Tuning efficiency of the 4-exo-trig cyclization by the electronic effect: ring closure of 3,3-difluoro-4-pentenyl carbon radicals and synthesis of a gem-difluorocyclobutane nucleoside.

4-exo-trig Cyclization reaction of a 4-pentenyl carbon radical containing the gem-difluoromethylene moiety adjacent to a radical accepting α,ß-unsaturated ester was found to proceed efficiently to furnish a novel gem-difluorocyclobutane derivative. The cyclized product could be transformed into a gem-difluoromethylene analogue of oxetanocin T.