Highly Diastereoselective Catalytic Meerwein−Ponndorf−Verley Reductions

[GRAPHICS] Very practical synthesis of ephedrine analogues in high yields and enantiopurity was realized by a highly diastereoselective Meerwein-Ponndorf-Verley (MPV) reduction of protected alpha-amino aromatic ketones using catalytic aluminum isopropoxide. The high anti selectivity resulted from the chelation of the nitrogen anion to the aluminum. In contrast, high syn selectivity was obtained with alpha-alkoxy ketones and other compounds via Felkin-Ahn control.