IE41614B1 - Substituted 2,2-dimethyl cylopropane carboxylic acid estersprocess for their preperation and their use as insecticides - Google Patents

Abstract

Insecticides of formula: have particularly good kill and/or knock down properties when R2 and R4 are fluorine, chlorine or bromine and R is 3-phenoxybenzyl or .alpha.-cyano-3-phenoxybenzyl or when at least one of R2 and R3 is fluorine, R can also be 5-benzyl-3-furylmethyl and the ester is in the form of a substantially pure optical isomer with respect to the cyclopropane ring and has ¢R! configuration at C1 of the cyclopropane ring. The esters may be prepared by conventional esterification or by a Wittig synethesis using the desired ester of caronaldehyde and a phosphorane derived from the appropriate dihalo compound. The resolution about the cyclopropane ring can be before or after the esterification or Wittig reaction. The crystalline isomer of the compound wherein R2 and R3 are each bromine and R is .alpha.-cyano-3-phenoxybenzyl has a relative toxicity to houseflies about 23 times greater than that of 5-benzyl-3-furylmethyl (+)-trans chrysanthemate.

Description

This invention relates to insecticides and more particularly, to synthetic insecticides of the pyrethrin type, to their preparation, to compositions containing them and to the insecticidal use of the compounds and compositions.

In Patent Specification No. 37681 we have described and claimed esters of the general formula: ΙΟ 2. ' R (R )C = C CH -CH - COOR CHg CHg II 2 wherein R represents hydrogen or a methyl group; R represents hydrogen or a halogeno or alkyl group; R represents hydrogen or a halogeno or carboalkoxy group , said carboalkoxy group containing at least 2 carbon 2 atoms in the alkoxy residue when R represents methyl; 3 with the proviso that (a) R and R each represent hydrogen only when R^ represents methyl, (b) when R^ 3 and R each represent hydrogen and R represents alkyl, that alkyl group contains at least two carbon 3 atoms and (c) when R represents an alkyl group, R does not represent a halogeno group and ft represents a group of formula: - 2 41614 wherein Z represents 0, S, CH2 or CO, Y represents hydrogen or an alkyl, alkenyl or alkynyl group or an aryl or furyl group which is unsubstituted or substituted in the ring by one or more alkyl, Θ alkenyl, alkoxy or halogeno groups, R and R , which may be the same or different, each represent g hydrogen or an alkyl, or alkenyl group, R represents hydrogen or a methyl group, R^ and R3-3·, which may be the same or different, each represent hydrogen or an 12 alkyl group, R represents an organic radical having carbon-carbon unsaturation in a position « to the 12 CH2 group to which R is attached. @ indicates an aromatic ring or a dihydro or tetrahydro analogue thereof, X1, X2, X3 and X4, which may be the same or different, each represent hydrogen, chlorine or a methyl group, Z represents -CH2~ or -0- or -S- or -CO-, D _ 1 2 represents H, CN or -C.=ECH, Z and Ζ , which may be the same or different, each represent chlorine or a methyl group and n=0, 1 or 2, or when R represents a halogeno group, or when R represents an alkyl group and R3 represents hydrogen, subject to proviso (b) above, R may also represent hydrogen (or a salt . or acid halide derivative of the acid) or an alkyl group, with the proviso that R does not represent hydrogen (or an acid chloride derivative of the acid) or an ethyl or allethronyl group when R3- represents hydrogen, 3 R and R each represent chlorine and the compound is racemic.

We now find that substantially pure optical - 4 41614 i;!i>nn'i ot certain esti'is of formula II in which 2 3 R repiesents hydrogen and R and R each represents a halogen which is fluorine, chlorine or bromine, have particularly potent insecticidal and/οχ knock down propert ies.

