A versatile electrocatalytic [3+2] ring expansion approach for efficient electrosynthesis of oxa-/aza-heterocyclic compounds

Abstract

Electrosynthesis has emerged as a frontrunner in green chemistry, owing to its benign reaction conditions, high selectivity, tunable operating parameters, and eco-friendly features. Especially, the strategic synthesis of oxygen- and/or nitrogen-heterocyclic compounds holds great importance in across pharmaceutical, agrochemical, fragrance, polymeric, and clean energy sectors. Nevertheless, the electrochemical routes for crafting intricate heterocyclic compounds remain largely underexplored. Herein, we present an electrochemical [3 + 2] ring expansion approach that efficiently produces diverse O- and/or N-containing heterocyclic derivatives (e.g., 1,3-dioxolane, oxazoline, and cyclic carbonate) by fusing cheap and readily accessible precursors, e.g., acetone (CH₃COCH₃), acetonitrile (CH₃CN), or carbon dioxide (CO₂) with epoxide skeletons under ambient conditions. Experimental and computational investigations reveal the pivotal roles of cathodic noble metal nanocatalysts (e.g., Pt and Rh) deposited on carbon fibers and Lewis-acidic fluoroborate supporting electrolytes, promoting a kinetically favored concerted pathway over stepwise pathways in the electrocatalytic ring expansion cascade. Our analysis demonstrates that the differing activation energy barriers governing the crucial Lewis adduct [2π + 2σ]-cycloaddition step correlate with the higher reaction rate of acetone over acetonitrile, attributable to stronger electrostatic interactions observed in the acetone-participated reaction as elucidated by electrostatic potential surface analyses of transition states. This work underscores the prowess of electrochemical skeletal editing strategy in facilitating the green production of diversified heterocyclic organic compounds.