Diastereoselective reduction of α-aminoketones:: Synthesis of anti- and syn-β-aminoalcohols

Reduction of N-t-BOC-protected-N-alkyl alpha-aminoketones with LiEt3BH or Li(s-Bu)(3)BH furnishes protected syn-beta-aminoalcohols with high selectivities. In contrast, removal of the BOC group followed by reduction of the aminoketone gives anti-beta-aminoalcohols with variable selectivities. With aromatic ketones, selectivities are typically high while aliphatic ketones show mediocre to high selectivities depending on steric considerations.