ASYMMETRIC-SYNTHESIS OF EPHEDRINE ANALOGS

Addition of nitromethane to the chiral chromium tricarbonyl complex of o-tolualdehyde (1) gives, under conditions of kinetic control, the nitroalcohol 2 with ∼95% of asymmetric induction. Compound 2 then gives, in 3 steps, the corresponding aminoalcohol in about 40% yield. Use of nitroethane gives the nitroalcohol with a small diastereoselectivity at C(2)-C(3) (d.e. = 30 and 55%), but analogs of ephedrine and pseudoephedrine can be obtained optically pure by chromatography.