Synthesis of 1-(β-coumarinyl)-1-(β-indolyl)trifluoroethanols through regioselective Friedel–Crafts alkylation of indoles with β-(trifluoroacetyl)coumarins catalyzed by Sc(OTf)3

Abstract

A highly efficient Friedel–Crafts alkylation of indole derivatives with β-(trifluoroacetyl)coumarins using Sc(OTf)₃ as a catalyst has been developed, which gives regioselective 1,2-adducts to afford 1-(β-coumarinyl)-1-(β-indolyl)trifluoroethanols. A series of tertiary trifluoroethanols containing different indole and coumarin groups were synthesized in moderate to excellent yields (up to 95%) in the presence of 5 mol% catalyst in a short time (only 2 minutes at least). A mechanism of the reaction, in which the trace amount of water plays the role of proton transfer in catalyzing circulation was proposed and confirmed.