Catalytic Asymmetric Synthesis of a Nitrogen Analogue of Dialkyl Tartrate by Direct Mannich Reaction under Phase-Transfer Conditions

Phase-transfer-catalyzed direct Mannich reaction of glycinate Schiff base <b>3</b> with α-imino ester <b>4</b> has been accomplished with high enantioselectivity by the utilization of <i>N</i>-spiro <i>C</i>₂-symmetric chiral quaternary ammonium bromide <b>2</b> as a catalyst. This methodology enables the catalytic asymmetric synthesis of differentially protected 3-aminoaspartate, a nitrogen analogue of dialkyl tartrate. The product (<i>syn</i>-<b>5</b>) was converted into a precursor (<b>6</b>) of streptolidine lactam.