Electrochemical N-Propargylation of N-Heterocycles via Decarboxylation of Allenoic Acids

Broadly applicable and selective C–N bond formation remains a cornerstone challenge in organic synthesis. Although electrochemical methods have recently emerged as an efficient way for achieving decarboxylative C–N coupling, transforming allenoic acids into N-functionalized products remains elusive. Herein, we report the development of an electrochemical strategy for the decarboxylative N-propargylation of N-heterocycles using readily available 2,3-allenoic acids. By correlating the oxidation potentials of allenoic acids and nucleophilic coupling partners, we derived predictive criteria for anticipating reaction efficiency across a broad substrate scope. Mechanistic studies (cyclic voltammetry, in situ infrared (IR) kinetics, and density functional theory (DFT) calculations) support a two-step sequence involving oxidative decarboxylation to an allenyl radical rapidly oxidized to a highly electrophilic allenyl/propargyl cation and regioselective heterocycle attack yielding N-propargylated products. This work showcases a straightforward method for accessing reactive allenyl cation intermediates and expands the toolkit for sustainable electrosynthetic C–N bond formation.