METHOD OF PRODUCING CRYSTALLINE EQUIMOLECULAR MIXTURE OF PAIR OF ENANTHIOMERS OF (S)-ALPHA-CYANO-(3-PHENOXY0BENZYL)-1R-CIS-3(2,2-DICHLORVINYL)-2,2-DIMETHYLCYCLOPROPANECARBOXYLATE AND (R)-ALPHA-CYANO-(3-PHENOXYBENZYL)-1S-CIS-3-(2,2-DICHLORVINYL)-2,2-DIMETHYLCYCLOPROPANECARBOXYLATE

摘要

This invention relates to the preparation of cyclopropane carboxylic acid ester derivatives, which are useful as pesticides. There is provided a process for preparing a mixture of cis-isomers of a compound of formula IMAGE (I) wherein R1 and R2 are independently selected from chlorine, bromine and methyl, consisting predominantly of the 1R cis S- and 1S cis R- isomers, which process comprises dissolving a mixture of 1S cis S- and 1R cis R- isomers of the compound of formula I, alone or in the presence of 1R cis S- and 1S cis R-isomers, in an organic amine base containing from 5 to 7 carbon atoms and being a secondary amine containing two branched alkyl groups or a tertiary amine, crystallizing out from a resulting solution of cis- isomers of formula I in the organic amine base a 1:1 mixture of the 1R cis S- and 1S cis R- isomers, and evaporating off the organic amine base. The process of the invention yields a product which may contain up to twice as much of the most active isomer of the compound of formula I as a racemic mixture of all four cis-isomers, and is a readily effected process which does not involve any sterospecific synthesis or optical resolution steps.