AU648626B2

AU648626B2 - Substituted 1,3-dithiane or oxathiane derivatives

Info

Publication number: AU648626B2
Application number: AU91041/91A
Authority: AU
Inventors: Alexander Andrew Kee; David Allen Pulman
Original assignee: Roussel Uclaf SA
Current assignee: Sanofi Aventis France
Priority date: 1990-12-19
Filing date: 1991-12-18
Publication date: 1994-04-28
Anticipated expiration: 2011-12-18
Also published as: BR9107171A; NO932258L; CZ114393A3; HUT65130A; KR930703289A; JPH06503825A; CA2098704A1; WO1992011254A1; GB9027571D0; EP0565550A1; FI932846A; FI932846A0; HU9301793D0; AU9104191A; NO932258D0

Description

HETEROCYCLIC PESTICIDAL COMPOUNDS

The present invention is concerned with a method of controlling pests such as arthropods, e.g. insects and acarine pests, helminths, e.g. nematodes, and molluscs e.g. slugs by contacting the pests with novel pesticides. The invention is also concerned with the novel pesticides used for controlling the pests and processes for making such pesticides.

European Patent Applications 294228 and 294229 disclose inter alia that 5-substituted dithianes with a substituted phenyl moiety or a C_{2 - 16} hydrocarbyl group at the 2-position have pesticidal activity. European Patent Application 102062 discloses inter alia that 5-disubstituted amino dithianes having a hydrocarbon or heterocyclic group at the 2-position have pesticidal activity.

It has been discovered that a class of novel 2,2,5-trisubstituted dithianes has pesticidal activity.

Accordingly, the present invention provides a method for controlling pests which comprises contacting the pest with a pesticidally effective amount of a compound of the formula (I):

which contains between 8 and 30 carbon atoms, and wherein Y is oxygen or a group S(O)m and m and n are independently selected from 0, 1 and 2; R^2a and R^2b are the same or different and each is selected from cyano, nitro, methyl optionally substituted by halo,a group S(O)_qR⁷ where q is 0, 1 or 2 and R⁷ is methyl or ethyl, or a group COR⁸ where R⁸ is hydrogen, hydroxy, C_1-4 alkoxy, C_1-4 alkyl optionally substituted by fluoro or a group NR⁹R¹⁰ wherein R⁹ and R¹⁰ are independently selected from hydrogen, methyl or ethyl; R^4a and R^4b, R^6a and R^6b are independently selected from hydrogen, methyl, cyano or trifluoromethyl, R^5a is a primary, secondary or tertiary C_2-5 alkyl group optionally substituted by halo or C_1-4 alkoxy, or a C_3-4 cycloalkyl group, or R^5a is a C_3-4 cycloalkyl group and R^5b is hydrogen, hydroxy, C_1-4 alkoxy, C_1-4 alkanoyloxy, or C_1-4 alkyl optionally substituted by alkoxy; or R^5a and R^5a form a gem di-methyl group or are linked together with the ring carbon to which they are attached to form a 3 to 5-membered ring that optionally contains a hetero atom or an olefinic bond and is optionally substituted by a C_1-4 alkyl group optionally substituted by halo.

By the term "halo" is meant fluoro, chloro, bromo or iodo.

By the term "hetero atom" is meant oxygen, sulphur (optionally present in an oxidised form) or nitrogen substituted by hydrogen or C_1-4 alkyl.

Preferably Y is oxygen or sulphur. Suitably R^2a and R^2b are the same or different and each is selected from methyl, ethyl, cyano or trifluoromethyl. Preferably R^2a is methyl.

Preferably R^4b is methyl or cyano.

Suitably R^4a, R^4b, R^6a and R^6b are each selected from hydrogen, or methyl, and preferably they are all hydrogen. Suitably R^5a is a secondary or tertiary C_2-5 alkyl group optionally substituted by fluoro or a cyclopropyl group. Preferably R^5a is tertiary butyl or 2,2,2-trifluoro-1-methylethyl.

Suitably R^5b is hydrogen, methyl or ethyl, preferably R^5b is hydrogen.

In accordance with another embodiment of the present invention there is provided a compound of the formula (I) wherein R^2a, R^4a, R^4b, R^5b, R^6a, R^6b, m and n are as hereinbefore defined and R^2b is cyano, nitro, a group S(O)q R⁷, a group COR⁸ wherein q, R⁷ and R⁸ are as hereinbefore defined, or a C_1-3 alkyl group substituted by halo.

The compounds of the formula (I) may exist in a number of stereoisomeric forms. The present invention encompasses both individual conformational and stereoisomers and mixtures thereof. The present invention also encompasses compounds of the formula (I), containing radioisotopes particularly those in which or one to three hydrogen atoms are replaced by tritium or one or more carbon atoms are replaced by ¹⁴C.

Preferred compounds of the invention include:

5(e)-t-Butyl-2(e)-methyl-1,3-dithiane-2(a)-carbonitrile

5(e)-t-Butyl-2(a)-methyl-1,3-dithiane-2(e)-carbonitrile

5(e)-t-Butyl-2(e)-methyl-1,3-dithiane-2(a)-carbonitrile-1(e)-oxide

5(e)-t-Butyl-2(e)-methyl-1,3-dithiane-2(a)-carbonitrile-1,1-dioxide

2(e)-Methyl-5(e)-(1-methyl-2,2,2-trifluoroethyl)-1,3-dithiane-2(a)-carbonitrile

5(e)-Cyclopropyl-2(e)-methyl-1,3-dithiane-2(a)-carbonitrile

5(e)-t-Butyl-2(e)-methyl-1,3-oxathiane-2(a)-carbonitrile

5(e)-t-Butyl-2(e)-methyl-1,3-oxathiane-2(a)-carbonitrile-3(a)-oxide

5(e)-t-Butyl-2(e)-methyl-1,3-oxathiane-2(a)-carbonitrile-3(e)-oxide

5(e)-t-Butyl-2(e)-methyl-1,3-oxathiane-2(a)-carbonitrile-3,3-dioxide The present invention also provides for the preparation of the compounds of the formula (I) by methods derived from those known in the art for the preparation of analogous compounds. Thus, the compounds may be prepared

(i) by the reaction of a compound of the formula (II):

wherein X is SH and Y¹ is SH or OH with a suitable aldehyde or ketone of the or a reactive derivative thereof, wherein the R substituents at the 2, 4, 5 and 6 positions are as hereinbefore defined and, if required, thereafter oxidizing one or two ring sulphur atoms.

The reaction is suitably carried out in the presence of a catalyst or of a dehydrating agent in a non-polar solvent at a non-extreme temperature. Suitable catalysts include a dimethyl formamide/dimethyl sulphate catalyst and catalysts such as sulphonic acids or perfluorinated resins thereof or Lewis acids such as boron trifluoride etherate, or stannic chloride or concentrated formic acid which also serves as the reaction medium. Suitable solvents include hydrocarbons such as benzene, toluene or xylene or chlorinated hydrocarbons such as dichloromethane. The reaction is normally performed between 0 and 200 and conveniently between 20 and 120 Suitable reactive derivatives of aldehydes and ketones include acetals and ketals.

