent such as lithium aluminium hydride. "Red-Al" (sodium bis [2-methoxyethoxy] aluminium hydride) or sodium borohydride/palladium (II) chloride in a suitable solvent such as ether or tetrahydrofuran.

Similarly, compound of formula (I) wherein R1 is the group -CH2-CH2-Y where Y is as defined above, may be made by the complete reduction of the corresponding acetylenic alcohol, -C--C-Y. Suitable reducing agents are palladium, platinum or rhodium on a support such as carbon and in a suitable solvent such as methanol, ethanol or acetic acid.

The ethers (wherein R4 is alkyl) and acylates of the invention may be made from the corresponding hydroxy compound by reaction with the appropriate halide, acid chloride or acid anhydride in the presence of a suitable base.

The plant growth regulating effects of the compounds are manifested as, for example, by a stunting or dwarfing effect on the vegetative growth of woody and herbaceous mono- and dicotyledonous plants. Such stunting or dwarfing may be useful, for example, in peanuts, cereals such as rice, wheat and barley, oil seed rape, field beans, sunflowers, potatoes and soya bean where reduction in stem height, with or without further advantageous effects such as stem strengthening, thickening and shortening, internode shortening, increased buttress root formation and more erect stem and leaf orientation, may reduce the risk of lodging and may also permit increased amounts of fertiliser to be applied. The stunting of woody species is useful in controlling the growth of undergrowth under power lines etc.Compounds which induce stunting or dwarfing may also be useful in modifying the stem growth of sugar cane thereby increasing the concentration of sugar in the cane at harvest; in sugar cane, the flowering and ripening may be controllable by applying the compounds. Stunting of peanuts can assist in harvesting. Growth retardation of grasses can help maintenance of grass swards. Examples of suitable grasses are Stenotaphrum secundatum (St. Augustine grass), Cynosurus cristatus, Lolium multiflorum and perenne, Agrostis tenuis, Cynodon dactylon (Bermuda grass), Dactylis glomerata, Festuca spp. (eg, Festuca rubra) and Poa spp. (eg, Poa pratense). The compounds may stunt grasses without significant phytotoxic effects and without deleteriously affecting the appearance (particularly the colour) of the grass; this makes such compounds attractive for use on ornamental lawns and on grass verges.They may also have an effect on flower head emergence in, for example,grasses. The compounds can also stunt weed species present in the grasses; examples of such weed species are sedges (eg, Cyperus spp.) and dicotyledonous weeds (eg, daisy, plantain, knotweed, speedwell, thistle, docks and ragwort). The growth of non-crop vegetation (eg, weeds or cover vegetation) can be retarded thus assisting in the maintenance of plantation and field crops. In fruit orchards, particularly orchards subject to soil erosion, the presence of grass cover is important. However excessive grass growth requires substantial maintenance.

The compounds of the invention could be useful in this situation as they could restrict growth without killing the plants which would lead to soil erosion; at the same time the degree of competition for nutrients and water by the grass would be reduced and this could result in an increased yield of fruit. In some cases, one grass species may be stunted more than another grass species; this selectivity could be useful, for example, for improving the quality of a sward by preferential suppression of the growth of undesirable species.

The dwarfing may also be useful in miniaturising ornamental, household, garden and nursery plants (eg, poinsettias, chrysanthemums, carnations, tulips and daffodils).

As indicated above, the compounds can also be used to stunt woody species. This property can be used to control hedgerows or to shape or reduce the need for pruning, of fruit trees (eg, apples, pears, cherries, peaches, vines etc).

The plant growth regulating effect may (as implied above) manifest itself in an increase in crop yield; or in an ability in orchards and other crops to increase fruit set, pod set and grain set. Some coniferous trees are not significantly stunted by the compounds so the compounds could be useful in controlling undesirable vegetation in conifer nurseries.

In the potato, vine control in the field and inhibition of sprouting in the store may be possible.

In addition the compounds may be useful as absicision agents resulting in thinning of fruit on the tree and an increase in fruit quality.