Accordingly, the present invention provides a cyclopropane carboxylic acid ester of the general formula: CH CH -CH - COOR CH3 ch3 IIA wherein the compound is in the form of a substantially pur·' optical isomer with respect to the cyclopropane ιing and having the [R] configuration at the carbon atom 2 of the cyclopropane ring carrying the COOR group and R and R1, which may be the same or different, each represent fluorine, chlorine or bromine and R represents 3-phenoxybenzyl or a-cyano-3-phenoxbenzyl or, when at 3 2 least one of R and R represents fluorine, or when R and R each represent chlorine and the cyclopropane ring has the [iR.cis] configuration, R may also represent 5-benzyl-3-furylmethyl.

Our biological investigations indicate that esters which are highly toxic to houseflies and mustard beetles are derived from the dibromovinyl and from the dichlorovinyl acid and esters structurally derived from these acids are preferred for this reason.

The stereochemistry of the esters around the cyclopropane ring is such that the esters can exist both as optical isomers and geometrical isomers and our biological investigations have indicated that for the esters which are structurally derived from 3phonoxybenzyl alcohol or its α-cyano analogue - 5 41614 and 2,2-dimethyl-3-(2,2-chloro- or dibromovinyl) cyclopropane carboxylic acid, the esters which are most toxic to houseflies are those derived from the [lR,cis]acid. Our biological investigations have also indicated that the toxicity of these particular esters, even when derived from the ΓlR-transI form of the acid, are still exceptionally high, when compared to the toxicity of existing pyrethroids and, for this reason, the flR.trans1 as well as optically active mixtures of cis and trana isomers aro of interest.

The isomers of the present invention wherein R 3 and R each represent fluorine and R represents 3phenoxybenzyl, a-cyano-3-phenoxybenzyl or 5-benzyl-3furylmethyl have also been found to have an unexpectedly good combination of toxic and knock-down properties with respect to houseflies. Interest in the fluorinated series of esters centres on esters of the ilR.trans1 and ilR.cis] acids.

For compounds of the invention which are substantially pure optical isomers, we are using the nomenclature ilR.cisl and ilR.trans1 as a convenient alternative to the strict nomenclature based on the sequence rule (Cahn. RS., Ingold C and Prelog V, hngew, Chem. Int. Ed. 5 385 (1966) ) where, for example, dihalovinyl cyclopropane carboxylates formally derived from (+)-trans-iIR. 3R~|-chrvsanthemates by replacement of the vinyl methyl groups would be [1R,3S], Xn accordance with our proposal, compounds we previously designated (+)-cis£[lR,3s] and (+)-trans-[lR,3R] are now designated [lR.cis] and flR.trans1 respectively. - 6 41614 When the esters are derived from a-cyano-3phenoxybenzyl alcohol, there is a further site of molecular asymmetry giving rise to a further site of optical activity and these esters are obtainable in the (+), (+) or (-) forms in relation to the stereochemistry of the alcohol part of the molecule.

One of our most toxic compounds to houseflies and mustard beetles is (+)-a-eyano-3-phenoxybenzyl FlR.cisl2,2-dimethyl-3-(2,2-dibromovinyl) cyclopropanecarboxylate. This ester has three centres of asymmetry giving rise to optical isomers, two in the carbon atoms of the cyclopropane ring and the other at the carbon atom bearing the a-cyano substituent. Initially, we prepared this ester by the reaction of (+)-a-cyano-3-phenoxybenzyl alcohol with the acid chloride of the [lR,cis] - acid giving an ester in which the configuration at tho carbon atoms of the cyclopropane ring is retained but which is still racemic at the carbon atom bearing the a-cyano substituent. This product is a mixture of two stereoisomers and we have now found that one of these stereo isomers can be separated from the racemic mixture and that, surprisingly, the stereo isomer which can be separated is a crystalline isomer which exhibits a higher insecticidal activity than the racemic mixture.

