Stereoselective Dehydroxyboration of Allylic Alcohols to Access (E)-Allylboronates by a Combination of C–OH Cleavage and Boron Transfer under Iron Catalysis

Abstract

Iron-catalyzed direct SN2′ dehydroxyboration of allylic alcohols has been developed to access (E)-stereoselective allylboronates. Allylic alcohols with diverse structures and functional groups, especially derived from natural products, underwent smooth transformation. The six-membered ring transition state formed by allylic alcohols and iron–boron intermediate was indicated to be the key component involved in transfer of the boron group, activation of the C–OH bond, and control of the stereoselectivity.

LiOtBu-Promoted trans-Stereoselective and β-Regioselective Hydroboration of Propargyl Alcohols

“…β-Bpin-substituted ( E )-allylic alcohols were versatile building blocks, which can proceed manifold transformations of all of the −Bpin, alkenyl, and −OH groups. − However, these compounds need to be synthesized from alkynylboronates via hydroboration, transmetalation, and then nucleophilic addition to aldehydes, which not only requires multi-step synthesis with the sensitive reagents Cy 2 BH and ZnMe 2 but is also limited to obtaining internal secondary allylic alcohols (Scheme b). As a concise approach for obtaining β-Bpin-substituted ( E )-allylic alcohols, here, we report a trans -stereoselective and β-regioselective hydroboration of propargyl alcohols merely with (Bpin) 2 as the boron reagent and LiO t Bu as the base in dimethyl sulfoxide (DMSO) solution at room temperature (Scheme c). , Both internal and terminal, secondary, and tertiary β-Bpin-substituted ( E )-allylic alcohols could be prepared from a variety of propargyl alcohols in one step.…”