Friedel–crafts alkylations of indoles, furans, and thiophenes with arylmethyl acetates promoted by trimethylsilyl trifluoromethanesulfonate

Abstract

Various indoles undergo Friedel–Crafts alkylation at the 3-position when treated with secondary arylmethyl acetates in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) and 2,6-lutidine. Tertiary benzylic alcohols are also effective alkylating agents, undergoing TMSOTf-promoted activation to yield alkylated indoles that feature quaternary centers. A related study shows that benzofuran reacts under similar conditions to yield 2-alkylated benzofurans when treated with similar alkylating agents, and the reaction has been extended to include other representative heteroarenes. Yields for these Friedel–Crafts alkylation products range from 43%–99% over a wide range of substrate combinations.