AbstractPyrethrin‐like esters of a new type were obtained by reaction of the 4‐bromo derivatives of esters (Et, Pr, Ph) of 3‐methylcyclopent‐2‐enone‐2‐acetic acid with silver chrysanthemates. The structure of the intermediate bromo compounds and hence of the esters was deduced from the ease with which hydrogen bromide was eliminated by tertiary amines to give cyclopentadienones. 2‐Acetonyl‐3‐methylcyclopent‐2‐enone was prepared and by similar reactions gave a chrysanthemyl derivative.