Enantioselective Organocatalytic Michael Addition to Unsaturated Indolyl Ketones.

An efficient enantioselective organocatalytic method for the synthesis of N-alkylated indoles with α-branched alkyl substituents from the corresponding unsaturated indolyl ketones via a Michael addition has been developed. The resulting products were obtained in high enantioselectivities and in good yields. Various nucleophiles (nitroalkanes, malononitrile, malonic esters) can be used. The substitution pattern of the indole ring had no significant impact on the reaction outcome. Both electron-withdrawing and electron-donating substituents in any position of the heteroaromatic ring were well-tolerated.