Elucidating the Mechanism of Electrooxidative Allene Dioxygenation: Dual Role of Tetramethylpiperidine <i>N</i>-Oxyl (TEMPO)
Ken S. Lee, Federico Barbieri, Emanuele Casali, Elijah T. Marris, Giuseppe Zanoni, Jennifer M. Schomaker
Abstract
The cumulated π system of a nonsymmetric allene contains three distinct unsaturated carbons that imbue it with unique reactivity toward radicals as compared to its alkene and alkyne counterparts. Despite the synthetic potential of these versatile building blocks, electrochemical transformations of allenes have been historically underexplored. Myriad strategies for easy access to allenes, coupled with the resurgence of interest in sustainable oxidative transformations of hydrocarbons, prompted our efforts to conduct an in-depth investigation of a rare example of an electrochemical TEMPO-mediated allene dioxygenation. The resultant vinyl-TEMPO motif is readily postfunctionalized to install a heteroatom at each allene carbon. Mechanistic investigations, including cyclic voltammetry (CV) studies, computations, and monitoring by operando NMR (ReactNMR) were performed to lay the groundwork for future electrochemical allene functionalizations that deliver unique synthetic building blocks.