S-((Phenylsulfonyl)difluoromethyl)thiophenium Salts: Carbon-Selective Electrophilic Difluoromethylation of p-Ketoesters, β-Diketones, and Dicyanoalkylidenes

摘要

S-((Phenylsulfonyl)difluoromethyl)thiophenium salts were designed and prepared by a triflic acid catalyzed intramolecular cyclization of ortho-ethynyl aryldifluoromethyl sulfanes. The thiophenium salts were found to be efficient as electrophilic difluoromehtylating reagents for introduction of a CF2H group to sp3-hybridized carbon nucleophiles such as of fi-ketoesters and dicyanoalkylidenes. The (phenylsulfonyl)di-fluoromethyl group can be readily transformed into CF2H under mild reaction conditions. Enantioselective electrophilic difluoromethylation was also achieved in the presence of bis(cinchona) alkaloids.