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Asymmetric synthesis of spiro-structural 2,3-dihydrobenzofurans via the bifunctional phosphonium salt-promoted [4 + 1] cyclization of ortho-quinone methides with α-bromoketones

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Abstract

We report a practical and scalable method for the highly diastereo- and enantio-selective construction of 2,3-dihydrobenzofurans bearing spiro-structures by means of cyclization reactions between ortho-quinone methides and α-bromoketones through bifunctional phosphonium salt catalysis under mild conditions. A variety of spiro-fused 2,3-dihydrobenzofuran derivatives were readily synthesized in high yields with excellent diastereo- and enantio-selectivities (up to >20 : 1 dr and 97% ee). This protocol represents an alternative facile way for preparing biologically important chiral 2,3-dihydrobenzofurans. Moreover, mechanistic observations indicated that the hydrogen bonding interaction between the Brønsted acid moiety of the phosphonium catalyst and the “C[double bond, length as m-dash]O” unit of the quinone is crucial for stereoinduction.

Graphical abstract: Asymmetric synthesis of spiro-structural 2,3-dihydrobenzofurans via the bifunctional phosphonium salt-promoted [4 + 1] cyclization of ortho-quinone methides with α-bromoketones

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Publication details

The article was received on 07 Sep 2019, accepted on 02 Oct 2019 and first published on 08 Oct 2019


Article type: Research Article
DOI: 10.1039/C9QO01096C
Org. Chem. Front., 2019, Advance Article

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    Asymmetric synthesis of spiro-structural 2,3-dihydrobenzofurans via the bifunctional phosphonium salt-promoted [4 + 1] cyclization of ortho-quinone methides with α-bromoketones

    S. Zhang, X. Yu, J. Pan, C. Jiang, H. Zhang and T. Wang, Org. Chem. Front., 2019, Advance Article , DOI: 10.1039/C9QO01096C

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