Carba-methylephedrine and carba-pseudo-methylephedrine as tools for probing the role of the nitrogen atom of chiral amino alcohols in asymmetric synthesis

As part of our on-going program on the use of chiral alkoxides as chiral ba ses in asymmetric synthesis, we report that carba-ephedrine analogues of N- methylephedrines, with a simple change of bridging nitrogen for CH, served to probe the role of the nitrogen atom in the discrimination of enantiotopi c protons by means of the derived alkoxides. We suggest reasons why in the pseudo ephedrine series the asymmetric induction is retained while in the e phedrine series the enantioselectivity is strongly affected.