Electrocatalytic redox neutral [3 + 2] annulation of N-cyclopropylanilines and alkenes |
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Authors: | Qi Wang Qile Wang Yuexiang Zhang Yasmine M. Mohamed Carlos Pacheco Nan Zheng Richard N. Zare Hao Chen |
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Affiliation: | Department of Chemistry & Environmental Science, New Jersey Institute of Technology, Newark New Jersey 07102 USA.; Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville Arkansas 72701 USA.; Department of Chemistry and Biochemistry, Ohio University, Athens Ohio 45701 USA ; Department of Chemistry, Stanford University, Stanford California 94305-5080 USA, |
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Abstract: | 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.We report the use of an online electrochemistry/mass spectrometry platform to develop a redox neutral electrosynthesis of 5-membered rings via [3 + 2] annulation of N-cyclopropylanilines and alkenes, without additional oxidant, reductant or catalyst. |
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