Bismuth Triflate Catalyzed Condensation of Indoles with Acetone

Reaction of different substituted indoles with acetone was investigated using Bi(OTf)3 as a catalyst. An efficient protocol was developed for the synthesis of spiro indoles, 1-methyl-cyclopenta[b]indole and bis(1-methyl-1H-indolyl)propanes via the reaction of indole with acetone in the presence of Bi(OTf)3. The reaction conditions were benign, required shorter reaction time, and gave good yields.