A Practical Synthetic Approach to Chiral (α-Chloroalkyl)boronic Esters via Iridium-Catalyzed Chemoselective Hydrogenation of Chloro-Substituted Alkenyl Boronates

Abstract

Chiral (α-chloroalkyl)boronic esters are obtained by homogeneous asymmetric iridium-catalyzed chemoselective hydrogenation of (1-chloro-1-alkenyl)boronic esters. P,N–Iridium catalysis provides low level of dehalogenation during the hydrogenation, while the catalyst activity and enantioselectivity essentially depends on the applied P,N ligand features. Fine tuning of P,N ligand structures enables high conversions, broad substrate acceptance, and high to excellent enantioselectivities with enantiomeric excess values up to 94% along with low levels of dechlorination. Low catalyst loading with S/C = 200 can also be achieved for the preparation of an industrially important isobutyl derivative.