The esters of the present invention may be prepared by the methods disclosed in our earlier mentioned application e.g. wherein a carboxylic acid or esterifiable derivative thereof of formula· - 7 41614 C=CH - CH—-CH - COQ' / \ CHg CHg is reacted with a compound of formula RQ, where Q1 and Q are functional groups which, react together to form an ester linkage and R , R and R are as defined in claim 1, the resolution into the desired configuration on the cyclopropane ring taking place before or after formation of the ester linkage. When the ester is to be prepared in the form of a pure optical anchor geometrical isomer in relation to the acid part of the molecule, it is preferred to use the ester precursor in the form of the desired optical and/or geometrical isomer rather than to attempt to resolve the ester after its preparation. Thus, in the case where the ester is prepared by the reaction of an alcohol or derivative thereof with the acid or a derivative thereof, the reaction can be carried out using the appropriate isomer of the acid or derivative thereof, e.g. the ΓlR.cis] isomer. The preparation of trans isomers of the acids is described in our earlier mentioned application. The cis-isomers of the acids can be prepared by modification of the processes described in that complete specification in which the transchrysanthemates are replaced by cis-chrvsanthemates. - 8 ί In order to isolate the stereo Isomer of a-cyano-3-phenoxybenzyl [lR,cis]-2,2-dimethy1-3(2,2-dibromovinyl) cyclopropane carboxylate which ia optically pure at the carbon atom bearing the «-cyano substituent and which is substantially free from other optical isomers, (+)-a-cyano-3-phenoxybenzyl ΓIR,cis 1-2.2-dimethvl-3-(2.2-dibromovinyl)cyclopropane carboxylate may be dissolved in a solvent, particularly a hydrocarbon solvent such as hexane, at a temperature up to 60°C and the solution then cooled, when one of the stereo isomers, having [S] configuration in the alcohol residue will crystallize out from the solution. The crystalline stereo isomer may be removed from the solution, e.g. by filtration and the solution evaporated to dryness to leave a residue comprising the other stereo-isomer, the [R]-isomer, contaminated with small quantities of the [S]-isomer. Nuclear magnetic resonance indicates that the crystalline isomer is substantially one form while the non-crystalline isomer contains traces of the other stereo isomer i.e. the crystalline stereo isomer. While the insecticidal activity of the crystalline stereo isomer is found to be higher than the racemate, the insecticidal activity of the noncrystalline isomer is found to be less than that of the racemate.

The dextro rotatory stereo isomer which can be readily separated from the racemic mixture is derived - 9 41614 from the (-) isomer of the alcohol and the ester has the [S] absolute configuration in tho alcohol residue.

The fluorovinyl cyclopropane carboxylic acids and their salts, acid halides and to alkyl esters 2 3 of formula IIA (R R = F, R=H (or a salt or acid halide thereof) or alkyl) are new compounds which can be prepared by the general method described in our above mentioned application. This involves reaction of an aldehyde of formula XIA with a phosphorane or ylide of formula X under the conditions of the Wittig reaction.

X XIA 3 In formulae X and XIA, R and R are as defined above and R is a group as defined above which will not interfere in the Wittig reaction such as a methyl or tert, butyl group and Z , which in principle can represent any organic radical, will normally be a phenyl radical since the stability of the trisubstituted phosphorus oxide which is formed as the by-product in the reaction is particularly high. The phosphorane of formula X can be prepared in situ by introducing the aldehyde XIA into the reaction mixture together with the triorganophosphine PfZ^)^ and IO 41614 a salt of the appropriate chlorofluoroacetic acid in accordance with procedures lenown per se.

The isomers of the present invention where R represents a 3-phenoxybenzyl, a-cyano-3-phenoxybenzyl or 5-benzyl-3-furylmethyl group can be prepared directly by the Wittig reaction mentioned above by using a starting aldehyde of appropriate configuration in which R represents the required ester group required in the final product in accordance with the second method disclosed in our earlier mentioned application.

