14 C‐labelling of optically active fenvalerate, α‐cyano‐3‐phenoxy‐benzyl (S)‐2‐(4‐chlorophenyl)‐3‐methylbutyrate (I)

(S)‐Fenvalerate (α‐cyano‐3‐phenoxybenzyl) (S)‐2‐(4‐chlorophenyl)‐3‐methylbutyrate, a novel insecticide, was labelled with carbon‐14 individually at the carbonyl ( 1a ), the cyano ( 1b ) and the alcoholic methyne ( 1c ) carbons for use in metabolic studies. Isopropylation of 4‐chlorophenylacetonitrile‐ 14 C with isopropyl bromide followed by hydrolysis gave racemic 2‐(4‐chlorophenyl)‐3‐methylbutyric‐1‐ 14 C acid, which on optical resolution with (−)‐1‐phenylethylamine gave the (S)‐acid. Esterification of the (S)‐acid with α‐cyano‐3‐phenoxybenzyl bromide gave 1a in 18% yield from potassium cyanide‐ 14 C. Esterification of α‐cyano‐ 14 C‐3‐phenoxybenzyl alcohol with (S)‐2‐4‐chlorophenyl‐3‐methyl‐butanoyl chloride ( 9 ) gave 1b in 65% yield. Condensation of 3‐phenoxybenzaldehyde‐(carbonyl‐ 14 C), prepared from 3‐phenoxybenzoic‐ 14 C acid, with 9 and sodium cyanide gave 1c in 54% yield from barium carbonate‐ 14 C.