A practical synthesis of 3-indolyl α,β-unsaturated carbonyl compounds

An acid-catalyzed practical synthesis of 3-indolyl α,β-unsaturated carbonyl compounds using methyl 3-methoxyacrylate, methyl 3,3-dimethoxypropionate, or 1,1-dimethoxy-3-butanone is reported. 35% HCl aqueous solution catalyzes this reaction efficiently in acetic acid. One of the most favorable substrates is 3-(4-fluorophenyl)-1-isopropyl-1H-indole, which reacts nearly quantitatively to give the corresponding α,β-unsaturated ester, and the scope of the reaction can be extended to some electron-rich benzene derivatives.