The esters of this invention may be formulated into insecticidal compositions of the type described in our earlier mentioned application and the compounds and the compositions may be used to control insects in the manner described in our earlier mentioned application.

The following examples are given to illustrate the invention: Refractive indices are measured at 20°C.

EXAMPLE 1 Methyl-flR,cis 1-caronaldehvde was obtained by ozonolysis of methyl (+)-cis-chrvsanthemate. Tho procedure described in Example 16 of our above identified application was then repeated using 5.3 g triphenylphosphine, 3,36 g. carbon tetrabromido and 60 mis. dry dichloromethane and 1.5 g methyl-ΓIR.cis 1caronaldehyde. The reaction product was then refluxed 3 hours with 9 mis. acetic acid, 6 mis. concentrated HBr and 3 mis. water and then diluted with water and extracted with other. The organic solution was extracted with - 11 416 14 dilute sodium hydroxide and this extract acidified and extracted with ether and evaporated to give a residue of fIR;cis]-2,2-dimethyl-3-(2,2-dibromovinyl)cyclopropane' carboxylic acid.

The carboxylic acid described above was converted to its acid chloride by reaction with thionylchloride in pyridine as described in Example 17 of our above identified application and the resulting acid chloride reacted with 3-phenoxybenzyl alcohol in dry benzene in the presence of pyridine as described in Example 17 of our above identified application to give 3-phenoxybenzyl ΓIR,cis 1-2,2-dimethy1-3(2,2-dibromovinyl)cyclopropane carboxylate mp 93°, ηθ 1.5848. (Compound P29A).

The esterification described above was repeated by replacing 3-phenoxybenzyl alcohol by (+)-a-cyano-3-phenoxybenzyl alcohol to give (+)-acyano-3-phenoxybenzyl [lR,cis]-2,2-dimethy1-3-(2,2 dibromovinyl) cyclopropane carboxylate nD 1.5732 (Compound P29 B).

EXAMPLE 2 The esterification procedures described in Example 1 were repeated replacing the ΓlR.cisldibromovinyl acid by [IR,trans.1-2.2-dimethyl-3“ (2,2-dibromovinyl)-cyclopropane carboxylic acid (obtained as described in Example 16 and 17 of our above identified application), [lR,trans]-2,2-dimethyl-3(2,2-dichlorovinyl)cyclopropane carboxylic acid (prepared as described in Example 15 and 17 of our above identified application). The following esters were prepared: 3-phenoxybenzyl[IR, trans]-2,2-dimethyl3-(2,2-dibromovinyl) cyclopropane carboxylate Πρ 1.5828 (Compound P29C). (+)-a-cyano-3-phenoxybenzyl ΓIR-trans12.2- dimethyl-3-(2,2-dibromovinyl) cyclopropane carboxylate, nQ 1.5664 (Compound P29D). (+)-a-cyano-3-phenoxybenzyl [IR.trans110 2,2-dimethyl-3-(2,2-dichlorovinyl) cyclopropane carboxylate, ηθ 1,5498 (Compound P29E). (+)-a-cyano-3-phenoxybenzyl [IR,cisl2.2- dimethyl-3-(2,2-dichlorovinyl) cyclopropane carboxylate, (Compound P29J), nD 1.5622.

The required isomer of the acid for the last mentioned ester was obtained by resolution as described in Example 5. - 13 41614 EXAMPLE 3 ( + )- 2° [a]jj = -1 (C=0.4 in ethanol) nD 1.5732 N. M.R: peaks associated with the C-H 1° group (carbon atom bearing the α-cyano substituent) T = 3.65 and 3,72 (equal areas).

O. 6 grams of the racemate was dissolved in 25 ml. hexane and maintained at -20°C until precipitation of crystals was complete. The crystals were 15 then filtered off and recrystallised from hexane to give the [lR,cis]-2,2-dimethyl-3-(2,2-dibromovinyl) cyclopropane carboxylate of (-)- m.p. 100°C [«]q° + 16° (0=0.4 in ethanol) N.M.R. peaks associated with the C-H group (carbon atom bearing the α-cyano substituent)T= 3.65 but no peak atf= 3.72.