The compounds of the formula (II) may be prepared from the corresponding diols wherein X and Y are hydroxy. Thus the dithiols may be prepared via the sulphonate derivatives (i.e., compounds of the formula (II) wherein X and Y are groups OSO„R wherein R¹¹ is C_1-4 alkyl or para-tolyl) and the hydroxythiols may be prepared via precursors of the formula (II) in which X is halo, particularly bromo, and Y is a protected hydroxy group, for example an acetoxy group.

This precursor is then reacted with an appropriate reagent for replacing the halo atom with sulphur, for example potassium thiocyanate or thioacetate, followed by alkaline hydrolysis. The preparation of the diols and their conversion to the corresponding dithiols can be carried out by methods known in the art.

The aldehydes and ketones reacted with the compounds of the formula (II) are either known in the literature or are prepared by literature methods.

(ii) when it is desired to prepare a compound of the formula (I) when one of R^2a and R^2b is cyano and the other is an alkyl group optionally substituted by halo, a) by the reaction of a compound of the formula (III)

with an alkylating agent.

Suitable alkylating agents include alkyl halides, for example methyl iodide. The reaction is suitably carried out in the presence of a strong base such as butyllithium in an inert solvent, for example an ether such as tetrahydrofuran, at a non-extreme temperature, conveniently between -100 and 50ºC and suitably between -70º and 30°C.

The compounds of the formula (III) are suitably prepared by conversion of the corresponding compound containing an aldehyde function instead of a nitrile group. This conversion may be carried out by the reaction of the aldehyde with a suitable reagent such as O, N-bis (trifluoroacetyl)-hydroxylamine. This aldehyde is prepared in turn from the 2-unsubstituted dithiane or oxathiane by reaction with a formylating agent, such as dimethylformamide, in the presence of a strong base, for example butyllithium. b) by the reaction of a compound of the formula (IV) :

wherein R¹¹ is C_1-4 alkyl and R¹² is methyl optionally substituted b y halo, with a trialkylsilylcyanide in the presence of an acid catalyst. Suitably the alkyl groups in the trialkylsilylcyanide reagent contain 1 to 4 carbon atoms and are preferably methyl groups. Suitably the acid catalyst is a Lewis acid such as boron trifluoride etherate. The reaction is carried out in an inert solvent, such as a halogenated hydrocarbon, e.g. dichloromethane, at a non extreme temperature, for example between -50 and 80ºC, and conveniently between 0 and 30ºC.

The compounds of the formula (IV) may be prepared by the reaction of a compound of the formula (II) with the appropriate orthoester of the formula (V):

wherein R¹² and R¹³ are as hereinbefore defined. This reaction is conveniently carried out in the presence of an acid catalyst such as para toluene sulphonic acid, at an elevated temperature, i.e. between

50° and 180°C.

(iii) The compounds of the formula (I) wherein one or more of m and n is other than 0 may be prepared by oxidation of the corresponding compound of a lower oxidation state. The reaction is usually carried out in an inert solvent such as acetonitrile or a halogenated hydrocarbon such as chloroform at a non-extreme temperature, for example between 0 and 100 C and preferably between 20 and 30ºC. Suitable oxidising agents include peracids such as metachloro- perbenzoic acid. The oxidation is conveniently carried out in the presence of a buffer such as anhydrous sodium acetate. Compounds where m is 2 and n is 0 may be prepared from compounds of the formula (I) where m is 0 or 1, using potassium permanganate in a ketone, for example, acetone, at a non-extreme temperature for example -30ºC to 100 C and conveniently between -10º and 30ºC.

The compounds of formula (I) may be used to control pests such as arthropods, e.g. insect and acarine pests, helminths, e.g. nematodes and molluscs, e.g. slugs. Thus, the present invention provides a method for the control of arthropods, helminths and/or molluscs which comprises administering to the arthropod, helminth and/or mollusc or to their environment an effective amount of a compound of the formula (I). The present invention also provides a method for the control of arthropod, helminth and/or mollusc infestations of animals (including humans) and/or of plants (including trees) and/or stored products which comprises administering an effective amount of a compound of the formula (I). The present invention further provides for the compounds of the formula (I) for use in human and veterinary medicine, in public health control and in agriculture for the control of arthropod, helminth and/or mollusc pests.

By the term "control" is meant the amelioration of present or future deleterious effects of pests and includes killing adults, larvae and eggs, the inhibition of reproduction, the repellency and/or knockdown of pests, and any other influence on behaviour.

Compounds of formula (I) are of particular value in the protection of field, forage, plantation, glasshouse, orchard and vineyard crops, of ornamentals and of plantation and forest trees, for example, cereals (such as maize, wheat, rice, millet, oats, barley, sorghum), cotton, tobacco, vegetables and salads (such as beans, cole crops, cucurbits, lettuce, onions, tomatoes and peppers), field crops (such as potato, sugar beet, ground nuts, soyabean, oil seed rape), sugar cane, grassland and forage crops (such as lucerne), plantations (such as of tea, coffee, cocoa, banana, oil palm, coconut, rubber, spices), orchards and groves (such as of stone and pip fruit, citrus fruits, kiwifruit, avocado, mango, olives and walnuts), vineyards, ornamental plants, flowers and shrubs under glass and in gardens and parks, forest trees (both deciduous and evergreen) in forests, plantations and nurseries and plants grown for industrial or pharmaceutical purposes (such as the evening primrose).

They are also valuable in the protection of timber (standing, felled, converted, stored or structural) from attack by sawflies (e.g. Urocerus) or beetles (e.g. scolytids, platypodids, lyctids, bostrychids, cerambycids, anobiids).

They have applications in the protection of stored products such as grains, fruits, nuts, spices and tobacco, whether whole, milled or compounded into products, from moth, beetle and mite attack. Also protected are stored animal products such as skins, hair, wool and feathers in natural or converted form (e.g. as carpets or textiles) from moth and beetle attack; also stored meat and fish from beetle, mite and fly attack.

Compounds of formula (I) are of value in the control of public health pests, for example cockroaches and ants.

Compounds of formula I are also of value in the control of arthropods, helminths or molluscs which are injurious to, or spread or act as vectors of diseases in man and domestic animals, for example those hereinbefore mentioned, and more especially in the control of ticks, mites, lice, fleas, midges biting, nuisance and myiasis flies, mosquitos, hemiptrean bugs and snails.

