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

A highly efficient Friedel-Crafts alkylation of indole derivatives with beta-(trifluoroacetyl)coumarins using Sc(OTf)(3) as a catalyst has been developed, which gives regioselective 1,2-adducts to afford 1-(beta-coumarinyl)-1-(beta-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.