ChemInform Abstract: The Broensted Acid Catalyzed, Enantioselective Vinylogous Mannich Reaction.

Abstract

The Broensted Acid Catalyzed, Enantioselective Vinylogous Mannich Reaction.-The three-component Mannich reaction of aromatic, heteroaromatic, or aliphatic aldehydes with amine (II) and silyl dienolate (III) (Z:E=2.5:1) in the presence of the optimized axially chiral phosphoric acid diester PHA provides δ-amino α,β-unsubstituted esters (IV) and (VI). The protic reaction medium is found to be optimal to trap the formed cationic silicon species as silanol. Silyl dienolate (VIII) (1E:1Z=1:1.5) undergoes a two-component Mannich reaction with aromatic or heteroaromatic imines to give under similar conditions products bearing two stereogenic centers. Whereas the geometry of the double bond directly attached to the acetal moiety of the dienolate has no effect on the stereochemical outcome, the geometry of the attached propenyl group significantly influences the yield and stereoselectivity. The (3Z)-analogue of compound (VIII) furnishes only low yields and stereoselectivities. -(SICKERT, M.; ABELS, F.; LANG, M.; SIELER, J.; BIRKEMEYER, C.; SCHNEIDER*, C.; Chem.