Distinctive C–N cleavage/C–C formation mechanism in Au-catalyzed reactions of N-(o-alkynylphenyl)imines and vinyldiazo ketones†

DFT calculations were performed to evaluate the mechanisms of the Au-catalyzed reaction of N-(o-alkynylphenyl)imines and vinyldiazo ketones. It was found that the C–N cleavage/C–C bonding mechanism proposed in the previous literature cannot rationalize the experimental findings due to high energy demand involved. Alternatively, after the Au–π-coordination, intramolecular N-nucleophilic cyclization, C-attack of vinyldiazo ketone and OTf⁻ assisted H-shift, the de-diazotization promoted O-nucleophilic cyclization route was proposed. For further conversion, we established a unique Au⋯N σ-induced C–N cleavage/C–C bonding mechanism, over the usually known Au–π-coordination promoted one, in which (i) the presence of the Au⋯N σ-coordination contributes to the adjacent C¹–N¹ rupture, and (ii) the resultant sp²-C site is flexible to the energy-efficient configuration retention during the critical nucleophilic attack, effectively circumventing the high-energy inversion of configuration in the conventional anti-attack with the sp³-C site.