Comprehensive Mechanistic Scenario for the Cu-Mediated Asymmetric Propargylic Sulfonylation Forging Tertiary Carbon Stereocenters

Metal-catalyzed propargylic transformations repre-sent a powerful tool in organic synthesis to achieve new carbon- carbon and carbon-heteroatom bonds. However, detailed know-ledge about the mechanistic intricacies related to the asymmetric formation of propargylic products featuring challenging hetero-atom-substituted tertiary stereocenters is scarce and therefore provides an inspiring challenge. Here, we present a meticulous mechanistic analysis of a propargylic sulfonylation reaction promoted by a chiral Cu catalyst through a combination of experimental techniques and computational studies. Surprisingly, the enantio-discriminating step is not the coupling between the nucleophile and the propargylic precursor but rather the following proto-demetalation step, a scenario further validated by computing enantio-induction levels under other previously reported experimental conditions. A full mechanistic scenario for this propargylic substitution reaction is provided, including a catalyst pre-activation stage, a productive catalytic cycle, and an unanticipated non-linear effect at the Cu(I) oxidation level.

Automated summary

Metal-catalyzed propargylic transformations are a powerful tool in organic synthesis for forming new carbon-carbon and carbon-heteroatom bonds. However, there is limited knowledge about the mechanistic intricacies of asymmetric propargylic reactions with challenging heteroatom substitution, presenting an inspiring challenge. This study presents a detailed mechanistic analysis of a propargylic sulfonylation reaction promoted by a chiral Cu catalyst through experimental techniques and computational studies. Surprisingly, the enantio-discriminating step was found to be the proto-demetalation step, rather than the coupling between the nucleophile and the propargylic precursor.