Structurally Well-Defined, Recoverable <i>C</i>₃-Symmetric Tris(β-hydroxy phosphoramide)-Catalyzed Enantioselective Borane Reduction of Ketones

A series of new chiral C3-symmetric tris(β-hydroxy phosphoramide) ligands have been synthesized via the reaction of trisphosphoramide ester and Grignard reagents. The catalytic asymmetric borane reduction of ketones with these new C3-symmetric chiral tris(β-hydroxy phosphoramide)s was investigated. Structurally well-defined, recoverable ligand 1d is an efficient catalyst for the enantioselective borane reduction of both electron-deficient and electron-rich ketones, and high enantioselectivities were achieved (up to 98% ee).