Radical Mechanism of Isocyanide-Alkyne Cycloaddition by Multicatalysis of Ag₂CO₃, Solvent, and Substrate

Abstract

A combined DFT and experimental study was performed to reveal the mechanism of isocyanide-alkyne cycloaddition. Our results indicate that the mechanism of this valuable reaction is an unexpected multicatalyzed radical process. Ag₂CO₃ is the pivotal catalyst, serving as base for the deprotonation of isocyanide and oxidant to initiate the initial isocyanide radical formation. After the cycloaddition between isocyanide radical and silver-acetylide, substrate (isocyanide) and solvent (dioxane) replace the role of Ag₂CO₃. They act as a radical shuttle to regenerate isocyanide radical for the next catalytic cycle, simultaneously completing the protonation. Furthermore, the bulk solvent effect significantly increases the reactivity by decreasing the activation barriers through the whole reaction, serving as solvent as well as catalyst