Other plant growth regulating effects caused by the compounds include alteration of leaf angle and changes in leaf morphology (both of which may permit increased light interception and utilization) and promotion of tillering in monocotyledonous plants. Improved light interception is of value in all major world crops, eg, wheat, barley, rice, maize, soya, sugarbeet, potatoes, plantation crops and orchard crops. The leaf angle effect may be useful for example in altering the leaf orientation of, for example, potato crops thereby letting more light into the crops and inducing an increase in photosynthesis and tuber weight. By increasing tillering in monocotyledonous crops (eg, rice), the number of flowering shoots per unit area may be increased thereby increasing the overall grain yield of such crops. In addition better control and modification of hierarchical relationships is possible both in vegetative and reproductive stages of monocotyledonous and dicotyledonous plant growth, especially in cereals such as wheat, barley, rice and maize, whereby the number of flowering shoots per unit area may be increased and the size distribution of grains within the ear may be modified in such a way as to increase yield. In the treatment of rice plants, or rice crops the invention compounds can be applied, eg, as granules or a granular formulation, for example as slow release granules, to nursery boxes, paddy water and other like cultivation loci and media.In grass swards, especially amenity grass, an increase in tillering could lead to a denser sward which may result in increased resilience in wear; and to increased yields and better quality of forage grass, eg, improved digestability and palatability.

The treatment of plants with the compounds can lead to the leaves developing a darker green colour. In dicotyledonous plants such as soyabean and cotton, there may be promotion of sideshooting.

The compounds may inhibit, or at least delay, the flowering of sugar beet (and thereby may increase sugar yield) or otherwise modify the flowering patterns in many other crops. They may also reduce the size of sugar beet without reducing significantly the sugar yield thereby enabling an increase in planting density to be made.

Similarly in other root crops (eg, turnip, swede, mangold, parsnip, beetroot, yam and cassava) it may be possible to increase the planting density. The compounds could be useful in restricting the vegetative growth of cotton thereby leading to an increase in cotton yield. Crop yields may also be increased by improvement of the harvest index (ie. the harvested yield as a proportion of the total dry matter produced) by altering dry matter partitioning. This applies to all the aforementioned root, pod, cereal, tree, plantation and orchard crops.

The compounds may be useful in rendering plants resistant to stress since the compounds can delay the emergence of plants grown from seed, shorten stem height and delay flowering; these properties could be useful in preventing frost damage in countries where there is significant snow cover in the winter since then the treated plants would remain below snow cover during the cold weather. Further the compounds may cause drought or cold resistance in certain plants.

When applied as seed treatments at low rates the compounds can have a growth stimulating effect on plants.

It is to be understood that not all the compounds of the present invention will necessarily show all the above mentioned plant growth regulating effects. Thus whilst there may be advantages in compounds which have a broad spectrum of plant growth regulating effects against a wide range of species, compounds having a high specific activity with respect to a particular species and/or plant growth regulating effect may also be of great benefit.

In carrying out the plant growth regulating method of the invention, the amount of compound to be applied to regulate the growth of plants will depend upon a number of factors, for example the particular compound selected for use, and the identity of the plant species whose growth is to be regulated. However, in general an application rate of 0.1 to 15, preferably 0.1 to 5, kg per hectare is used.

With the use of biodegradable polymeric slow release granules rates of 1 to 10g per hectare are feasible; whilst electrodynamic spraying techniques may also deploy lower rates of application. However, on certain plants even application rates within these ranges may give undesired phytotoxic effects. Routine tests may be necessary to determine the best rate of application of a specific compound for any specific purpose for which it is suitable.

The compounds may be used as such for plant growth regulating purposes but are more conveniently formulated into compositions for such usage. The invention thus provides a plant growth regulating composition comprising a compound of general formula (I) as hereinbefore defined, or a salt or metal complex thereof; and, optionally, a carrier or diluent.

The invention also provides a method of regulating plant growth, which comprises applying to the plant, to seed of a plant or to the locus of a plant or seed, a compound, or a salt or metal complex thereof, as hereinbefore defined, or a composition combining the same.

The compounds, salts, metal complexes, ethers and esters can be applied in a number of ways, for example they can be applied, formulated or unformulated, directly to the foliage of a plant, or they can be applied also to bushes and trees, to seeds or to other medium in which plants, bushes or trees are growing or are to be planted, or they can be sprayed on, dusted on or applied as a cream or paste formulation, or they can be applied as a vapour; or as slow release granules. Application can be to any part of the plant, bush or tree, for example to the foliage, stems, branches or roots, or to soil surrounding the roots, or to the.seed before it is planted; or to the soil generally, to paddy water or to hydroponic culture systems. The invention compounds may also be injected into plants or trees and they may also be sprayed onto vegetation using electrodynamic spraying techniques.