The compounds of Formula (I) may be used for such purposes by application of the compounds themselves or in diluted form in known fashion as a dip, spray, fog, lacquer, foam, dust, powder, aqueous suspension, paste, gel, cream, shampoo, grease, combustible solid, vapourising mat, combustible coil, bait, dietary supplement, wettable powder, granule, aerosol, emulsifiable concentrate, oil suspension, oil solution, pressure-pack, impregnated article, microcapsule, pour on formulation or other standard formulations well known to those skilled in the art. Sprays may be applied by hand or by means of a spray race or arch or by vehicle or aircraft mounted apparatus. The animal, soil, plant or other surface being treated may be saturated with the spray by means of high volume application or superficially coated with the spray by means of light or ultra low volume application. Dip concentrates are not applied per se. but diluted with water and the animals immersed in a dipping bath containing the dip wash. Aqueous suspensions may be applied in the same manner as sprays or dips. Dusts may be distributed by means of a powder applicator or, in the case of animals, incorporated in perforated bags attached to trees or rubbing bars. Pastes, shampoos and greases may be applied manually or distributed over the surface of an inert material, such as that against which animals rub and transfer the material to their skins. Pour-on formulations are dispensed as a unit of liquid of small volume on to the backs of animals such that all or most of the liquid is retained on the animals.

Compounds of Formula (I) may be prepared either as formulations ready for use on the animals, plants or surface or as formulations requiring dilution prior to application, but both types of formulation comprise a compound of Formula (I) in intimate admixture with one or more carriers or diluents. The carriers may be liquid, solid or gaseous or comprise mixtures of such substances, and the compound of Formula (I) may be present in a concentration of from 0.025 to 99% w/v depending upon whether the formulation requires further dilution.

Dusts, powders and granules and other solid formulations comprise the compound of formula (I) in intimate admixture with a powdered solid inert carrier for example suitable clays, kaolin, bentonite, attapulgite, adsorbent carbon black, talc, mica, silica, chalk, gypsum, tricalcium phosphate, powdered cork, magnesium silicate, vegetable carriers, starch and diatomaceous earths. Such solid formulations are generally prepared by impregnating the solid diluents with solutions of the compound of formula (I) in volatile solvents, evaporating the solvents and, if desired, grinding the products so as to obtain powders and, if desired, granulating, compacting or encapsulating the products.

Sprays of a compound of Formula (I) may comprise a solution in an organic solvent (e.g. those listed below) or an emulsion in water (dip wash or spray wash) prepared in the field from an emulsifiable concentrate (otherwise known as a water miscible oil) which may also be used for dipping purposes. The concentrate preferably comprises a mixture of the active ingredient, with or without an organic solvent and one or more emulsifiers. Solvents may be present within wide limits but preferably in an amount of from 0 to 99.5% w/v of the composition and may be selected from kerosene, ketones, alcohols, xylene, aromatic naphtha, water, mineral oil, aromatic and aliphatic esters, and other solvents known in the formulating art. The concentration of emulsifiers may be varied within wide limits but is preferably in the range of 5 to 25% w/v and the emulsifiers are conveniently non-ionic surface active agents including polyoxyalkylene esters of alkyl phenols and polyoxyethylene derivatives of hexitol anhydrides and anionic surface active agents including Na lauryl sulphate, fatty alcohol ether sulphates, Na and Ca salts of alkyl aryl sulphonates and alkyl sulphosuccinates, soaps, lecithins, hydrolysed glues, etc.

Wettable powders comprise an inert solid carrier, one or more surface active agents, and optionally stabilisers and/or anti-oxidants.

Emulsifiable concentrates comprise emulsifying agents, and often an organic solvent, such as kerosene, ketones, alcohols, xylenes, aromatic naphtha, and other solvents known in the art.

Wettable powders and emulsifiable concentrates will normally contain from 0.5 to 99.5% by weight of the active ingredient, and are diluted, for example with water, before use. Lacquers comprise a solution of the active ingredient in an organic solvent, together with a resin, and optionally a plasticiser.

Dip washes may be prepared not only from emulsifiable concentrates but also from wettable powders, soap based dips and aqueous suspensions comprising a compound of Formula (I) in intimate admixture with a dispersing agent and one or more surface active agents.

Aqueous suspensions of a compound of Formula (I) may comprise a suspension in water together with suspending, stabilizing or other agents. The suspensions or solutions may be applied per se or in a diluted form in known fashion.

Greases (or ointments) may be prepared from vegetable oils, synthetic esters of fatty acids or wool fat together with an inert base such as soft paraffin. A compound of Formula (I) is preferably distributed uniformly through the mixture in solution or suspension. Greases may also be made from emulsifiable concentrates by diluting them with an ointment base.

Pastes and shampoos are also semi-solid preparations in which a compound of Formula (I) may be present as an uniform dispersion in a suitable base such as soft or liquid paraffin or made on a non-greasy basis with glycerin, mucilage or a suitable soap. As greases, shampoos and pastes are usually applied without further dilution they should contain the appropriate percentage of the compound of Formula (I) required for treatment.

Aerosol sprays may be prepared as a simple solution of the active ingredient in the aerosol propellant and co-solvent such as halogenated alkanes, propane, butane, dimethyl ether and the solvents referred to above, respectively. Pour-on formulations may be made as a solution or suspension of a compound of Formula (I) in a liquid medium. An avian or mammal host may also be protected against infestation of acarine ectoparasites by means of carrying a suitably-moulded, shaped plastics article impregnated with a compound of Formula (I). Such articles include impregnated collars, tags, bands, sheets and strips suitably attached to appropriate parts of the body. Suitably the plastics material is a polyvinyl chloride (PVC).

The concentration of the compound of formula (I) to be applied to an animal, premises, other substrates or outdoor areas will vary according to the compound chosen, the interval between treatments, the nature of the formulation and the likely infestation, but in general 0.001 to 20.0% w/v and preferably 0.01 to 10% of the compound should be present in the applied formulation. The amount of the compound deposited will vary according to the compound chosen, the method of application, area of application, concentration of the compound in the applied formulation, factor by which the formulation is diluted and the nature of the formulation.

Undiluted formulations such as pour-on formulations in general will be applied at a concentration in the range from 0.1 to 20.0% w/w and preferably 0.1 to 10%. The amount of compound to be applied to stored products in general will lie in the range of from 0.1 to 20ppm. Space sprays may be applied to give an average initial concentration of 0.001 to 1 mg of compound of formula (I) per cubic metre of treated space.

Compounds of formula (I) are of use in the protection and treatment of plant species, in which case an effective insecticidal, acaricidal, nematocidal or molluscicidal amount of the active ingredient is applied. The application rate will vary according to the compound chosen, the nature of the formulation, the mode of application, the plant species, the planting density and likely infestation and other like factors but in general, a suitable use rate for agricultural crops is in the range 0.001 to 3kg/Ha and preferably between 0.01 and lkg/Ha. Typical formulations for agricultural use contain between 0.0001% and 50% of a compound of formula (I) and conveniently between 0.1 and 15% by weight of a compound of the formula (I). Dusts, greases, pastes and aerosol formulations are usually applied in a random fashion as described above and concentrations of 0.001 to 20% w/v of a compound of Formula (I) in the applied formulation may be used.

