Sulfuric Acid‐Catalyzed Regioselective Alkylation of Indoles and β‐Naphthols with Ketene Dithioacetal‐Based Allylic Alcohols

A novel catalytic alkylation of indoles with allylic alcohols has been developed. Catalyzed by sulfuric acid (10 mol-%), the reaction between indoles 2 and allylic alcohols 1 based on ketene dithioacetal affords polyfunctionalized indoles 3 in good to excellent yields with high regioselectivities under mild conditions. The catalytic carbon-carbon coupling reaction provides a facile method for the environmentally benign functionalization of indoles with the advantages of good regiochemistry, atom efficiency, easily available catalyst, good yields and the synthetic potential of the polyfunctionalized indole products. Thus, further transformation of the resulting indoles 3 into pyridoindolone derivatives 4 was investigated. The efficiency of this carbon-carbon coupling reaction of 1 with 2 under the catalysis of sulfuric acid is due to the efficient formation of the reactive intermediate I, which is a carbocation that is strongly stabilized by two alkylthio groups at the terminal of the carbon-carbon double bond. The extension of this catalytic strategy to the synthesis of β-naphthols 5 was also achieved.