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

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journal contribution
posted on 13.08.2018, 00:00 by C. Benjamin Schwamb, Keegan P. Fitzpatrick, Alexander C. Brueckner, H. Camille Richardson, Paul H.-Y. Cheong, Karl A. Scheidt
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.