The compounds of formula (I) have been found to have activity against the common housefly (Musca domestica). In addition, certain compounds of formula (I) have activity against other arthropod pests including Myzus persicae, Tetranychus urticae, Plutella xylostella, Culex spp. Tribolium castaneum, Sitophilus granarius, Periplaneta americana and Blattella germanica, The compounds of formula (I) are thus useful in the control of arthropods e.g. insects and acarines in any environment where these constitute pests, e.g. in agriculture, in animal husbandry, in public health control and in domestic situations.

Insect pests include members of the orders Coleoptera (e.g. Anobium,Ceutorhynchus,Rhynchophorus, Cosmopolites, Lissorhoptrus, Melipethes, Hypothenemus, Hylesinus, Acalymma, Lema, Psylliodes, Leptinotarsa, Gonocephalum, Agriotes, Dermolepida, Heteronychus, Phaedon, Tribolium, Sitophilus Diabrotica, Anthonomus or Anthrenus spp.), Lepidoptera (e.g. Ephestia, Mamestra, Earias, Pectinophora, Ostrinia, Trichoplusia, Pieris, Laphygma, Agrotis, Amathes, Wiseana. Tryporvza, Diatraea, Sporganothis, Cydia, Archios, Plutella, Chilo, Heliothis, Spodoptera or Tineola spp,), Diptera (e.g. Musca, Aedes, Anopheles, Culex, Glossina, Simulium, Stomoxys, Haematobia, Tabanus, Hydrotaea, Lucilia, Chrysomia, Callitroga, Dermatobia, Gasterophilus, Hvpoderma, Hylemyia, Atherigona, Chlorops, Phvtomvza, Ceratitis, Liriomyza and Melophagus spp.), Phthiraptera (Malophaga e.g. Damalina spp. and Anoplura e.g. Linognathus and Haematopinus spp.), Hemiptera (e.g. Aphis , Bemisia,Phorodon, Aeneolamia, Empoasca, Parkinsiella, Pyrilla, Aonidiella, Coccus, Pseudococcus, Helopeltis, Lygus, Dysdercus, Oxycarenus, Nezara, Aleurodes, Triatoma, Rhodnius, Psylla, Myzus, Megoura, Phylloxera, Adelves, Niloparvata, Nephrotettix or Cimex spp,), Orthoptera (e.g. Locusta, Gryllus, Schistocerca or Acheta spp,), Dictyoptera (e.g. Blattella, Periplaneta or Blatta spp.), Hymenoptera (e.g. Athalia. Cephus, Atta Lasius. Solenopsis or Monomorium spp.), Isoptera (e.g. Odontotermes and Reticulitermes spp.), Siphonaptera (e.g. Ctenocephalides or Pulex spp.), Thysanura (e.g. Lepisma spp.), Dermaptera (e.g. Forficula spp.), Psocoptera (e.g. Peripsocus spp.) and Thysanoptera (e.g. Thrips tabaci),.

Acarine pests include ticks, e.g. members of the genera Boophilus,Ornithodorus, Rhipicephalus, Amblyomma, Hyalomma. Ixodes, Haemaphysalis, Dermacentor and Anocentor, and mites and manges such as Acarus, Tetranychus, Psoroptes, Notoednes, Sarcoptes. Psorergates, Chorioptes, Eutrombicula. Demodex, Panonychus, Bryobia and Eriophyes spp.

Nematodes which attack plants and trees of importance to agriculture, forestry, horticulture, either directly or by spreading bacterial, viral, mycoplasma or fungal diseases of the plants, include root-knot nematodes such as Meloidogyne spp. (e.g. M. incognita) : cyst nematodes such as Globodera spp. (e.g. G. rostochiensis): Heterodera spp. (e.g. H. avenae); Radopholus spp. (e.g. R. similis); lesion nematodes such as Pratylenchus spp. (e.g. P. pratensis); Belonolaimus spp. (e.g. B. gracilis); Tylenchulus spp. (e.g. T. semipenetrans); Rotylenchulus spp. (e.g.R. reniformis); Rotylenchus spp. (e.g. R. robustus); Helicotylenchus spp. (e.g. H. multicinctus); Hemicvc1iophora spp. (e.g. H. gracilis): Criconemoides spp. (e.g. C. similis); Trichodorus spp. (e.g. T primitivus); dagger nematodes such as Xiphinema spp. (e.g. X. diversicaudatum), Longidorus spp (e.g. L. elongatus): Hoplolaimus spp. (e.g. H. coronatus); Aphelenchoides spp. (e.g. A. ritzema-bosi. A. besseyi): stem and bulb eelworms such as Ditylenchus spp. (e.g. D. dipsaci).

Mollusc pests which attack plants and trees of importance to agriculture, foresty and horticulture include slugs such as Deroceras spp. (e.g. P. reticulatum - the grey field slug); the Arion group; Milax spp; land snails such as Helix spp. and aquatic snails such as Planorbis spp. Mollusc pests which act as vectors of diseases in man and domestic animals include Bulinus spp., Physopsis spp., Planorbis spp. and Oricomelania spp.

Compounds of the invention may be combined with one or more other pesticidally active ingredients (for example pyrethroids, carbamates lipid amides and organophosphates) and/or with attractants, repellents, bacteriocides, fungicides, anthelmintics and the like. Furthermore, the activity of compounds of the invention may be enhanced by the addition of a synergist or potentiator, for example: one of the oxidase inhibitor class of synergists, such as piperonyl butoxide, propyl 2-propynylphenyl- phosphonate; a second compound of the invention; or a pyrethroid pesticidal compound. When an oxidase inhibitor synergist is present in a formulation of the invention, the ratio of synergist to compound of Formula (I) will be in the range 500:1-1:25 eg about 100:1 to 10:1.

Stabilisers for preventing any chemical degradation which may occur with the compounds of the invention include, for example, antioxidants (such as tocopherols, butylhydroxyanisole and butylhydroxytoluene) and scavengers (such as epichlorhydrin) and organic or inorganic bases e.g. trialkylamines such as triethylamine which can act as basic stabilisers and as scavengers.

The following examples serve to illustrate the preparation and properties of compounds of the present invention.

Example 1.