The term "plant" as used herein includes seedlings, bushes and trees.

The compounds are preferably used for agricultural and horticultural purposes in the form of a composition.

The type of composition used in any instance will depend upon the particular purpose envisaged.

The compdsitions may be in the form of dusting powders or granules comprising the active ingredient and a solid diluent or carrier, for example fillers such as kaolin, bentonite, kieselguhr, dolomite, calcium carbonate, talc, powdered magnesia, Fuller's earth gypsum, Hewitt's earth, diatomaceous earth and China clay. Such granules can be preformed granules suitable for application to the soil without further treatment. These granules can be made either by impregnating pellets of filler with the active ingredient or by pelleting a mixture of the active ingredient and powdered filler.

Compositions for dressing seed, for example, may comprise an agent (for example a mineral oil) for assisting the adhesion of the composition to the seed; alternatively the active ingredient can be formulated for seed dressing purposes using an organic solvent (for example Nmethylpyrrolidone or dimethylformamide).

The compositions may also be in the form of dispersible powders, granules or grains comprising a wetting agent to facilitate the dispersion in liquids of the powder or grains which may contain also fillers and suspending agents.

The aqueous dispersions or emulsions may be prepared by dissolving the active ingredient(s) in an organic solvent optionally containing wetting, dispersing or emulsifying agent(s) and then adding the mixture to water which may also contain wetting, dispersing or emulsifying agent(s). Suitable organic solvents are ethylene dichloride, isopropyl alcohol, propylene glycol, diacetone alcohol, toluene, kerosene, methylnaphthalene, the xylenes, trichloroethylene, furfuryl alcohol, tetrahydrofurfuryl alcohol, and glycol ethers (eg, 2ethoxyethanol and 2-butoxyethanol).

The compositions to be used as sprays may also be in the form of aerosols wherein the formulation is held in a container under pressure in the presence of a propellant, eg, fluorotrichloromethane or dichlorodifluoromethane.

The compounds can be mixed in the dry state with a pyrotechnic mixture to form a composition suitable for generating in enclosed spaces a smoke containing the compounds.

Alternatively, the compounds may be used in a microencapsulated form. They may also be formulated in biodegradable polymeric formulations to obtain a slow, controlled release of the active substance.

By including suitable additives, for example additives for improving the distribution, adhesive power and resistance to rain on treated surfaces, the different compositions can be better adapted for.various utilities.

The compounds can be used as mixtures with fertilisers (eg, nitrogen-, potassium- or phosphoruscontaining fertilisers). Compositions comprising only granules of fertiliser incorporating, for example coated with, the compound are preferred. Such granules suitably contain up to 25% by weight of the compound. The invention therefore also provides a fertiliser composition comprising the compound of general formula (I) or a salt or metal complex thereof.

The compositions may also be in the form of liquid preparations for use as dips or sprays which are generally aqueous dispersions or emulsions containing the active ingredient in the presence of one or more surfactants eg, wetting agent(s), dispersing agent(s), emulsifying agent(s) or suspending-agent(s); or which are spray formulations of the kind suitable for use in electrodynamic spraying techniques. The foregoing agents can be cationic, anionic or non-ionic agents. Suitable cationic agents are quaternary ammonium compounds, for example cetyltrimethylammonium bromide.

Suitable anionic agents are soaps, salts of aliphatic monoesters of sulphuric acid (for example sodium lauryl sulphate), and salts of sulphonated aromatic compounds (for example sodium dodecylbenzenesulphonate, sodium, calcium or ammonium lignosulphonate, butylnaphthalene sulphonate, and a mixture of sodium diisopropyl- and triisopropyl-naphthalene sulphonates).

Suitable non-ionic agents are the condensation products of ethylene oxide with fatty alcohols such as oleyl or cetyl alcohol, or with alkyl phenols such as octyl- or nonyl-phenol and octylcresol. Other non-ionic agents are the partial esters derived from long chain fatty acids and hexitol anhydrides, the condensation products of the said partial esters with ethylene oxide, and the lecithins. Suitable suspending agents are hydrophilic colloids (for example polyvinylpyrrolidone and sodium carboxymethylcellulose), and the vegetable gums (for example gum acacia and gum tragacanth).

