NHC-catalysed enantioselective intramolecular formal [4+2] cycloadditions using carboxylic acids as azolium enolate precursors

TETRAHEDRON

卷:76

Article

Attaba, Nassilia¹  Smith, Andrew D.¹ 

[1] Univ St Andrews, Sch Chem, EaStCHEM, St Andrews KY16 9ST, Fife, Scotland

关键词: NHC;    Enantioselective catalysis;    [4+2] cycloaddition;    Carboxylic acid;    Yamaguchi reagent;   

DOI  :  10.1016/j.tet.2019.130835

来源: Elsevier

【 摘 要 】

An NHC-catalysed intramolecular formal [4 + 2] cycloaddition protocol using carboxylic acid starting materials containing a tethered enone is reported. Optimisation studies using a model substrate showed that the use of the Yamaguchi reagent (2,4,6-trichlorobenzoyl chloride) for in situ preparation of a mixed anhydride was necessary for effective catalysis, leading to highest product yield and stereoselectivity. Using this protocol, a range of dihydrobenzofurans were accessed in moderate to high yield, and with high to excellent diastereo- and enantioselectivity (up to > 95:5 dr and > 99:1 er). This methodology was extended to the synthesis of syn-dihydrochromenone and syn-dihydropyranone derivatives in moderate to high yield and with excellent diastereo- and enantioselectivity. (C) 2019 Published by Elsevier Ltd.

【 授权许可】

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