5(e)-t-Butyl-2(e)-methyl,1,3-dithiaπe-2(a)-carbonitrile i) A solution of n-butyllithium in hexane (1.6M; 17.75mls) was added to a stirred solution of 5-t-butyl-1,3-dithiane (5g) (E.L. Eliel et al. J.Amer.Chem.Soc. 1976, 98(12),3583) in tetrahydrofuran (50mls) at -30º under a nitrogen atmosphere. After 1 hour of additional stirring, the mixture was transferred by syringe and added, dropwise, to neat dimethylformamide (10mls) cooled to -10 . The mixture was stirred for 1 hour at -10 and then stored overnight at 0ºC. The reaction mixture was then poured into ice-water (100mls) and extracted with hexane. The aqueous layer was neutralised with dilute hydrochloric acid and then re-extracted with diethyl ether. The ethereal extracts were dried over anhydrous magnesium sulphate and the evaporated in vacuo to leave a white solid residue (3.1g). 5-t-Butyl-2-formyl- 1,3-dithiane, thus obtained, is present to a large extent as a dimer. ii) 5-t-Butyl-2-formyl-1,3-dithiane (1g) was heated to melting, under a nitrogen atmosphere, and then allowed to cool. The viscous oil thus obtained was taken up in dry benzene (100mls) containing pyridine (0.78g). O,N-Bis-(trifluoroacetyl)-hydroxylamine (1.1g) (J.H. Pomeroyn et al, J.Amer.Chem.Soc. 1959, 81 6340) was added and the resulting mixture was heated to reflux for two hours. After cooling, ether and water were added and the organic layer separated. The aqueous layer was further extracted with fresh ether and the combined organic extracts were dried over anhydrous magnesium sulphate and then evaporated in vacuo to leave a yellow solid, which was purified by column chromatography on silica. Gradient elution with hexane/dichloromethane mixtures gave 5-t:-butyl-1-cyano-1,3-dithiane as a white solid (0.38g). iii) A solution of 5-t-butyl-2-cyano-1,3-dithiane (0.2g) in tetrahydrofuran (10ml) was cooled to -40 under a nitrogen atmosphere. A solution of n-butyllithium in hexane (1.6M.0.7mls) was added and the resulting mixture maintained at -40 for 1.5 hours when methyl iodide (0.2ml) was added. The reaction mixture was allowed to warm to room temperature overnight. After this time, diethyl ether and water were added. The organic phase was separated and the aqueous layer extracted with fresh ether. The combined organic extracts were dried over anhydrous magnesium sulphate and evaporated in vacuo. The residue was purified by column chromatograph on alumina, eluting with hexane/ether (1:9), to give 5(e)-t-butyl-2(e)-methyl-1,3-dithiane-2(a)carbonitrile as a white solid (100mg) after recrystallisation from hexane.

Example 2.

5(e)-t-Butyl-2(a)-methyl-1,3-dithiane-2(e)-carbonitrile i) Boron trifluoride etherate (2.15mls) was added to a stirred solution of 2-t-butylpropane-1,3-dithiol (4.4g) (European patent application 294228) and acetaldehyde (1.5mls) in dry chloroform under nitrogen. The resulting mixture was stirred at room temperature overnight. After this time, the mixture was washed with water, saturated sodium bicarbonate and brine before drying over anhydrous magnesium sulphate and evaporation in vacuo. 5-t-Butyl-2-methyl-1,3-dithiane (4.7g) was obtained as a pale yellow oil which solidified on cooling. ii) Using the methods described in Example 1 stages (i) and (ii), 5-t-butyl-2-methyl-1,3-dithiane was converted to 5(e)-t-butyl- 2(a)-methyl-1,3-dithiane-2(e)-carbonitrile.

Example 3.

5(e)-t-Butyl-2,2-dimethyl-1,3-dithiane

Using the method described in Example 2 stage (i), 5(e)-t:-butyl-2,2-dimethyl-1,3-dithiane was prepared from acetone and 2-t:-butylpropane-1,3-dithiol. The crude product was purified by chromatography on silica, eluting with hexane/dichloromethane (9:1) followed by recrystallisation from chloroform/methanol. cis/trans-5(e)-t-Butyl-2-methyl-2-trifluoromethyl-1,3-dithiane was prepared in an analogous manner starting from 1,1,1-trifluoroacetone and 2-t-butylpropane-1,3-dithiol. Example 4.

2(e)-Methyl-5(e)-(2,2,2-trifluoro-1-methylethyl)-1,3-dithiane-2(a)-carbonitrile i) A mixture of 2-(2,2,2-trifluoro-1-methylethyl)-propan,1,3-dithiol (4.8g) (European patent 0372816A) and dimethoxymethane (2.1ml) in dry chloroform (15ml) was added to a refluxing solution of boron trifluoride etherate (2.9ml) and glacial acetic acid (10ml) in chloroform (50ml) under a nitrogen atmosphere. The addition took place over one hour and the resulting mixture was then refluxed for a further two hours and then stirred at room temperature overnight. After this time the reaction mixture was washed with water, saturated sodium bicarbonate and brine before drying over anhydrous magnesium sulphate and evaporation in vacuo. 5-(2,2,2- trifluoro-1-methylethyl)-1,3-dithiane (3.6g), thus obtained, was used without further purification. ii) Using the methods described in Example 1, 5-(2,2,2-trifluoro-1- methylethyl)-1,3-dithiane was converted to 2(e)-Methyl-5(e)- (2,2,2-trifluoro-1-methylethyl)-1,3-dithiane-2(a)-carbonitrile.

In a similar manner and starting from 2-(1,1-dimethyl-2,2,2-tri¬fluoroethyl)-propan-1,3-dithiol (EP 0372816A) was prepared 5(e)-(1,1-dimethyl-2,2,2-trifluoroethyl)-2(e)-methyl-1,3-dithiane-2(a)-carbonitrile. In a similar manner and starting from 2-cyclopropyl-propan-1,3-dithiol (EP 0372816A) was prepared 5(e)-cyclopropyl-2(e)-methyl-1,3-dithiane-2(a)-carbonitrile.

Example 5.

5(e)-t-Butyl-2(e)-methyl-1,3-oxathiane-2(a)-carbonitrile i) A mixture of 2-t-butylpropane-1,3-diol (11.0g.) (E.L. Eliel et al J. Amer Chem Soc. 1968, 90, 3444) in dry toluene (200ml), was stirred at 20ºC. Sodium hydride (2.4g., 80% dispersion in oil), previously washed with hexane, was added carefully to the stirred mixture. The mixture was stirred at 120°C for 30 minutes and cooled. Benzyl bromide (9.5ml) was added dropwise and the mixture heated at 130°, with stirring for 6 hours. The mixture was cooled, water was added and the mixture extracted with diethyl ether. The ethereal extracts were washed with water, dried over anhydrous magnesium sulphate and evaporated in vacuo. The residue was purified by chromatography on silica, eluting with 1:4 diethyl ether: hexane. 2-Benzyloxymethyl-3,3-dimethyl- butan-1-ol (8.0g) was obtained as a colourless oil. ii) 2-Benzyloxymethyl-3,3-dimethylbutan-1-ol (5.8g) in dry pyridine (20ml) was stirred at 0ºC. Then methanesulphonyl chloride (3.5g) was added dropwise and the mixture was stirred at 0ºC for 3 hours and at 20°C for 5 hours. Water was added and the aqueous mixture was extracted with diethyl ether. The ethereal extracts were washed with water, dried over anhydrous magnesium sulphate and evaporated in vacuo.

