gamma-Cyhalothrin → (1RS)-cis-3-(Z-2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclopropanecarbonyl chloride

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There is therefore provided a process for the preparation of gamma-cyhalothrin comprising a) chlorinating 1R cis-Z 3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethyl cyclopropanecarboxylic acid (V) to give 1R cis-Z 3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethyl cyclopropanecarboxylic acid chloride (III); b) esterifying 1R cis-Z 3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethyl cyclopropanecarboxylic acid chloride (III) with 3-phenoxy benzaldehyde (IV) in the presence of a source of cyanide to form a diastereoisomeric mixture of 1R cyhalothrin isomers (II) and c) epimerising the diastereoisomeric mixture (II) under conditions in which the least soluble diastereoisomer (I) crystallises from solution.

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