Enantioselective addition of arylboronic acids to aldimines catalyzed by rhodium-bispnosphoramidide complex

摘要

We previously reported that rhodium(I)-O-linked bisphosphoramidite (Me-BIPAM), which was synthsized from O-linked BINOL, complex is an excellent catalyst for enantioselective 1,4-addition of arylboronic acids to unsaturated cyclic and acyclic carbonyl compounds. To enlarge coverage of this ligand, we examined rhodium catalyzed asymmetric addition of arylboronic acids for N-tosylaldimines. However the moderate enantioselectivity was obtained from the addition of 4-MeOC6H4CHNTs with PhB(OH)2 by rhodium/Me-BIPAM (83%, 74%ee). Herein we report that a new bidentate phosphoramidite (N-Me-BIPAM) synthesized based on N-linked BINOL. This ligand was found to be highly effective for rhodium-catalyzed asymmetric addition of arylboronic acids for aldimines. The addition of N-tosyl and N-nosylaldimines for arylboronic acids resulted in good enantioselectivities by rhodium/N-Me-BIPAM complex (Scheme 1).