The mother liquors were combined and evaporated to dryness to give 0.32 g of the non-crystalline isomer of the [lR,cis]-2,2-dimethyl-3-(2,2-dibromovinyl) cyclopropane carboxylate of (+)-«-cyano-3-phenoxybenzyl alcohol having the following properties: nQ 1.5749 [α]2θ - 15° (C=0.4 in ethanol) This isomer has [R] configuration at the carbon atom carrying the «-cyano group.

N.M.R. peaks associated with the ,C-H bond (carbon atom bearing the «-cyano group)T = 3.72 with a small peak (20% of the 3.72 peak) at T = 3.65 attributable to the crystalline isomer.

In the above examples, temperatures are in degrees centigrade and refractive indices are measured at 20°C.

The insecticidal toxicity of the compounds described in Examples 1-3 were tested against houseflies and mustard beetles by the procedures described in our above identified application and the following relative toxicities were obtained in relation to 5-benzyl-3furylmethyl (+)-trans-chrvsanthemate which is arbitrarily assigned a toxicity of 1000.

Compounds Houseflies Mustard Beetles 5-benzy1-3-furylmethyl-(+) trans-chrvsanthemate 1,000 1,000 P29A 2,200 1,600 P29B 10,000 11,000 [S] isomer of Compound P29B 23,000 14,000 [R] isomer of Compound P29B 3,500 4,000 P29C 1,100 4,000 P29D 4,100 5,200 EXAMPLE 4 Expi'i inuvit A [IR,-Trans]3-(2,2-difluorovinyl)-2,2-dimethyl cyclopropane carboxylic acid a) A mixture of freshly distilled, dry, dimethyl fotmamidc (20 ml), triphenylphosphine (7.9 g), methyl [IR,-transΊ-caronaldehyde (3.0 g) and the sodium salt of chlorodifluoro acetic acid (3.6 g) were heated at 90°C with stirring for 20 hours. Water (60 ml) was lo then added and the solution extracted with 2 x 30 ml portions of diethylether. The combined ethereal extracts were washed with water, saturated sodium carbonate solution, saturated sodium chloride solution, and then dried over sodium sulphate and the ether distilled off.

Distillation of the residue gave 2.25 g of methyl [ IR,-trans)-3-(2,2-difluorovinyl)-2,2-dimethyl cyclop:op,me carboxylate, b.p. 63°C/2O mm, nQ 1.4209. b) An alkaline solution was prepared by dissolving sodium hydroxide (200 mg) in water (1 ml) and ethanol (10 ml) was added. . The .methyl ester described above (0.5 g) was stirred into the alkaline solution and the mixture was refluxed for 1 hour. The solvents were removed under reduced pressure and water (30 ml) added. The solution was washed with 2 χ 20 ml portions of diethylether and acidified with concentrated hydrochloric acid. The mixture was extracted with 2 x 30 ml portions of diethylether, washed with saturated sodium chloride solution, dried over sodium sulphate and the solvents evaporated to leave 410 mg of ΓIR,-trans-] - 16 41614 3-(2,2-difluorovinyl)-2,2-dimethyl cyclopropane carboxylic acid as an oil having 1.4400.