2-Benzyloxymethyl-3,3-dimethyIbut-1-yl methanesulphonate was obtained as a yellow oil (7.3g) and was used without further purification. iii) Benzyl mercaptan (3.1ml) was stirred in dry dimethylformamide (100ml), at 0º, under a current of nitrogen. Sodium hydride (0.75g., 80% dispersion in oil), previously washed with hexane, was added carefully and the mixture was stirred at 0ºC for 30 minutes. 2-Benzyloxymethyl-3,3-dimethylbut-1-yl methanesulphonate (7.3g), in dry dimethylformamide (20ml) was added and the mixture was stirred at 100° for 3 hours. The mixture was cooled and water was added. The aqueous mixture was extracted with diethyl ether. The ethereal extracts were washed with water, dried over anhydrous magnesium sulphate and evaporated in vacuo. The residue was purified by chromatography on silica, eluting with 1:4 diethyl ether: hexane. 2-Benzylthiomethyl-3,3-dimethylbutyl benzyl ether was obtained as a colourless oil (7.0g). iv) Anhydrous liquid ammonia (400ml) was stirred at -70º, under a current of nitrogen. 2-Benzylthiomethyl-3,3-dimethylbutyl benzyl ether (7.0g) in dry diethyl ether (100ml) was added and this was followed by sodium (4.0g) in small pieces. The resulting mixture was stirred at -70° for 3 hours and then allowed to warm up to 20ºC. Ammonium chloride (20g) was added followed by dry methanol (70ml). When all the sodium had dissolved, water was added and the mixture was extracted with diethyl ether. The ethereal extracts were washed with water, dried over anhydrous magnesium sulphate and evaporated in vacuo. 3,3-Dimethyl-2-mercaptomethylbutan-1-ol was obtained as a pale yellow oil (2.8g) and was used without further purification. v) A mixture of 3,3-dimethyl-2-mercaptomethylbutan-1-ol (1.66g), triethyl orthoacetate (1.82g) and p-toluenesulphonic acid (catalytic quantity) was heated under a stream of nitrogen until no further ethanol was evolved. The resultant brown oil was purified by chromatography on alumina, eluting with 4% dichloro- methane (saturated with ammonia) in hexane. 5-t-Butyl-2-(a)-ethoxy-2(e)-methyl-1,3-oxathiane (1.0g) was obtained as a pale yellow oil. vi) Trimethylsilyl cyanide (0.37g) was added to a solution of 5-t-butyl-2(a)-ethoxy-2(e)-methyl-1,3-oxathiane (0.78g) in dichloromethane (10ml) at 0ºC under nitrogen, followed by boron trifluoride etherate (0.025g), in a dropwise manner, and the solution allowed to warm to room temperature overnight. The yellow solution was diluted with ether, washed with sodium bicarbonate solution, brine, dried over sodium sulphate and evaporated in vacuo. The residue was purified by chromatography on alumina eluting with 2% ether: hexane. 5(e)-t-Butyl-2(e)- methyl-1,3-oxathiane-2(a) carbonitrile (0.51g) was obtained as a pale yellow oil.

Example 6.

5(e)-t-Butyl-2(e)-methyl-1,3-dithiane-2(a)-carbonitrile-1(e)-oxide i) m-Chloroperoxybenzoic acid (85%, 0.19g) was added to a stirred solution of 5(e)-t-butyl-2(e)-methyl-1,3-dithiane-2(a)-carbonitrile (0.2g) in dry acetonitrile (30ml) containing sodium acetate (0.5g). The resulting mixture was stirred for two hours at room temperature . After this time, insoluble material was removed by filtration and washed with ethyl acetate. The resulting filtrate was dried over magnesium sulphate and evaporated in vacuo. The residue was purified by column chromatography on silica. Gradient elution with hexane/ethyl acetate mixtures gave 5(e)-t-bu- tyl-2(e)-methyl-1,3-dithiane-2-(a)-carbonitrile 1(e)-oxide as a white solid (0.17g).

In a similar manner, and starting from 5(e)-t-butyl-2(e)-methyl- 1,3-oxathiane-2(a)-carbonitrile, was prepared 5(e)-t-butyl-2(e)- methyl-1,3-oxathiane-2(a)-carbonitrile 3(a)-oxide and 5(e)-t-butyl-2(e)-methyl-1,3-oxathiane-2(a)-carbonitrile 3(e)-oxide.

Example 7.

5(e)-t-Butyl-2(e)-methyl-1,3-dithiane-2(a)-carbonitrile 1,1-dioxide

Potassium permanganate (0.36g) was added to a stirred mixture of 5(e)-t-butyl-2(e)-methyl-1,3-dithiane-2(a)-carbonitrile 1(e)-oxide (0.35g) and magnesium sulphate (Ig) in acetone (15ml). The resulting mixture was maintained at room temperature for 4 hours and then filtered through Celite. The colourless filtrate was evaporated in vacuo to leave 5 (e) - t-butyl-2 (e) -methyl- 1 , 3-dithiane- 2 (a) -carbonitrile 1 , 1-dioxide as a white solid (0. 33g) .

Example 8.

5 (e)-t-Butyl-2(e)-methyl-1,3-oxathiane-2(a)-carbonitrile 3,3-dioxide

A mixture of 5(e)-t-butyl-2(e)-methyl-1,3-oxathiane-2-(a)-carbonitrile (100mg), and magnesium monoperoxyphthalate (0.28g) in ethanol: water (20:10ml) were heated at reflux for 2 hours. Ethanol was removed under reduced pressure, the product extracted with ether, washed with brine, dried over magnesium sulphate and the solvent removed in vacuo . The residue was purified by column chromatography on silica, eluting with ether hexane (1:4). 5(e)-t-Butyl-2(e)-methyl-1,3-oxathiane-2(a)-carbonitrile 3,3-dioxide (37mg) was obtained as a white solid.

