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

• Published in: Angewandte Chemie Vol. 128; no. 34; pp. 10123 - 10127
• Main Authors: Zhu, Qilei, Gentry, Emily C., Knowles, Robert R.
• Format: Journal Article
• Language: English; German
• Published: Weinheim Blackwell Publishing Ltd 16.08.2016; Wiley Subscription Services, Inc
• Subjects: Alkoxyamine; Bonding strength; Carbokationen; Catalysis; Catalysts; Cations; Chemistry; Cleavage; Mesolyse; Nucleophiles; Photoredoxkatalyse; Radicals; Radikalkationen; Scission
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.201604619

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. Carbokation‐Zwischenstufen sind durch Mesolyse von Alkoxyamin‐Radikalkationen mit einer erstaunlich schwachen C‐O‐Bindung zugänglich. Bei der spontanen Bindungsspaltung entstehen das stabile Nitroxylradikal TEMPO. und die reaktive Carbokation‐Zwischenstufe, die anschließend von verschiedenen Nukleophilen abgefangen werden kann.