Synthesis of Difluoroalkenes from Thiocarbonyl Compounds via Difluorothiiranes: Electrophilic Counterpart to Wittig-Type Difluoromethylidenation

Abstract The synthesis of 1,1-difluoro-1-alkenes was achieved by the treatment of dithioesters and thioketones with trimethylsilyl 2-fluorosulfonyl-2,2-difluoroacetate in the presence of a proton sponge catalyst, namely, 1,8-bis(dimethylamino)naphthalene. The generated electrophilic difluorocarbene (:CF2) reacted with the thiocarbonyl functionalities to form 2,2-difluorothiirane intermediates, desulfurization of which afforded the products in a Barton–Kellogg-type difluoromethylidenation. The reaction described herein is an electrophilic counterpart to the Wittig-type (nucleophilic) difluoroalkene synthesis starting from carbonyl compounds. The electrophilic difluoromethylidenation facilitated the synthesis of sulfanylated and diarylated 1,1-difluoroalkenes, including sterically hindered ones, which are inaccessible by nucleophilic difluoromethylidenation.