Fang Huaquan, Manoj Niket, Popescu Mihai V, Noble Adam, Paton Robert S, Aggarwal Varinder K
School of Chemistry, University of Bristol, Cantock's Close, BS8 1TS, Bristol, UK.
Department of Chemistry, Colorado State University, 80523-1872, Ft. Collins, Colorado, US.
Angew Chem Int Ed Engl. 2025 Jan 2;64(1):e202413504. doi: 10.1002/anie.202413504. Epub 2024 Nov 6.
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 the 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.
末端烯烃的不对称双硼化反应已得到充分确立，随后通常可实现对空间位阻较小的伯硼酸酯进行选择性官能团化。相反，对空间位阻较大的仲硼酸酯进行选择性官能团化仍然具有挑战性。控制双（硼）化合物化学选择性官能团化的另一种方法是使两个硼基部分具有不同的路易斯酸性，因为此时反应活性将由路易斯酸性而非空间位阻决定。我们在此报告了用（频哪醇）B - B（联萘酚）在铂催化下对未活化烯烃进行区域和对映选择性双硼化反应。多种末端烯烃和环状烯烃都能发生双硼化反应，生成具有高水平区域和对映选择性控制的可区分的1,2 - 双（硼）化合物，从而能从一个常见中间体获得多种新型结构单元。该反应将路易斯酸性较弱的B（联萘酚）基团置于空间位阻较小的位置，所得的1,2 - 双硼基烷烃会发生位于空间位阻较大位置的B（频哪醇）基团的选择性转化。通过密度泛函理论计算研究了双硼化反应的区域选择性，据信其源于反位效应，这种效应降低了在铂配合物中使较弱电子给体[B（频哪醇）与B（联萘酚）]与强电子给体（烷基）相对的区域异构体形成的活化能垒。