Formulations

1. Emulsifiable Concentrate

Compound of formula (I) 10.00

Alkyl phenol ethoxylate* 7.50

Alkyl aryl sulphonate* 2.50

C_{8 - 13} aromatic solvent 80.00

100.00

2. Emulsifiable Concentrate

Compound of formula (I) 10.00

Alkyl phenol ethoxylate* 2.50

Alkyl aryl sulphonate* 2.50

Ketonic solvent 64.00

C_{8 - 13} aromatic solvent 18.00

Antioxidant 3.00

100.00 3. Wettable Powder

Compound of formula (I) 5 .00

C_{8 - 13} aromatic solvent 7 .00

C₁₈ aromatic solvent 28 .00

China clay 10 .00

Alkyl aryl sulphonate* 1. 00 Napthalene sulphonic acid* 3. 00 Diatomaceous earth 46. 00

100. 00

Dust

Compound of formula (I) 0.50 Talc 99.50

100.00

Bait

Compound of formula (I) 0.50

Sugar 79.50

Paraffin wax 20.00

100.00

Emulsion Concentrate

Compound of formula (I) 5 .00

C_{8 - 13} aromatic solvent 32 .00

Cetyl alcohol 3 .00

Polyoxyethylene glycerol monooleate* 0 .75

Polyoxyethylene sorbitan esters* 0 .25

Silicone solution 0. 10

Water 58. 99

100.00 7. Suspension Concentrate

Compound of formula (I) 10.00 Alkyl aryl ethoxylate* 3.00 Silicone solution 0.10 Alkane diol 5.00 Fumed silica 0.50 Xanthan gum 0.20 Water 80.00 Buffering agent 1.20

100.00

Microemulsion

Compound of formula (I) 10.00 Polyoxyethylene glycerol monooleate* 10.00 Alkane diol 4.00 Water 76.00

100.00

Water Dispersible Granules

Compound of formula (I) 70 .00 Polyvinyl pyrrolidine 2.50 Alkyl aryl ethoxylate 1 .25 Alkyl aryl sulphonate 1.25 China clay 25 .00

100.00 10. Granules

Compound of formula (I) 2 .00 Alkyl phenol ethoxylate* 5 .00 Alkyl aryl sulphonate* 3 .00

C_{8 - 13} aromatic solvent 20 .00 Kieselguhr granules 70 .00

100. 00

11. Aerosol (pressure pack)

Compound of formula (I) 0.30

Piperonyl butoxide 1.50

C_{8 - 13} saturated hydrocarbon solvent 58.20

Butane 40.00

100.00

12. Aerosol (pressure pack)

Compound of formula (I) 0.30

C_{8 - 13} saturated hydrocarbon solvent 10.00

Sorbitan monooleate* 1.00

Water 40.00

Butane 48.70

100.00

13. Aerosol (pressure pack)

Compound of formula (I) 1.00

CO₂ 3.00

Polyoxyethylene glycerol monooleate* 1.40

Propanone 38.00

Water 56.60

100.00 14. Lacquer

Compound of formula (I) 2.50

Resin 5.00

Antioxidant 0.50

High aromatic white spirit 92.00

100.00

15. Spray (ready to use)

Compound of formula (I) 0 .10 Antioxidant 0 .10 Odourless kerosene 99.80

100.00

16. Potentiated Spray (ready to use)

Compound of formula (I) 0.10 Piperonyl butoxide 0 .50 Antioxidant 0 .10 Odourless kerosene 99 .30

100.00

17. Microencapsulated

Compound of formula (I) 10.00

C_{8 - 13} aromatic solvent 10.00

Aromatic di-isocyanate# 4.50

Alkyl phenol ethoxylate* 6.00

Alkyl diamine# 1.00

Diethylene triamine 1.00

Concentrated hydrochloric acid 2.20

Xanthan gum 0.20

Fumed silica 0.50

Water 64.60

100.00 * = Surfactant

= = react to form the polyurea walls of the microcapsule

Antioxidant could be any of the following individually or combined

Butylated hydroxytoluene

Butylated hydroxyanisole

Vitamin C (ascrobic acid)

BIOLOGICAL ACTIVITY

The following examples illustrate in a non-limiting manner the pesticidal activity of compounds of formula I.

Spray Tests

The activity of the compounds of the invention was demonstrated by dissolving the compounds in acetone (5%) and then diluting in water: "Synperonic" (94.5%: 0.5%) to give an aqueous emulsion. This was used to treat the following insects.

Musca domestica

20 Female Musca were contained in a cardboard cylinder with gauze over either end. Solution of the compound was sprayed onto the insects so enclosed and mortality assessed after 48 hours at 25°C.

The following compounds were active at less than 1000p.p.m.:-

6, 12, 13.

Plutella xyostella

10 Plutella larvae were put onto leaf discs and sprayed with the solution of the compound. Mortality was assessed after 2 days at 25°C. The following compounds were active at less than 1000p . p . m. : -

1. 2 , 3 , 5 .

Myzus persicae

10 Adults were placed on a leaf disc of Chinese cabbage. 24 Hours later the disc was sprayed with the solution of compound. Mortality was assessed after 2 days at 25°C.

The following compounds were active at less than 1000p.p.m.:-

11, 12, 13.

The following compounds were active at less than 200p.p.m.:-

3, 7, 10.

Diabrotica undecimpunctata

Filter paper and food were sprayed with a solution of the compound. Subsequently, the filter paper was infested with 10 second instar larvae. Mortality was assessed after 48 hours.

The following compounds were active at less than 1000p.p.m.:-

The following compounds were active at less than 200p.p.m. 1, 2, 3, 5, 11, 6, 7, 9, 8, 10, 12, 13. TABLE 1.

Compound Isomer Number R^5eq. R^5ax R^2eq. R^2ax Ratio

1. S ^tBu H Me CN

2. S ^tBu H CN Me

3. S ^tBu H Me Me

4. S ^tBu H Me CF₃) - tBu H CF₃ Me ) 1:1

5. S 2,2,2-trifluoro-1- H Me CN

methylethyl

6. S 1,1-dimethyl-2,2,2- H Me CN

trifluoroethyl

7. S cycloproplyl H Me CN

8. O ^tBu H Me CN

TABLE 2.

Compound

Number R 5eq. R 5ax m m

9. S ^tBu H 0 1 10. S ^tBu H 1 1 11. O ^tBu H 0 1 12. O H 1 0 13. O ^tBu H 1 1

TABLE 3

Nuclear Magnetic Resonance Spectra: H, CDCl₃, expressed as ppm downfield from TMS.

(number of protons, multiplicity, J_Hz).

Compound

Number

1. 0.95(9H,S), 1.60(1H,tt), 1.82(3H,s), 2.90(2H,m), 3.05(2H,m)

2. 1.0(9H,S) , 1.93(3H,s) 1.96(lH,m), 2.90(2H,m), 3.08(2H,m).

3. 0.95(9H,S) , 1.55(3H,s , 1.61(lH,m) , 1.82(3H,s), 2.70(2H,m), 2.86(2H,m).

4. 0.93 (9H,s, one isomer) 1.02 (9H,s, other isomer), 1.53-1.80(4H,m) , 2.65,2.9-3.15(4H,m

5. 1.22(3H,d) , 1.86(3H,s , 2.35(2H,m) , 2.80(2H,m), 3.25(2H,m).

6. 1.20(6H,S), 1.85(3H,S , 2.15(lH,m), 2.96(2H,m), 3.20(2H,m).

7. 0.25(2H,m), 0.60(3H,m , 0.95(lH,m), 1.85(3H,s), 2.94(2H,m), 3.16(2H,m).

8. 0.90(9H,S), 1.70(1H,m , 1.80(3H,s), 2.81(1H,dt), 3.10(1H,dd), 3.84(1H,t), 4.17(1H,

9. 0.98(9H,S) , 1.95(3H,S , 2.15(lH,m) , 2.70(1H,m), 2.86 (2H,m), 3.44(1H,m).

