Systematic synthesis of multifluorinated alpha,alpha-difluoro-gamma-lactones through intramolecular radical cyclization

Carbon radicals from allyl O-(trimethylsilyl)-alpha-bromo-alpha,alpha-diflu oro acetal can cyclize onto the olefinic part regiospecifically to give gam ma-lactols in good yield. The lactols are then converted to the correspondi ng alpha,alpha-difluoro-gamma-lactones. Systematic synthesis of multifluori nated-alpha,alpha-difluoro-gamma-lactones has thus been accomplished throug h intramolecular radical cyclization as a key reaction. Semiempirical MO ca lculation study suggested a unique nature of alpha,alpha-difluoroacetate in that complete delocalization of the electrons in the SOMO orbital of alpha ,alpha-difluoroacetyl radical occurred; this caused unsuccessful cyclizatio n. To apply the present radical reaction, the first synthesis of both enant iomers of difluoroeldanolide, analogues of the sex pheromone of the male Af rican sugarcane borer, has been demonstrated. Electrophysiological tests re vealed that the difluorinated analogues were as active as the natural eldan olide on the olfactory receptors.