Gold(I)-Catalyzed Intramolecular Diels-Alder Reaction: Evolution of Trappable Intermediates via Asynchronous Transition States.

In recent years allenes have been shown to be capable of exhibiting several modes of cycloadditions in the presence of transition metal catalysts that are otherwise unattainable for ethylene and acetylene. Herein, we predict that the [1 + 2]-cycloaddition pathway is accessible in a Au(I)-catalyzed reaction of allene with cis-1,3-butadiene. The electrophilicity of the central carbon of allene can be harnessed using a Au(I)-catalyst and -COOMe mediated stereoelectronics. A potential energy modification approach is applied to stabilize the diradicaloid intermediates. Our simulations establish that the product selectivity of the [4 + 2]- and [2 + 2]-pathways are steered by dynamical effects. Furthermore, a bioinspired version of this reaction is shown to afford an alternative synthetic pathway for proline and azepine analogs indicating rich prospects for thermal allene-butadiene reactions in drug discovery.