THE KINETIC ANOMERIC EFFECT - ADDITIONS OF NUCLEOPHILES AND OF DIPOLAROPHILES TO N-GLYCOSYLNITRONES AND TO N-PSEUDOGLYCOSYLNITRONES

To prove the hypothesis of the role of a kinetic anomeric effect in the highly diastereoselective additions of nucleophiles and of dipolarophiles to N-glycosylnitrones we compared these additions to those to analogous N-pseudoglycosylnitrones having a methylene group in place of the furan ring oxygen. An almost complete loss of the diastereoselectivity was found for the addition of lithium dimethyl phosphite tris(trimethylsilyl)phosphite and methyl methacrylate to the N-pseudoglycosylnitrones which moreover reacted more slowly as predicted by the hypothesis of the kinetic anomeric effect. Pseudo first order kinetics for the ZnCl2 promoted addition of P(OSiMe3)3 to nitrones were measured; activation energies diastereoselectivities and the influence of Lewis acids are discussed. © 1990.