Mechanisms of Cu/DMAP-cocatalyzed and DMAP-catalyzed C–N decarboxylative cross-coupling reactions†

A general and practical type of Cu/DMAP-cocatalyzed and DMAP-catalyzed C–N decarboxylative cross-coupling (DCC) reaction of carboxylic acids (or carboxylates) and azidoformates, which can construct both C(sp²)–N and C(sp³)–N bonds, was thoroughly investigated by density functional theory calculations. The Curtius rearrangements, i.e., extrusions of N₂, were found to be the rate-limiting steps for both Cu/DMAP-cocatalyzed and DMAP-catalyzed C–N DCC reactions. DMAP can facilitate the N₃⁻ transfer from the initial azidoformate species to the ensuing generated acyl azide intermediates. Then, the acyl azide intermediates undergo the Curtius rearrangements, overcoming a relatively low energy barrier. If DMAP was absent, the Curtius rearrangements would have to occur on the initial azidoformate species with energy barriers over 40.0 kcal mol⁻¹, which is not feasible at room temperature. Cu catalysts can further slightly facilitate the C–N DCC reactions.