The synthesis of difluorinated analogue of an insect sex pheromone has been accomplished through intramolecular radical cyclization and lipase-catalyzed reaction. Optically active alpha,alpha-difluoroeldanolide and its antipode have been synthesized. Dose-response curves constructed from electroantennogram responses of female moths showed the difluoroanalogues to be-as active as the natural pheromone. (C) 1998 Elsevier Science Ltd. All rights reserved.