Synthesis of 6,6-Difluorocyclopropa[b]furo[2,3-c]pyrrole and 7-Fluoro furo[3,2-c]pyridine Derivatives via 1,5-Electrocyclization of CarbeneDerived Azomethine Ylides

Reaction of N-(5-R-furan-2-ylmethylidene)anilines with difluorocarbene, generated in CF2Br2/Pb*/Bu4NBr/ultrasound system proceeds via 1,5electrocyclization of intermediate azomethine ylides to give 6,6difluorocyclopropa[b]furo[2,3-c]pyrrol-4(5H)-one or/and 4,4,6,6tetrafluorocyclopropa[b]furo[2,3-c]pyrrole derivatives. Thermolysis of these compounds under solvent-free conditions gives rise to 2,5disubstituted 7-fluoro-4,5-dihydrofuro[3,2-c]pyridine-4(5H)-ones in high yields.