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.