David A. Pulman

The pyrethrins and related compounds. Part XVIII. Insecticidal 2,2-dimethylcyclopropanecarboxylates with new unsaturated 3-substituents

Fifty new esters related to the insecticide bioresmethrin [5-benzyl-3-furylmethyl (1R,3R)-2,2-dimethyl-3-(2-methylprop-1-enyl) cyclopropanecarboxylate], having various groups in place of the 2-methylprop-1-enyl side chain, have been synthesised. cis- and trans-3-Formyl-2,2-dimethylcyclopropanecarboxylic esters are obtained by ozonolysis of the corresponding chrysanthemates. Wittig and other reactions with these esters then give the required products. 5-Benzyl-3-furylmethyl esters are obtained by transesterification or via acids obtained by cleavage of t-butyl esters under mild conditions.

Deltamethrin: the cream of the crop.

Replacement of the pyrethronyl alcohol portion of the natural pyrethrins with the 5-benzyl-3-furylmethyl moiety gave bioresmethrin, a synthetic pyrethroid of high potency and safety but with limited photostability. Introduction of novel substituents at the 3-position of the cyclopropane ring then led to the discovery of insecticidally active compounds with greatly improved potency. Systematic changes of both the alcohol and acid components gave second-generation pyrethroids (permethrin, cypermethrin, and deltamethrin) with improved potency and photostability suitable for agricultural use. Metabolic studies showed that the photostabilized compounds remained biodegradable. Deltamethrin, discovered in 1974, was the cream of the crop and remains 36 years later as one of the most important synthetic pyrethroid insecticides.