On the Memory of Chirality in Gold(I)-Catalyzed Intramolecular Carboalkoxylation of Alkynes

A computational study of the mechanism of the intramolecular carboalkoxylation of alkynes reported by Toste et al. allows the characterization of the chirality transfer process that makes this reaction enantioselective. Memory of chirality is preserved up until the stereocenter-generating iso-Nazarov cyclization through the synergy between the helicity of a pentadienyl cation intermediate and the control in the conformation of the allyl group, both elements defined upon alkoxy migration. The high barriers to conformational scrambling relative to those corresponding to chemical steps ensure the robustness of the chirality transfer mechanism and result in an unusual importance of conformational changes in reactivity that seems to be common in gold-catalyzed transformations.