Pyrethroid insecticides derived from 2,2'-bridged biphenyl-3-ylmethanols

The addition of a hydrocarbon bridge between the 2‐ and 2′‐positions in biphenyl constrains the twist angle between the two phenyl rings to fairly small limits. It has been found that the biological activity of a series of pyrethroid esters, of hydrocarbon bridged biphenyl‐3‐ylmethanols and of heterocyclic hydrocarbonbridged biphenyl analogues, changes with the length of the bridge. The optimum activity and the maximum biological activity spectrum were found for the esters of three‐carbon bridged alcohols. The relationship of the activity to the twist angle for these bridged esters was compared with the activity and spectrum of a series of biphenyl and heterocyclic biphenyl analogues previously reported. A parallel exists between the two series. The optimum twist angle between the aromatic rings of the alcohols, in both the bridged and free rotating analogues, is around 50°. Pyrethroid esters showing the highest activity were produced from 6, 7‐dihydro‐5H‐dibenzo‐[a,c]cyclohepten‐4‐ylmethanol. The biological activity of a series of pyrethroid esters of this alcohol is also reported.