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. 2016 Aug 16;55(34):9969-73.
doi: 10.1002/anie.201604619. Epub 2016 Jul 12.

Catalytic Carbocation Generation Enabled by the Mesolytic Cleavage of Alkoxyamine Radical Cations

Qilei Zhu  1 , Emily C Gentry  1 , Robert R Knowles  2
Affiliations

Catalytic Carbocation Generation Enabled by the Mesolytic Cleavage of Alkoxyamine Radical Cations

Qilei Zhu et al. Angew Chem Int Ed Engl. .

Abstract

A new catalytic method is described to access carbocation intermediates via the mesolytic cleavage of alkoxyamine radical cations. In this process, electron transfer between an excited state oxidant and a TEMPO-derived alkoxyamine substrate gives rise to a radical cation with a remarkably weak C-O bond. Spontaneous scission results in the formation of the stable nitroxyl radical TEMPO(.) as well as a reactive carbocation intermediate that can be intercepted by a wide range of nucleophiles. Notably, this process occurs under neutral conditions and at comparatively mild potentials, enabling catalytic cation generation in the presence of both acid sensitive and easily oxidized nucleophilic partners.

Keywords: alkoxyamines; carbocations; mesolytic cleavage; photoredox catalysis; radical cations.

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Figures

Scheme 1
Scheme 1
Reaction design and thermochemistry of bond weakening in radical cations. BDFE = bond dissociation free energy in kcal/mol.
Scheme 2
Scheme 2. Proposed catalytic cycle
See this image and copyright information in PMC

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