Synthesis of trifluoromethyl ketones as inhibitors of antennal esterases of insects.

A variety of long chain aliphatic and aromatic trifluoromethyl ketones I-XIV has been conveniently prepared, many of them for the first time, from the corresponding Grignard or organolithium derivatives. Two of them, (Z)-1,1,1-trifluoro-15-octadecen-13-yn-2-one (XV) and (Z)-1,1,1-trifluoro-16-nonadecen-14-yn-2-one (XVI), structurally-closed analogues of (Z)-13-hexadecen-11-ynyl acetate, the sex pheromone of the processionary moth Thaumetopoea pityocampa, have been stereospecifically synthesized in excellent yield by a convenient new method. The procedure involves lithiation of the corresponding iododerivative XXIX and XXX with one equivalent of tert-BuLi to obviate addition of the reagent to the enyne system. Some of the compounds have already been tested and found to be good inhibitors of antennal esterases in the Egyptian armyworm Spodoptera littoralis and the pheromone action in the processionary moth Thaumetopoea pityocampa. beta-Thiotrifluoromethyl ketones XVII-XX, which are expected to enhance the inhibition activity of the parent ketones due to their higher hydration constants, have also been prepared in good yields.