Intramolecular chiral relay at stereogenic nitrogen: oxazolidine catalysts derived from Ephedra alkaloids

A series of oxazolidines have been prepared by reaction of either (1R,2S)-ephedrine or (1S,2S)-pseudoephedrine with salicylaldehyde derivatives. The resultant oxazolidines were used as catalytic ligands in the addition of diethylzinc to a variety of aromatic and aliphatic aldehydes. It was determined that the (1R,2S)-ephedrine based oxazolidine derivative 9 gave the highest enantioselectivities.