CATALYTIC ACTIVATION OF IMINE DERIVATIVES USING NOVEL LEWIS-ACIDS

The Lewis acid-mediated reactions of imine are one of the most powerfu l methods for preparation of nitrogen-containing compounds. However, t here are few examples of the reactions using catalytic amounts of Lewi s acids, because the strong coordination of the products (which are mo stly secondly or tertiary amines), deactivates the acids. This article introduces several types of new achiral and chiral Lewis acids which can mediated the reactions of imines catalytically. The essence of the catalytic activation of imines by Lewis acids is the equilibrium betw een Lewis acids and bases (imines or products), and it has been reveal ed that rare earth triflates (lanthanide and scandium trifluoromethane sulfonate) are excellent catalysts for this purpose. Imino-aldol react ions, aza Diels-Alder reactions, allylation reactions, cyanation react ions, and three-component reactions of aldehydes, amines, and nucleoph iles were successfully carried out in the presence of catalytic amount s of rare earth triflates. Polymer-supported reagents also worked well by using the triflates as catalysts. In addition, it was shown that g roup IV triflates (Zr and Hi triflates) were effective for catalytic a ctivation of imines. The first truly catalytic asymmetric reactions of imines have been achieved using new chiral Lewis acids. In the presen ce of a catalytic amount of a chiral rare earth catalyst, imines deriv ed from 2-aminophenol and aldehydes reacted with cyclopentadiene or vi nyl ethers to afford 8-hydroxytetrahydroquinoline derivatives in high yields with high diastereo-and enantioselectivities. Moreover, the fir st catalytic enantioselective Mannich-type reactions of imines with si lyl enolates using a novel chiral zirconium catalyst have been develop ed.High levels of enantioselectivities in the synthesis of chiral beta -amino ester derivatives, beta-amino alcohol derivatives, and tetrahyd ropyridine derivatives have been achieved using these reactions.