Organocatalytic Enantioselective Friedel−Crafts Alkylation of 4,7-Dihydroindoles with α,β-Unsaturated Aldehydes: An Easy Access to 2-Substituted Indoles

An enantioselective Friedel−Crafts alkylation of 4,7-dihydroindoles and α,β-unsaturated aldehydes has been developed. The process is promoted by diphenylprolinol ether to afford 2-substituted 4,7-dihydroindoles in high yields and enantioselectivities. After a subsequent oxidation of the products, the optically active 2-substituted indoles could be obtained smoothly in high yields without any loss of enantioselectivity.