Enantioselective Synthesis of alpha-Amidoboronates Catalyzed by Planar-Chiral NHC-Cu(I) Complexes

The first highly selective catalytic hydroboration of alkyl-substituted aldimines to provide medicinally relevant alpha-amidoboronates is disclosed. The Cu(I)-catalyzed borylation proceeds with excellent facial selectivity when a set of planar-chiral N-heterocyclic carbenes (NHCs) were employed as ligands. Density functional theory computations suggest that interactions between BPin and the planar-chiral catalyst are responsible for the observed stereoselectivity. Important pharmacophores, such as the boronate analogue of isoleucine, can be prepared using a chromatography-free protocol starting from commercially available reagents. The application of these NHC ligands in these Cu(I)-catalyzed processes offers a significant contribution to existing strategies for laboratory-scale preparation of enantioenriched alpha-amidoboronates.