Enantioselective Syntheses of Secondary Alkylboronates via Asymmetric Regioselective Reduction of 1,3‐Dienylboronates

We report herein the development of catalytic asymmetric synthesis of secondary alkylboronates. Under the optimal conditions, Cu‐catalyzed semi‐reduction of 1‐alkyl‐ or 1,3‐dialkyl‐substituted 1‐boryl‐1,3‐butadienes forms secondary alkylboronates with excellent regioselectivities and enantioselectivities. With H 2 O as the source of hydrogen, the reaction proceeds through a protoboration and protodeboration cascade reaction sequence to generate the desired boronates. By using a slightly modified protocol, the process allows for access to enantioenriched deuterium‐labeled secondary alkylboronates. Density functional theory (DFT) studies were conducted to probe the origins of selectivities.