The pyrethrins and related compounds. Part XXII. Preparation of isomeric cyano‐substituted 3‐phenoxybenzyl esters

Preparation of 3‐phenoxybenzyl chrysanthemates and their dihalovinyl analogues substituted with a cyano group at the 2‐, 6‐, (R)‐α‐, or (S)‐α‐ positions is described. The (R)‐ and (S)‐ isomers of α‐cyano‐3‐phenoxybenzyl esters of 2,2‐difluoro‐, ‐dichloro‐, and ‐dibromo‐vinyl analogues of cis‐ and trans‐ chrysanthemic acid are separated chromatographically, as are the separate pairs of enantiomers of fenvalerate, (RS)‐α‐ cyano‐3‐phenoxybenzyl (RS)‐2‐(4‐chlorophenyl)‐3‐methylbutyrate. An optically active ester of α‐cyano‐3‐phenoxybenzyl alcohol (obtained using D‐oxynitrilase) with 2,2,3,3‐tetramethylcyclopropanecarboxylic acid is synthesised.