C3 versus C5 Regioselectivity in the Intramolecular Dehydrative Friedel-Crafts Alkylation of Indole C4-Tethered Carbinols.

Described herein is a mild catalytic dehydrative Friedel-Crafts alkylation of 1,1-diarylalkanols─a challenging reaction with exceedingly rare previous success, presumably because of the unfavorable steric hindrance around the reactive centers and the competitive E1 reaction. Executing in an intramolecular fashion and benefiting from the high nucleophilicity of indole, we have successfully utilized this reaction in synthesizing 3,4-fused indoles. Interestingly, the Friedel-Crafts alkylation strategy could also be applied to access 4,5-fused indoles via modification of the tether connecting the alcohol and indole moieties.