The compositions for use as aqueous dispersions or emulsions are generally supplied in the form of a concentrate containing a high proportion of the active ingredient(s), and the concentrate is to be diluted with water before use. These concentrates often should be able to withstand storage for prolonged periods and after such storage be capable of dilution with water in order to form aqueous preparations which remain homogeneous for a sufficient time to enable them to be applied by conventional and electrodynamic spray equipment. The concentrates may conveniently contain up to 95%, suitably 10-85%, for example 25-60%, by weight of the active ingredient(s).These concentrates suitably contain organic acids (eg, alkaryl or aryl sulphonic acids such as xylenesulphonic acid or dodecyl benzenesulphonic acid) since the presence of such acids can increase the solubility of the active ingredient(s) in the polar solvents often used in the concentrates. The concentrates suitably contain also a high proportion of surfactants so that sufficiently stable emulsions in water can be obtained. After dilution to. form aqueous preparations, such preparations may contain varying amounts of the active ingredient(s) depending upon the intended purpose, but an aqueous preparation containing 0.0005% to 10%, or 0.01% to 10%, by weight of active ingredient(s) may be used.

The compositions of this invention can comprise also one or more additional compound(s) having biological activity, eg, compounds having similar or complementary fungicidal or plant growth activity or compounds having plant growth regulating, herbicidal or insecticidal activity.

The additional fungicidal compound can be, for example, one which is capable of combating ear diseases of cereals (eg,wheat) such as Septoria, Gibberella and Helminthosporium spp., seed and soil borne diseases and downy and powdery mildews on grapes and powdery mildew and scab on apple etc. Examples of suitable additional fungicidal compound are imazalil, benomyl, carbendazim, thiophanate-methyl, captafol, captan, sulphur, triforine, dodemorph, tridemorph, pyrazophos, furalaxyl, ethirimol, tecnazene, dimethirimol, bupirimate, chlorothalonil, vinclozolin, procymidone, iprodione, metalaxyl, forsetylaluminium, carboxin, oxycarboxin, fenarimol, nuarimol, fenfuram, methfuroxan, nitrotal-isopropyl, triadimefon, thiabendazole, etridiazole, triadimenol, biloxazol, dithianon, binapacryl, quinomethionate, guazatine, dodine fentin acetate, fentin hydroxide, dinocap, folpet, dichlofluanid, ditalimphos, kitazin, cycloheximide, dichlobutrazol, a dithiocarbamate, a copper compound, a mercury compound, l-(2-cyano-2-methoxyiminoacetyl)-3-ethyl urea, fenaponil, ofurace, propiconazole, etaconazole and fenpropemorph and fenpropidine.

The compounds of general formula (I) can be mixed with soil, peat or other rooting media for the protection of plants against seed-borne, soil-borne or foliar fungal diseases.

Suitable additional insecticides are Pirimor, Croneton, dimeth- oate, Metasystox, pyrethroid insecticides and formothion.

The other, additional, plant growth regulating compound can be one which controls weeds or seedhead formation, improves the level or longevity of the plant growth regulating activity of the compounds of general formula (I), selectively controls the growth of the less desirable plants (eg, grasses) or causes the compound of general formula (I) to act faster or slower as a plant growth regulating agent. Some of these other agents will also be herbicides.

Examples of suitable plant growth regulating compounds, which can display synergy in admixture, or use, with the invention compounds are the gibberellins (eg, GA3, GA4 or GA7), the auxins (eg, indoleacetic acid, indolebutyric acid, naphthoxyacetic acid or naphthylacetic acid), the cytokinins (eg, kinetin, diphenylurea, benzimidazole, benzyladenine or benzylaminopurine), phenoxyacetic acids (eg, 2,4-D or MCPA), substituted benzoic acids (eg, triiodobenzoic acid), morphactins (eg, chlorfluorecol), maleic hydrazide, glyphosate, glyphosine, long chain fatty alcohols and acids, dikegulac, fluoridamid, mefluidide, substituted quaternary ammonium and phosphonium compounds (eg, chlormequat* chlorphonium or mepiquat chloride*), ethephon, carbetamide, methyl-3,6dichloroanisate, daminozide*, asulam, abscisic acid, isopyrimol, l-(4-chlorophenyl)-4,6-dimethyl-2-oxo-1,2- dihydropyridine-3-carboxylic acid, hydroxybenzonitriles (eg, bromoxynil), difenzoquat*, benzoylprop-ethy 3,6dichloropicolinic acid, fenpentezol, triapenthanol, flurpirimidol, paclobutrazol, tetcyclacis and tecnazene.

