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

The first highly selective catalytic
hydroboration of alkyl-substituted
aldimines to provide medicinally relevant α-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 α-amidoboronates.