Electrochemical Azidooxygenation of Alkenes Mediated by a TEMPO-N_3 Charge-Transfer Complex

摘要

We report a mild and efficient electrochemical protocol to access a variety of vicinally C-O and C-N difunctionalized compounds from simple alkenes. Detailed mechanistic studies revealed a distinct reaction pathway from those previously reported for TEMPO-mediated reactions. In this mechanism, electrochemically generated oxoammonium ion facilitates the formation of azidyl radical via a charge-transfer complex with azide, TEMPO-N-3. DFT calculations together with spectroscopic characterization provided a tentative structural assignment of this charge-transfer complex. Kinetic and kinetic isotopic effect studies revealed that reversible dissociation of TEMPO-N-3 into TEMPO center dot and azidyl precedes the addition of these radicals across the alkene in the rate-determining step. The resulting azidooxygenated product could then be easily manipulated for further synthetic elaborations. The discovery of this new reaction pathway mediated by the TEMPO+/TEMPO(center dot )redox couple may expand the scope of aminoxyl radical chemistry in synthetic contexts.