Mechanisms and Origins of Chemoselectivities of Gold(I)‐Catalyzed Nitrogenations of Alkynes with Trimethylsilyl Azide: A Computational Study

Abstract

Recently, Jiao and co‐workers reported an unprecedented gold‐catalyzed nitrogenation of alkynes with trimethylsilyl azide through C–C and C≡C bond cleavages. In this reaction, the acidic additive controls the chemoselectivity for the formation of either carbamides or aminotetrazoles from an internal alkyne. In this study, density functional theory calculations were performed to clarify the mechanism and origin of this chemoselectivity. A systematic search shows that the acidities of CH3SO3H and CF3SO3H determine which of the two reaction pathways is followed and, thus, the chemoselectivity. CH3SO3H favors the hydroxylation step and eventually leads to carbamide production. In contrast, CF3SO3H, which is a stronger acid than CH3SO3H, favors trimethylsilyl removal and eventually generates aminotetrazoles. This acid‐dependent chemoselectivity also applies to terminal alkynes and is consistent with the corresponding experimental results. Both CH3SO3H and CF3SO3H form carbamides preferentially because the hydrogen atom in a terminal alkyne promotes nucleophilic hydration more effectively than the n‐butyl group in an internal alkyne.