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

Abstract

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 H₂O 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.