NHC-catalysed enantioselectiveintramolecular formal [4+2] cycloadditions using carboxylic acids as azolium enolate precursors
Abstract
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.
Citation
Attaba , N & Smith , A D 2019 , ' NHC-catalysed enantioselectiveintramolecular formal [4+2] cycloadditions using carboxylic acids as azolium enolate precursors ' , Tetrahedron , vol. In press . https://doi.org/10.1016/j.tet.2019.130835
Publication
Tetrahedron
Status
Peer reviewed
ISSN
0040-4020Type
Journal article
Description
We thank the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013) ERC grant agreement no 279850 (NA) and the Royal Society (Wolfson Merit Award to ADS).Collections
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