Leung Vincent Ming-Yau, Wong Hong-Chai Fabio, Pook Chun-Man, Tse Ying-Lung Steve, Yeung Ying-Yeung
Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The Chinese University of Hong Kong Shatin, NT Hong Kong China
Chem Sci. 2023 Oct 20;14(44):12684-12692. doi: 10.1039/d3sc03081d. eCollection 2023 Nov 15.
The use of trialkylphosphonium oxoborates (TOB) as catalysts is reported. The site-isolated borate counter anion in a TOB catalyst increases the availability of C(sp)-H to interact with electron donor substrates. The catalytic protocol is applicable to a wide range of substrates in the acetalization reaction and provides excellent chemoselectivity in the acetalization over thioacetalization in the presence of alcohols and thiols, which is otherwise hard to achieve using typical acid catalysts. Experimental and computational studies revealed that the TOB catalysts have multiple preorganized C(sp)-Hs that serve as a mimic of oxyanion holes, which can stabilize the oxyanion intermediates multiple C(sp)-H non-classical hydrogen bond interactions.
据报道，使用三烷基鏻氧硼酸盐（TOB）作为催化剂。TOB催化剂中位点隔离的硼酸盐抗衡阴离子增加了C(sp)-H与电子供体底物相互作用的可能性。该催化方案适用于缩醛化反应中的多种底物，并在存在醇和硫醇的情况下，在缩醛化反应中相对于硫缩醛化反应提供了优异的化学选择性，而使用典型的酸催化剂则难以实现这一点。实验和计算研究表明，TOB催化剂具有多个预组织的C(sp)-H，可作为氧阴离子空穴的模拟物，通过多个C(sp)-H非经典氢键相互作用来稳定氧阴离子中间体。
