Chalcogenide–Lewis Acid Mediated Tandem Michael Aldol Reaction — an Alternative to the Morita–Baylis–Hillman Reaction and a New Development

A tandem Michael aldol reaction mediated by a chalcogenide and Lewis acid was developed in three different types. Reactions of electron‐deficient alkenes with aldehydes or α‐keto esters in the presence of a sulfide and TiCl 4 gave α‐chloromethyl aldols. Reactions of chalcogenide–enones with carbonyl compounds gave α‐(α‐hydroxyalkyl)enones (Mori‐ta–Baylis–Hillman adducts) after the work‐up of the reaction mixture with triethylamine. The intramolecular Michael aldol reactions of N ‐enoylthioamides with aldehydes in the presence of BF 3 Et 2 O produced tricyclic compounds bearing a bridgehead bound to four heteroatoms and induced four stereocenters in one step, three of which were consecutive. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)