10. 1.00(9H,s), 1.89(3H,s , 2.46(lH,m), 2.88(lH,m), 3.06(1H,dd), 3.33(2H,m).

11. 1.00(9H,s) , 1.87(1H,m , 1.95(3H,s) , 2.90(1H,t), 3.54(1H,dt), 3.84(1H,t), 4.10(1H,m) 12. 0.95(9H,s), 1.80(3H,s , 2.31(lH,m), 2.97(1H,dd), 3.30(1H,dt), 3.90(1H,t), 4.23(1H, 13. 1.00(9H,S), 1.85(3H,S , 2.36(lH,m), 3.30(2H,m), 3.98(1H,dd), 4.25(1H,m).

TABLE 4

Further Characterising Data

Compound Mass Spectrum

Number Chemical Ionisation M.p. Description Method of

(M + 1) Synthesis

1. 216 140° White Solid Example 1.

2. 216 71° White Solid Example 2.

3. 205 94° White Solid Example 3.

4. 259 153-9º White Solid Example 3.

5. 256 73° White Solid Example 4.

6. 270 104° White Solid Example 4.

7. 200 64º White Solid Example 4.

8. 200 Oil Example 5.

9. 232 121º White Solid Example 6. 10. 248 152º White Solid Example 7. 11. 216 111º White Solid Example 6. 12. 216 50º White Solid Example 6. 13. 232 115º White Solid Example 8.

Claims

CLAIMS 1. A method for controlling pests which comprises contacting the pest with a pesticidally effective amount of a compound of the formula (I):

which contains between 8 and 30 carbon atoms , and wherein Y is oxygen or a group S(O)_m and m and n are independently selected from 0, 1 and 2; R^2a and R² are the same or different and each is selected from cyano, nitro, methyl optionally substituted by halo, a group S(O)_qR⁷ where q is 0, 1 or 2 and R⁷ is methyl or ethyl, or a group COR⁸ where R⁸ is hydrogen, hydroxy, C_1-4 alkoxy, C_1-4 alkyl optionally substituted by fluoro or a group

NR⁹R¹⁰ wherein R⁹ and R¹⁰ are independently selected from hydrogen, methyl or ethyl; R^4a and R^4b, R^6a and R^6b are independently selected from hydrogen, methyl, cyano or trifluoromethyl, R^5a is a primary, secondary or tertiary C_2-5 alkyl group optionally substituted by halo or C. , alkoxy, or a C_3-4 cycloalkyl group, or R^5a is a C_3-4 cycloalkyl group and R^5a is hydrogen, hydroxy, C_1-4 alkoxy, C_1-4 alkanoyloxy, or C_1-4 alkyl optionally substituted by alkoxy; or R^5a and R^5b form a gem di-methyl group or are linked together with the ring carbon to which they are attached to form a 3- to 5-membered ring that optionally contains a hetro atom or an olefinic bond and is optionally substituted by a C_1-4 alkyl group optionally substituted by halo.
2. A method according to claim 1 wherein Y is oxygen or sulphur.
3. A method according to claim 1 or 2 wherein R^2a and R^2b are the same or different and each is selected from methyl, ethyl, cyano or trifluoromethyl.
4. A method according to claim 3 wherein R^2a is methyl.
5. A method according to claim 3 wherein R^2b is methyl or cyano.
6. A method according to any of claims 1 to 5 wherein R^4a, R^4b, R^6a and R^6b are each selected from hydrogen, or methyl.
7. A method according to any of claims 1 to 6 wherein R^5a is a secondary or tertiary C_2-5 alkyl group optionally substituted by fluoro or a cyclopropyl group.
8. A method according to any of claims 1 to 7 wherein R^5b is hydrogen, methyl or ethyl.
A compound of the formula

wherein Y, R^2a, R^4a, R^4b, R^5b, R^6b, m and n are as defined m claim 1 and R is cyano, nitro, a group S(O)_qR⁷, a group COR⁸ wherein a R⁷ and R⁸ are as defined in claim 1, or a C_1-3 alkyl group substituted by halo.
10. A compound selected from:-

5(e)-t-Butyl-2(e)-methyl-1,3-dithiane-2(a)-carbonitrile

5(e)-t:-Butyl-2(a)-methyl-1,3-dithiane-2(e)-carbonitrile

5(e)-t-Butyl-2(e)-methyl-1,3-dithiane-2(a)-carbonitrile-1(e)- oxide

5(e)-t-Butyl-2(e)-methyl-1,3-dithiane-2(a)-carbonitrile-1,1- dioxide

2(e)-Methyl-5(e)-(1-methyl-2,2,2-trifluoroethyl)-1,3-dithiane- 2(a)-carbonitrile

5(e)-Cyclopropyl-2(e)-methyl-1,3-dithiane-2(a)-carbonitrile

5(e)-t-Butyl-2(e)-methyl-1,3-oxathiane-2(a)-carbonitrile

5(e)-t-Butyl-2(e)-methyl-1,3-oxathiane-2(a)-carbonitrile-3(a)- oxide

5(e)-t-Butyl-2(e)-methyl-1,3-oxathiane-2(a)-carbonitrile-3(e)- oxide

5(e)-t-Butyl-2(e)-methyl-1,3-oxathiane-2(a)-carbonitrile-3,3- dioxide
11. A process for the preparation of a compound of the formula (I)

which process comprises: (i) the reaction of a compound of the formula (II)

wherein X is SH and Y is SH or OH with a suitable aldehyde or ketone of the formula or a reactive derivative thereof, wherein the R substituents at the 2,4,5 and 6 positions are as defined in claim 1 or claim 12 and, optionally, thereafter oxidising one or two ring sulphur atoms, or

(ii) when one of R^2a and R^2b is cyano and the other is an alkyl group optionally substituted by halo: a) the reaction of a compound of the formula (III)

with an alkylating agent, or b) the reaction of a compound of the formula (IV)

wherein R¹¹ is C_1-4 alkyl and R¹² is methyl optionally substituted by halo with a triakylsilylcyanide in the presence of an acid catalyst.
12. A method for the control of pest infestation of plants and/or stored products and/or an environment which comprises administering an effective amount of a compound of the formula (I) as defined according to any one of claims 1 to 9 to the plant and/or stored product and/or environment susceptible to pest infestation.
13. A method for the control of pest infestations on animals which comprises administering to the animal an effective amount of a compound of the formula (I) as defined according to any one of claims 1 to 9.
14. A pesticidal formulation comprising a compound of the formula (I) as defined in any one claims 1 to 9 in admixture with one or more carriers or diluents.
15. A pesticidal formulation according to claim 14 which additionally contains a synergist or potentiator.
16. A pesticidal formulation according to either claim 14 or claim 15 which additionally contains one or more pesticidally active ingredients, attractants, repellents, bacteriocides, fungicides and/or anthelmintics.