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Issue 10, 2019
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Convenient access to 5-membered cyclic iminium ions: evidence for a stepwise [4 + 2] cycloaddition mechanism

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Abstract

In situ generation and reaction of novel 5-membered N-tosyl cyclic α,β-unsaturated iminium ions from readily prepared stable precursors is demonstrated. Formal iminium Diels–Alder cycloaddition proceeded in good yield via a stepwise rather than concerted cycloaddition process, confirmed through the isolation of a Mukaiyama–Michael type intermediate. Relative stereochemistry was determined upon subsequent intramolecular cyclisation under Lewis acid catalysis to afford formal endo 5,6-spirobicyclic adducts, as confirmed by crystallography. Further synthetic elaboration towards complex molecular scaffolds based on the dinoflagellate metabolite portimine, a potent apoptosis inducer, were also developed.

Graphical abstract: Convenient access to 5-membered cyclic iminium ions: evidence for a stepwise [4 + 2] cycloaddition mechanism

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Supplementary files

Article information


Submitted
01 Feb 2019
Accepted
08 Feb 2019
First published
11 Feb 2019

Org. Biomol. Chem., 2019,17, 2705-2714
Article type
Paper

Convenient access to 5-membered cyclic iminium ions: evidence for a stepwise [4 + 2] cycloaddition mechanism

J. L. Freeman, M. A. Brimble and D. P. Furkert, Org. Biomol. Chem., 2019, 17, 2705
DOI: 10.1039/C9OB00262F

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