Biphenylmethyl pyrethroids

Replacement of the normal pyrethroid ester by alternative linkages usually leads to diminution of biological activity. One important exception to this general phenomena is several oxime ether derivatives, in particular, 3-phenoxybenzyl derivatives of various alkyl aryl ketones. Pyrethroid esters derived from certain 2-substituted-[1,1 -biphenyl]-3-methanols have been shown to possess initial and residual activity surpassing that of esters derived from 3-phenoxybenzyl alcohol. Now it has been demonstrated that the same enhancement of activity was observed for alkyl aryl oxime ethers of certain [1,1 -biphenyl]-3-methanols compared to the corresponding 3-phenoxybenzyl alcohol derived oximes. The synthesis, biological activity, including soil activity, structure-activity relationships and toxicity of several of these biphenylmethyl oxime ethers are described. 

One of the more recent results of pyrethroid research in the late 1970 s/early 1 80 s consists of biphenyl-3-methylesters of certain pyrethroid acids, having an additionally strong activity against mites (Bifenthrin). Although the unsubstituted biphenylmethyl esters are of an appreciable activity [659, 660], the higher substituted ones are more interesting, particularly if the phenyl substituent is sterically forced out of plane. For synthesis, the classical methods of biphenyl chemistry had to be optimized to quite an extent (Reaction scheme 215). 

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