Aminocatalytic enantioselective 1,6 additions of alkyl thiols to cyclic dienones: Vinylogous iminium ion activation

In the presence of chiral amines, 2,4-dienones are activated toward the attack of a nucleophile at the δ?position, a mode of activation that is termed vinylogous iminium?ion catalysis. Specifically, the 1,6?addition of alkyl thiols to β-substituted cyclic dienones was catalyzed by a cinchona-based primary amine; the reaction was highly stereoselective and displayed high selectivity for reaction at the δ?position.