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Issue 9, 2017
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Enantioselective synthesis of spiro γ-butyrolactones by N-heterocyclic carbene (NHC)-catalyzed formal [3 + 2] annulation of enals with 3-hydroxy oxindoles

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Abstract

The N-heterocyclic carbene (NHC)-catalyzed enantioselective formal [3 + 2] annulation of α,β-unsaturated aldehydes with 3-hydroxy oxindoles is presented. Under oxidative conditions using the bisquinone oxidant, the reaction resulted in the synthesis of spiro γ-butyrolactones in moderate to good yields, enantioselectivity and diastereoselectivity. The reaction likely proceeds via the generation of the NHC-bound α,β-unsaturated acylazolium intermediate from enals, which was intercepted by the dioxindoles in a formal [3 + 2] pathway to form the spirocyclic compounds. However, a deeper mechanistic investigation revealed that the reaction can also proceed via the homoenolate intermediate. In this case, the dioxindole was oxidized to the corresponding isatin derivative using traces of air under basic conditions, and was intercepted with the NHC-bound homoenolate intermediate in a formal [3 + 2] pathway to afford the spiro compound.

Graphical abstract: Enantioselective synthesis of spiro γ-butyrolactones by N-heterocyclic carbene (NHC)-catalyzed formal [3 + 2] annulation of enals with 3-hydroxy oxindoles

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Publication details

The article was received on 19 Jan 2017, accepted on 07 Feb 2017 and first published on 07 Feb 2017


Article type: Paper
DOI: 10.1039/C7OB00148G
Citation: Org. Biomol. Chem., 2017,15, 2013-2019
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    Enantioselective synthesis of spiro γ-butyrolactones by N-heterocyclic carbene (NHC)-catalyzed formal [3 + 2] annulation of enals with 3-hydroxy oxindoles

    S. Mukherjee, S. Joseph, A. Bhunia, R. G. Gonnade, S. R. Yetra and A. T. Biju, Org. Biomol. Chem., 2017, 15, 2013
    DOI: 10.1039/C7OB00148G

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