Experiment B ΓlR,cis1-3-(2,2-difluorovinyl)2,2-dimethyl cyclopropane carboxylic acid a) The procedure described in Example 4a above was repeated using 1.5 g me thylΓIR,-ci s1-caronaldehyde, 2.92 g triphenylphosphine, 1.2 g sodium chlorodifluoro acetate and 7 ml dimethylformamide. The residue obtained after evaporating the final diethyl ether extract was itself extracted with 3 x 40 ml portions of petroleum ether and the petroleum ether evaporated and the residue distilled to give 440 mg of methyl [IR,-cis)3-(2,2-difluorovinyl)-2,2-dimethyl cyclopropane carboxylate b.p. 74 - 78°C/2O mm, nQ 1.4288. b) The methyl ester obtained above (380 mg) was added to a solution of sodium hydroxide (200 mg) in water ( 1 ml) and ethanol (10 ml). The mixture was refluxed for 1 hour with stirring and the solvents removed under reduced pressure. Water (50 ml) was then added and the solution washed with 20 ml diethylether, acidified with concentrated hydrochloric acid and extracted with diethyl ether. The ethereal extract was washed with saturated sodium chloride, dried over sodium sulphate and evaporated to give 290 mg of ΓIR,-cis 1-3-(2,2-difluorovinyl)-2,2-dimethyl cyclopropane carboxylic acid, nD 1.4456. - 17 ( The acids described in Experiments A and B were then esterified with 5-benzyl-3-furylmethyl alcohol, 3-phenoxybenzyl alcohol and (+)- r> A solution of the acid (110 mg) in benzene (5 ml) was treated with pyridine (50 (il) and thionyl chloride (45 μΐ) and left to stand for three hours at the end of which time, the acid has been converted into its acid chloride. A solution of 3-phenoxybenzyl alcohol (137 mg) or an equivalent quantity of the other alcohols and pyridine (50 μΐ) in benzene (5 ml) was added to the acid chloride and the mixture left to stand over night. The desired ester was recovered from the solution by passing it through a column of neutral alumina and eluting the column with benzene.

The eluate was evaporated to leave the ester as an oil, tho following results being obtained. Compound Acid Alcohol —d P31A IR,-trans 5-benzyl-3-furyl methyl 1.5142 P31B IR,-trans 3-phenoxy-benzyl 1.5293 P31C IR,-trans (+)-a-cyano-3- phenoxy-benzyl 1.5330 P31D IR,-cis 5-benzyl-3-furyl methyl 1.5136 P31E IR,-cis 3-phenoxybenzyl 1.5349 P31F IR,-cis (+)-a-cyano-3- phenoxybenzyl 1.5355 EXAMPLE 5 ( + )-cls-trang- 2,2-dimethyl-3-(2,2-dichlorovinyl) cyclopropane carboxylic acid, prepared by reacting ethyl diazoacetate with 1,l-dichloro-4-methylpenta-1,3-diene and hydrolysing the resulting ethyl ester, was separated into the (+)-cis and (+)-trans isomers by selective crystallisation in n-hexane, in which the cis isomer is more soluble. The substantially pure cis and trans isomers were then resolved into their individual optical isomers by the following procedure. Resolution of (+)-cis-2,2-dimethyl-3-(2,2-dichlorovinyl)cyclopropanecarboxylic acid. The (+)-cis acid (14.6 g) in benzene (250 ml), and (+)-a-methylbenzyIamine (8.47 g) in benzene (30 ml) were mixed at 50°, and allowed to cool to 20° overnight. The precipitate (13.2 g, 58% required isomer) was recrystallised 3 times from benzene to give the (+)-α-methyl benzylamine salt of the [IS,-cis] acid (1.7 g) m.p. 135° [<*]jj -17.1° (c, 1.6 in EtOH) was isolated. Repetition, using (-)-a-methylbenzylamine gave, after 3 crystallisations, the (-)-amethyl-benzylamino salt of the [lR.-cisl acid (6.1 g) m.p. 147° [α]ρ-26.1ο (c,1.9 in EtOH) and from the mother liquors the (-)-o-methylbenzylamine salt of the [IS,-cis] acid (3.8 g) m.p. 139° [a]jj + 14.8° (c,2.0 in EtOH).

