Free-radical approach to the synthesis of fluorine-substituted cyclic compounds. Cyclization reactions of trifluoromethyl-and difluoromethylene-substituted carbon radicals

Abstract

Trifluoromethyl- or difluoromethylene-substituted alkyl radicals (CF 3C or CF 2C) and trifluoromethyl- substituted alkenyl radicals (CF 3CC) cyclize effectively intramolecularly to allow the synthesis of fluorine- substituted cyclic compounds. Radical reactions of thiocarbonylimidazolide derivatives ( 7a,b, 13a–d, 14e,f) gave CF 3-substituted cyclopentane derivatives ( 22a, 25a–d) or cyclohexane derivatives ( 22b, 26e,f) via 5- or 6- exo selective cyclization. CF 3-substituted cyclopentene derivatives ( 27a,b) or cyclohexene derivatives ( 27c) were also obtained from alkenyl iodides ( 17a–c) via radical cyclization. Cyclopentane derivatives ( 29a–f, 31) containing the CF 2CO 2Et group were synthesized by Reformatsky reaction and radical cyclization.