Catalytic enantioselective addition of propionate units to imines: an efficient synthesis of anti-alpha-methyl-beta-amino acid derivatives

Optically active anti-alpha-methyl-beta-amino acid derivatives have been prepared based on catalytic enantioselective addition of propionate units to simple and inert imines using a chiral zirconium complex. High reactivity and selectivity with wide substrate scope were attained by using a new chiral ligand, (R)-6,6'-bis(pentafluoroethyl)-1,1'-bi-2-naphthol ((R)-6,6'-C(2)F(5)BINOL). The reactions using geometrically isomeric ketene silyl acetals gave excellent anti-selectivity with high enantiomeric excess in both cases. Synthetic utility of this reaction has been demonstrated by the preparation of various anti-alpha-methyl-beta-amino acid and trans-3,4-disubstituted beta-lactam derivatives.