THE SYNTHETIC PYRETHROID ISOMERS .1. PREPARATION

Enantiomers and racemic mixtures of selected benzilic esters using res olved and raceme permethrinic or chrysanthemic acids of high purity we re synthesised via improved methods based on conventional steps. Nine basic structures of selected derivatives having hydrogen, bromo or phe noxy group at meta position were prepared including the well known ins ecticides of phenothrin, permethrin and cypermethrin. The optical puri ty of these compounds were determined via an NMR method applying chira l shift reagents. The configuration of the isomers of new a-cyano-benz yl esters were assigned via a rule realized by comparing the character istic 1H NMR shifts of the dimethyl groups attached to the cyclopropan e ring.