Structurally well-defined, recoverable C₃-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).