Polymer-supported acylhydrazones. Use in Sc(OTf)3-catalyzed Mannich-type reactions providing an efficient method for the preparation of diverse pyrazolone derivatives
摘要:
Polymer-supported acylhydrazones, prepared from polystyrene resin (1%-divinylbenzene), reacted with ketene silyl acetals in the presence of a catalytic amount of scandium triflate (Sc(OTf)(3)), to afford the corresponding beta-hydrazinoesters, which were cyclized and cleaved from the support simultaneously by treatment with a base to produce diverse pyrazolone derivatives. (C) 1999 Elsevier Science Ltd. All rights reserved.
The alpha-hydroxy-alpha-methyl-beta-hydroxy units are enantioselectively prepared by way of asymmetric aldol reactions between both achiral beta,beta-disubstituted silyl enolates and aldehydes. (-)-2-C-Methyl-D-threono-1,4-lactone is conveniently synthesized by using this reaction.