Each of the four salts was shaken with benzene (50 ml) and 3N HCl (50 ml) and the benzene layer processed to give the resolved acids. Thus were obtained [IS,-cis]-2,2-dimethyl-3-(2,2-dichlorovinyl) cyclopropane carboxylic acid (4.6 g) m.p. 90° [D -26.9° (c, 1.7 in CHCl^) and f!R,-cis1-2,2-dimethvl-3(2,2-dichlorovinyl) cyclopropane carboxylic acid (3.9 g) m.p. 90° [a]D + 27.2° (c, 2.1 in CHC13).

Resolution of (+)-trans-2,2-dimethyl-3(2,2-dichlorovinyl)cyclopropane carboxylic acid.

The (+)-trans acid (15.6 g) in benzene (180 ml) and L-(+)-threo-l-p-nitro-phenyl-2-N,N-dimethylaminopropahe~l,3-diol (18.0 g) in benzene (180 ml.) were mixed at 50° and cooled to 20° during 2 days. The precipitate (14.2 g) was recrystallised 3 times from trichloroethylene to give the L-(+)-threo-l-pnitrophenyl-2-N,N-dimethylaminopropane-1,3-diol salt of [IS,-trans]-2,2-dimethyl-3-(2,2-dichlorovinyl) cyclopropanecarboxylic acid (8.9 g) m.p. 129-131° [a]D + 7.4° (c, 2.1 in EtOH). Correspondingly D-(-)-threo-l-p-nitrophenyl-2-N,N-dimethylaminopropanel, 3-diol gave the salt with the flR.-trans] acid (9.4 g) m. p. 129-131°, [«]D~7.3° (c, 2.0 in EtOH). Decomposition of the salts with 3N HCl as described for the cis acids gave [IS,-trans1-2,2-dimethvl-3-(2,2-dichlorovinvl cyclopropane carboxylic acid (3.8 g) m.p. 68-73°, [«]ρ~ 34.6° (c, 1.9 in EtOH) and Γ!R.-trans1-2.2-dimethvl-3(2,2-dichlorovinyD cyclopropane carboxylic acid (4.1 g) m.p. 69-73°, [a]D + 33.0° (c, 2.0 in EtOH).

The riR.-cis] and flR,trans1 acids were converted to their acid chloride and reacted with 3-phenoxybenzyl alcohol by the procedure described in Example 1 to give the 3-phenoxybenzyl ester of [lR,-cis] and of [IR,rtrans-1 2,2-dimethyl-3-(2,2-dichlorovinyl)-cyclopropane carboxylic - 20 41614 acid, compounds P29L and P29M respectively.

The [IR, -cis]acid was also esterified with 5-benzyl3-furylmethyl alcohol by the same procedure to give compound P29N, 5-benzyl-3-furyImethyl ClR'.-crs-l 2,2-dimethyl-3-(2,2-dichlorovinyl) cyclopropane carboxylate.

The toxicity of these new esters was tested by the procedure described in detail in our above mentioned application and the following results were obtained: Compounds Relative Toxicity Houseflies Mustard Beetles 5-benzyl-3-furyImethyl r lR-transj-chrysanthemate (Bioresmethrin) P29L P29M P29N 1,000 1,600 740 2,600 1,000 1,400 2,100 2,200 The toxicity of compounds P29L and P29M relative to bioresmethrin was also determined against the American cockroach, Periplaneta americana L·. with the following results.

Compound Relative Toxicity Bioresmethrin 100 * P29L 2,100 P29M 800 * LDg0=2.5s/jg/insect

Claims (18)

1. A cyclopropane carboxylic acid ester of the general formula: „2 C=CH-CH-CH-COOR IIA CH. CIL 5 wherein the compound is in the form of a substantially pure optical isomer with respect to the cyclopropane ring and having the [rJ configuration at the carbon atom 2 of the cyclopropane ring carrying the COOR group and R and r\ which may he the same or different» each 10 represent fluorine, chlorine or bromine and R represents 3-phenoxybenzyl or a-cyano-3-phenoxybenzyl or, when 2 3 at least one of R and R represents fluorine, or 2 3 when R and R each represent chlorine and the cyclopropane ring has the [lR,cis] configuration, R may 15 also represent 5-benzyl-3-furylmethyl. , 2

