Electrocatalytic redox neutral [3+2] annulation of N-cyclopropylanilines and alkenes

by Wang, Qi; Wang, Qile; Zhang, Yuexiang; Mohamed, Yasmine M.; Pacheco, Carlos; Zheng, Nan; Zare, Richard N.; Chen, Hao

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Although synthetic organic electrochemistry (EC) has advanced significantly, net redox neutral electrosynthesis is quite rare. Two approaches have been employed to achieve this type of electrosynthesis. One relies on turnover of the product by the reactant in a chain mechanism. The other involves both oxidation on the anode and reduction on the cathode in which the radical cation or the radical anion of the product has to migrate between two electrodes. Herein, a home-built electrochemistry/mass spectrometry (EC/MS) platform was used to generate an N-cyclopropylaniline radical cation electrochemically and to monitor its reactivity toward alkenes by mass spectrometry (MS), which led to the discovery of a new redox neutral reaction of intermolecular [3 + 2] annulation of N-cyclopropylanilines and alkenes to provide an aniline-substituted 5-membered carbocycle via direct electrolysis (yield up to 81%). A chain mechanism, involving the regeneration of the substrate radical cation and the formation of the neutral product, is shown to be responsible for promoting such a redox neutral annulation reaction, as supported by experimental evidence of EC/MS.

Journal
Chemical Science
Volume
12
Issue
3
Year
2021
Start Page
969
ISBN/ISSN
2155-5435
DOI
10.1039/d0sc05665k