Synergy will be most likely to occur with those of the foregoing which are quaternary ammonium compounds and with those marked with an asterisk.

For certain applications, for example in the injection of the compounds of the invention into trees or plants, it is desirable that the compounds have a relatively high solubility in water, for example a solubility in excess of 30 parts per million. The compounds may alternatively be injected into the tree in the form of an organic solution, for example a solution in a lower alcohol.

For certain applications it is also desirable that the compound has a low persistancy in soil to prevent carry-over to adjacent crops or even crops planted subsequently in the same soil. Preferably the compound for use in such applications has a half life in the soil of less than 20 weeks.

The invention is illustrated by the following examples. The NMR characterisation of the compounds is given in terms of EH at 270 MHz and the spectra were recorded in CDC13 with tetramethylsilane as internal standard (unless otherwise stated).

EXAMPLE 1 Preparation of 2-methyl-5-phenyl-3-(3-cyanopyrid5-yl)pent-4-yn-3-ol (Compound No. 1 of Table 1) Step A : Preparation of 3-bromo-5-carboxyethylpyridine.

Method Thionyl chloride (10.9ml;0.15mol) was added slowly to absolute ethanol at between -300C to -100C. The reaction mixture was allowed to warm to room temperature and bromonicotinic acid (10.lg;0.05mol) was added in a single portion. The reaction mixture was heated at reflux for 6 hours, then allowed to stand at room temperature for several days.

The reaction mixture was concentrated under reduced pressure and the residue was partitioned between sodium bicarbonate solution and methylene chloride. The aqueous layer was further extracted twice with methylene chloride.

The combined organic layers were dried over magnesium sulphate before being concentrated under reduced pressure to yield a yellow oil which solidified on standing.

Yield 10.76g = 94% 1z NMR : 9.2 (1H,s); 8.8 (1H,s); 8.4 (lH,s); 4.4 (2H,q); 1.4 (3H,t) Step B : Preparation of 5-bromonicotinamide.

Method 5-Bromo-5-carboxyethylpyridine (2.3g;0.01mol) was allowed to stand in concentrated ammonia solution (25ml) for 3 days at room temperature. The solid precipitate present was collected by filtration.

Yield 1.23g = 61% 1H NMR : 8.9 (lH,m); 8.8 (1H,m); 8.4 (lH,m); 8.2 (lH,bs) (d6 DMSO) 7.7 (lH,bs) MS : 202 and 200 (2xM+), 186, 184, 158, 156, 28 Step C : Preparation of 5-bromo-3-cyanopyridine.

Method Phosphorous oxychloride (50ml) was added to a suspension of 5-bromonicotinamide (3.27g;16mmol) in chloroform (200ml), and the reaction mixture heated at reflux for 6 hours. The reaction mixture was concentrated under reduced pressure, carefully quenched with water and the organic layer collected. The aqueous layer was extracted with chloroform. The combined organic layers were dried with magnesium sulphate and concentrated under reduced pressure to yield a colourless oil. This was placed under high vacuum and yielded 3-bromo-5-cyanopyridine as a white solid.

Yield 2.39 = 82% 1H NMR : 8.9 (1H,d); 8.8 (1H,m); 8.1 (lH,m) MS : 182 and 184 (M+), 103(100%), 76, 75 Step D : Preparation of 2-methyl-5-phenylpent-4-yn-3-one Method The preparation was performed under a nitrogen atmosphere. Isobutyryl chloride (20.2g, 0.19mol) and phenylacetylene (19.4g, 0.19mol) were stirred together in triethylamine (100ml). Copper (I) iodide (0.3g) and bis(triphenylphosphine) palladium (II) chloride (0.3g) were added and the reaction mixture stirred for 30 minutes after which time a strong exotherm occurred raising the temperature to 800C and causing the reaction to set solid.

Further triethylamine (400ml) was added and the solid broken up. The suspension was stirred at room temperature for a further 24 hours. Methanol (100ml) was added and the reaction mixture was stirred for 10 minutes before concentration under reduced pressure. Water was added to the residue and the solution was extracted with ether three times. The combined organic layers were washed with water, dried over magnesium sulphate and concentrated under reduced pressure. The residue was distilled (30mmHg) collecting the fraction boiling between 163-169 C.

