One-pot Construction of Multi-stereocenters Utilizing Tandem Michael-aldol Reaction

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1. Development of a new Michael-aldol reaction of thiolactams inducing malti-stereocenters : Reaction of N-cinnamoyl-oxazolidine-2-thione bearing a chiral center at the 4-or 5-position with an aldehyde was studied in the presence of a Lewis acid. A tricyclic compound with four new stereocenters was formed in a high chemical yield with a high diastereoselectivity.. Acetals diastereoselectively gave 2-(α-sulfanylbenzyl)-3-methoxypropionic acids in a high chemical yields. In the reactions the Lewis acid played both roles of an activator of enones and a generator of carbocations. The Lewis acid controlled the stereoselectivity of the Michael addition of the thione to an enone.2. Chemical transformation and utilization of the chiral Micheal-aldol products : The tricyclic compounds obtained from aldehydes were led to 1-phenyl-2-methylsulfanyl-1,3-propanediols possessing three consecutive chiral centers via acid hydrolysis, S-methylation and reduction. The Michael-aldol adducts derived from acetals were transformed into 2-(α-alkoxybenzyl)-3-sulfanylpropanols by the reductive removal of the chiral auxiliary. The chiral S-Acyl3-sulfanylpropanols acylated amines in high chemical yields, but the enantioselectivity of the reaction was very low.3. Intermolecular asymmetric Michael-aldol reactions using chiral cyclic thiocarbamates or thioureas : Several new cyclic thiocarbamates or thioureas were prepared and used for the asymmetric reactions of enones with aldehydes. The reactions proceeded more smoothly than the conventional ones but stereoselectivity of the reaction was low.We developed the asymmetric intramolecular Michael-aldol reactions of N-enoyl-oxazolidine・or thiazolidine-2-thiones with aldehydes or acetals in the presence of a Lewis acid and synthesized 1-phenyl-2-methylsulfanyl-1,3-propanediols or 2-(α-alkoxybenzyl)-3-sulfanylpropanols possessing three consecutive chiral centers.