Asymmetric Strecker Reaction of Aldimines Using Aqueous Potassium Cyanide by Phase-Transfer Catalysis of Chiral Quaternary Ammonium Salts with a Tetranaphthyl Backbone

The phase-transfer-catalyzed, highly enantioselective cyanation of aldimines using aqueous KCN has been realized based on the molecular design of chiral quaternary ammonium iodide 2c bearing a stereochemically defined tetranaphthyl backbone. For example, vigorous stirring of a mixture of cyclohexanecarboxaldimine (R = c-Hex) and (R,R,R)-2c (1 mol %) in toluene−KCN aqueous solution (1.5 equiv) at 0 °C for 2 h gave rise to the corresponding protected amino nitrile (R = c-Hex) in 89% yield with 95% ee. A wide range of aliphatic aldimines, including those having α-tert-alkyl substituents, is tolerated by the present system. This study represents a novel approach for the asymmetric Strecker-type reactions, which utilizes chiral phase-transfer catalysts for practical access to various unusual, optically pure α-amino acids.