Yield 17.lg = 52% H NMR : 7.6 (2H,m); 7.4 (3H,m); 2.7 (1H,m); 1.3 (6H,d) Step E : Preparation of 2-methyl-5-phenyl-3-(3-cyanopyrid 5-yl)pent-4-yn-3-ol.

Method The preparation was performed under a nitrogen atmosphere. Toluene was added to 5-bromo-3- cyanopyridine (406mg:2.21mmol) which was hydroscopic and the suspension concentrated under reduced pressure to azeotrope residual water. Dry ether (30ml) was added to the residue and the solution cooled to -780C. Butyllithium (0.87ml of 2.5M in hexanes:2.17mmol) was added dropwise causing a red colouration of the solution. On completion, a solution of 2-methyl-5-phenylpent-4-yn- 3-one (0.292;2.17mmol) from step D in tetrahydrofuran (4ml) was added dropwise and the solution allowed to warm to room temperature over 6 hours.

The reaction was quenched with saturated ammonium chloride solution and the organic layer separated. The aqueous layer was washed twice with ether and the combined organic fractions washed with water, dried over magnesium sulphate and concentrated under reduced pressure. The residue was taken up in hexane and the solids removed by filtration.

The filtrate was concentrated under reduced pressure and the residue purified by preparative HPLC on silica gel, eluting with ether:hexane (1:1).

Yield 75mg = 12% 1H NMR : 9.1 (lH,m); 8.8 (lH,m); 8.2 (lH, m); 7.5 (2H, m); 7.3 (3H,m); 2.8 (lH,s); 2.2 (lH,m) 1.1 (3H,d); 1.0 (3H,d) MS : 276 (M+), 233 (100%), 131.

EXAMPLE 2 Compound No. 1 of Table 1 was tested on a retardant test against two cereal species. Retardation is commercially the most important plant growth regulator effect and indicates that the compound is acting as a plant growth regulator potentially leading to other direct or indirect effects such as yield enhancement.

Intermediate Retardant Test Methodology Two species were involved in this test, RICE and SPRING BARLEY. The variety and growth stages at treatment are outlined in Table II. The compound was applied at one rate 2000ppm (ie. 2 kg/ha at a field volume of 1000 1/aha) as an overall spray. This gives a foliar and root component in the test, ie. this test will detect the activity of both root and foliar acting compounds. The rice was grown in 4 inch (10.2cm) 'paddy' pots, ie. the roots and bottom of the stems were immersed in water under conditions corresponding to those in paddy fields. Spring barley was grown in 4 inch (10.2cm) pots. The plants were assessed for height to top-most ligule at approximately 28 days after treatment. The results are presented in Table III. In each case the height of the plants treated with the compound is compared to the height of the plants treated with the formulation blank (ie. the control plants) for that species. The results are presented as a percentage reduction in height compared to the formulation blank. A blank indicates that the compound was substantially inactive as a retardant at that particular rate of application.

TABLE II PLANT MATERIAL FOR INTERMEDIATE RETARDANT TEST

Species Variety Growth stage No plants Compost at treatment per pot type Spring Atem 3 leaves 4 JIP 1 Barley i Rice Ishikari 3-4 leaves 2 SM2:JIPl JIP 1 = John Innes Potting Compost SM2 = a mixture of loam and grit TABLE III Percentage Reduction in Height of Rice or Spring Barley (compared to formulation blank)

Species Compound No. Rice Spring Barley 1 49 14 The manner in which the compounds of the present invention may be formulated into compositions suitable for application is shown generally in the following indicative illustrations numbered as Examples 3 to 12 EXAMPLE 3 An emulsifiable concentrate is made up by mixing the following ingredients, and stirring the mixture until all the constituents were dissolved.

Compound of Table 1 10 % Calcium dodecylbenzensulphate 5 % "SYNPERONIC" NP13 5 % "AROMASOL" H 80 % EXAMPLE 4 A composition in the form of grains readily dispersible in a liquid, eg. water, is prepared by grinding together the first three ingredients in the presence of added water and then mixing in the sodium acetate. The resultant mixture is dried and passed through a British Standard mesh sieve, size 44-100, to obtain the desired size of grains.

Compound of Table 1 50 % "Dispersol" T 25 % "SYNPERONIC" NP5 1.5 % Sodium acetate 23.5 % EXAMPLE 5 The following ingredients are ground together to produce a powder formulation readily dispersible in liquids.

