Carbocyclization reactions of terminally difluorinated alkenyl active methine compounds mediated by SnCl₄ and amine

Carbocyclization of terminally difluorinated 3-butenyl active methine compounds 1a-1e proceeded through the 5- endo mode, upon treating with SnCl₄ and triethylamine to give fluorocyclopentene derivatives 3a-3e. Iodocarbocyclization of dimethyl 2-(4,4-difluorobut-3-enyl)malonate (1a) mediated by I₂, SnCl₄ and amine provided 2,2-difluoro-3-iodocyclopentane-1, 1-dicarboxylate 4a through the 5-endo mode, while in the case of 2-(5,5-difluoropent-4-enyl)malonate (1f) 5-exo mode cyclization reaction took place to give difluoroiodomethylcyclopentane derivative 5f.