Leung VMY, Wong HCF, Pook CM, Tse YLS, Yeung YY. Trialkylphosphonium oxoborates as C(sp
3)-H oxyanion holes and their application in catalytic chemoselective acetalization.
Chem Sci 2023;
14:12684-12692. [PMID:
38020391 PMCID:
PMC10646966 DOI:
10.1039/d3sc03081d]
[Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Accepted: 10/15/2023] [Indexed: 12/01/2023] Open
Abstract
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(sp3)-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(sp3)-Hs that serve as a mimic of oxyanion holes, which can stabilize the oxyanion intermediates via multiple C(sp3)-H non-classical hydrogen bond interactions.
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