Platinum-catalyzed regio- and enantioselective diboration of unactivated alkenes with (pin)B-B(dan).

Abstract

Asymmetric diboration of terminal alkenes is well established, and subsequent selective functionalization of the less hindered primary boronic ester is commonly achieved. Conversely, selective functionalization of the sterically less accessible secondary boronic ester remains challenging. An alternative way to control chemoselective functionalization of bis(boron) compounds is by engendering different Lewis acidity to the two boryl moieties, since reactivity would then be dictated by Lewis acidity instead of sterics. We report herein the regio- and enantioselective Pt-catalyzed diboration of unactivated alkenes with (pin)B-B(dan). A broad range of terminal and cyclic alkenes undergo diboration to furnish the differentiable 1,2-bis(boron) compounds with high levels of regio- and enantiocontrol, giving access to a wide variety of novel building blocks from a common intermediate. The reaction places the less Lewis acidic B(dan) group at the less hindered position and the resulting 1,2-bisboryl alkanes undergo selective transformations of the B(pin) group located at the more hindered position. The regioselectivity of diboration has been studied by DFT calculations and is believed to originate from the trans influence, which lowers the activation barrier for formation of the regioisomer that places the weaker electron donor [B(pin) vs B(dan)] opposite the strong electron donor (alkyl group) in the platinum complex.