AbstractOver 100 benzyl esters of pyrethroidal acids were synthesised and tested for insecticidal activity to establish detailed structure–activity relationships in compounds with side‐chains similar to those in the natural pyrethrins. Alkenyl, and corresponding alkynyl, side‐chains were effective, both at the 3‐ and 4‐positions, as were side‐chains with extended substitution in eitherEorZforms. A cyano group at the α‐position increases activity if the side‐chain is at C‐3, but lowers it drastically if the substituent is at C‐4. Similarly, methyl groups at C‐2 and/or C‐6 may increase activity whether the unsaturated side‐chain is at C‐3 or C‐4, but only in t
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