Selective Synthesis of Spirobiindanes, Alkenyl Chlorides, and Monofluoroalkenes from Unactivated Gem-Difluoroalkanes Controlled by Aluminum-Based Lewis Acids

Abstract

The highly selective synthesis of spirobiindanes, alkenyl chlorides, and monofluoroalkenes via the cleavage of inert C(sp³)-F bonds in unactivated gem-difluoroalkanes using readily available and inexpensive aluminum-based Lewis acids of low toxicity is reported. The selectivity of this reaction can be controlled by modifying the substituents on the central aluminum atom of the promoter. An intramolecular cascade Friedel-Crafts alkylation of unactivated gem-difluorocarbons can be achieved using a stoichiometric amount of AlCl₃. The subsequent synthesis of alkenyl chlorides via F/Cl exchange followed by an elimination can be accomplished using AlEt₂Cl as a fluoride scavenger and halogen source. The defluorinative elimination of acyclic and cyclic gem-difluorocarbons to give monofluoroalkenes can be achieved using AlEt₃.

Keywords: fluorine, aluminum, C-F bond activation, spiro, fluoroalkenes, alkenyl chlorides