Compound of Table 1 45 % "Dispersol" T 5 % "SYNPERONIC" NX 0.5 % "Cellofas" B600 2 % China clay GTY powder 47.5 % EXAMPLE 6 The active ingredient is dissolved in acetone and the resultant liquid is sprayed on to the granules of attapulgite clay. The solvent is then allowed to evaporate to produce a granular composition.

Compound of Table 1 5 % Attapulgite granules 95 % EXAMPLE 7 A composition suitable for use as a seed dressing is prepared by mixing the three ingredients.

Compound of Table 1 50 % Mineral Oil 2 % China Clay 48 % EXAMPLE 8 A dusting powder is prepared by mixing the active ingredient with talc.

Compound of Table I 5 % Talc 95 % EXAMPLE 9 A flowable formulation is prepared by bead-milling the constituents set out below and then forming an aqueous suspension of the ground mixture with water.

Compound of Table 1 40 % "Dispersol" T 4 % "SYNPERONIC" NP5 1 % Water 55 % EXAMPLE 10 A dispersible powder formulation is made by mixing together the ingredients set out below and then grinding the mixture until all were thoroughly mixed.

Compound of Table I 25 % "Aerosol" OT/B 2 % "Dispersol'1 A.C 5 % China clay 28 % Silica 40 % EXAMPLE 11 This Example illustrates the preparation of a dispersible powder formulation. The ingredients are mixed and the mixture then ground in a communution mill.

Compound of Table I 25 % "Perminal" BX 1 % "Dispersol" T 5 % Polyvinylpyrrolidone 10 % Silica 25 % China Clay 3.4 % EXAMPLE 12 The ingredients set out below are formulated into dispersible powder by mixing then grinding the ingredients.

Compound of Table I 25 % "Aerosol" OT/B 2 % "Dispersol" A 5 % China clay 68 % There now follows an explanation of the compositions or substances represented by the various Trade marks and Trade names mentioned above.

"SYNPERONIC" NP13 : a condensate of nonyl phenol (1 mole) with ethylene oxide (13 moles).

"AROMASOL" H : a solvent mixture of alkyl benzenes.

"DISPERSOL" T AND AC : a mixture of sodium sulphate and condensate of formaldehyde with sodium napthalene sulphonate.

"SYNPERONIC" NP5 : a condensate of nonyl phenol (1 mole) with naphthalene oxide (5.5 moles).

CELLOFAS B600 : a sodium carboxymethyl cellulose thickener.

Claims (3)

1. A pyridine derivative having the general formula (I)

and stereoisomers thereof, wherein R is optionally substituted alkyl containing 2 to 5 carbon atoms, R1 is an optionally substituted alkyl, alkynyl, cycloalkyl, cycloalkylalkyl, alkylcycloalkyl group, each of said groups containing a total of from 4 to 8 carbon atoms; or is an optionally substituted alkenyl, cycloalkenyl, cycloalkenylalkyl, alkylcycloalkenyl, cycloalkylalkynyl, cycloalkylalkenyl group, each of said groups containing a total of from 4 to 8 carbon atoms; or alternatively R1 is the group - (CH2)m - C C - Y (Il) - (CH2)n - C = C - Y (III) - (CH2)p - Y (IV) wherein Y is an optionally substituted phenyl group, m is an integer from 0 to 2, n is an integer from 0 to 2 and p is an integer from 2 to 4;R2 and R3 are the same or independently hydrogen, alkyl containing 1 to 4 carbon atoms, halogen, alkylamino containing 1 to 4 carbon atoms, cyano, amide, sulphone or alkoxy containing from 1 to 4 carbon atoms, provided that R2 and R3 are not both hydrogen; and R4 is hydrogen, an alkyl group containing from 1 to 4 carbon atoms, an alkenyl group containing from 3 to 4 carbon atoms, or an alkynyl group containing from 3 to 4 carbon atoms and agrochemically acceptable salts, acylates and metal complexes of the compounds of the formula (I) wherein R2 is hydrogen.

2. A plant growth regulating composition comprising a plant growth regulating amount of a pyridine derivative according to claim 1 and an agrochemically acceptable carrier or diluent.

3. A method of regulating plant growth which comprises applying to the plant, to the seed of the plant, or to the locus of the plant or seed, a plant growth regulating amount of a pyridine derivative according to claim 1.