2. An isomer according to claim 1, wherein R 3 and R each represent chlorine or each represent bromine.

3. An isomer according to claim 1 wherein R 3 and R each represent fluorine. 20

4. An isomer according to any one of the preceding claims, wherein the isomer is in the form of a substantially pure flR,cis1 isomer about the cyclopropane ring. 22 41614

5. An isomer according to any one of claims 1 to 3. in the form of a substantially pure flR,trans] isomor or a mixture of a ΓIR.trans] isomer with a [IR.cis] isomer.

6. A (+)-α-cyano-3-phenoxybenzyl ester of ΓIR,trans1- or ΓIR,cis 1-2.2-dimethyl-3-(2.2-dibromovinyl) cyclopropane carboxylate.

7. [sJ-a-cyano-3-phenoxybenzyl [lR,cis]-2.2dimethyl-3-(2,2-dibromovinyl) cyclopropane carboxylate.

8. A 3-phenoxybenzyl-. rt-cyano-3-phenoxybenzylor 5-bonzyl-3-furylmethyl ester of IIR.cis) or of ΓIR.trans1 2.2-dimethyl-3-(2.2-difluorovinyl) cyclopropane carboxylate.

9. 3-Phenoxyben2yl ΓIR.trans] or 1IR.cis] 2,2-dimethyl-3-(2,2-dichlorovinyl) cyclopropane carboxylate.

10. 5-Benzyl-3-furylmethyl IIR.cis] 2,2-dimethyl3-(2,2-dichlorovinyl) cyclopropane carboxylate.

11. A process for the preparation of an isomer as defined in claim 1 wherein a carboxylic acid or esterifiable derivative thereof of formula: C=CH - CH - CH - COQ' 3 Z \ / R C / \ ch 3 ch 3 is reacted with a compound of formula RQ. where Q* and Q are functional groups which react together to form an ester 2 3 linkage and R , R and R are as defined in claim 1, the resolution into the desired configuration on the cyclopropane ring taking place before or after formation of the ester linkage. I 5

12. A process for the preparation of the isomer defined in claim 7 which comprises dissolving (+)-α-cyano-3-phenoxybenzyl [IR , cis]-2.2-dimethyl-3(2.2-dibromovinyl) cyclopropane carboxylate in a solvent, cooling the, solution and recovering the χο stereoisomer having [sj-configuration at the carbon atom carrying the α-cyano group.

13. A process for the preparation of an isomer as defined in claim 1 wherein a phosphorane or ylide of formula is reacted under the conditions of the Wittig reaction with an aldehyde of formula 0 = CH-CH - CH - COOR \ / C / \ CHg CHg where R 2 , R 2 and R are as defined in claim 1 and Z** is an organic radical that forms a stable triorgano phosphorous oxide, the resolution into the desired configuration at the cyclopropane ring taking place before or after the Wittig reaction. - 24 41614

14. A process according to any one of claim 11 to 13 substantially as described in any one of tho Examples.

15. An ester obtained by a process according to any one of claims 11 to 14.

16. An insecticidal composition comprising an ester according to anyone of claims 1 to 10 or 15 together with a diluent or carrier.

17. A method of insect control by applying to an insect or to an environment susceptible to insect attack an ester according to any one of claims 1 to 10 or 15 or a composition according to claim 16.

18. A substantially pure optical isomer of a compound of the formula F. C = CH - CH - CH - COOR CH. CH. wherein R represents hydrogen (or a salt or acid halide thereof) or an alkyl group of 1 to 4 carbon atoms, having the [rJ configuration at the carbon atom of the cyclopropane ring carrying the COOR group.