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

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