Gold(I)-Mediated Reactivity of Allenes with Mesoionic Nucleophiles: A Computational Study

We explore the factors leading to regioselective nucleophilic additions in gold(I)-mediated reactions with allenes through DFT analysis of model systems. The reactivity and selectivity are determined by both steric and electronic effects. The feasibility of intermolecular nucleophilic attack by sydnones and münchnones was evaluated by comparison to several known nucleophiles, with the transition state barriers of the latter being particularly accessible. The resulting intermediates are more likely to undergo formal (3+3) cyclisations instead of the more usual (3+2) pathways. While initial decarboxylation is not readily accessed, a computational mechanistic exploration suggests that the ultimate products are likely to be substituted dihydropyridines. We propose that the use of mesoionic reagents in gold(I)-mediated processes is feasible, should regioselectively access different heterocycles, and may lead to the development of new methodology in gold(I)-mediated synthesis.