S-((phenylsulfonyl)difluoromethyl)thiophenium salts: carbon-selective electrophilic difluoromethylation of ß-ketoesters, ß-diketones, and dicyanoalkylidenes.

ABSTRACT

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 CF2 H group to sp(3) -hybridized carbon nucleophiles such as of ß-ketoesters and dicyanoalkylidenes. The (phenylsulfonyl)difluoromethyl group can be readily transformed into CF2 H under mild reaction conditions. Enantioselective electrophilic difluoromethylation was also achieved in the presence of bis(cinchona) alkaloids.