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

Identifier:  imarina:9294237

Handle: https://hdl.handle.net/20.500.11797/imarina9294237

Authors:  Garcia-Roca A; Pérez-Soto R; Stoica G; Benet-Buchholz J; Maseras F; Kleij AW

Abstract:
Metal-catalyzed propargylic transformations represent a powerful tool in organic synthesis to achieve new carbon-carbon and carbon-heteroatom bonds. However, detailed knowledge about the mechanistic intricacies related to the asymmetric formation of propargylic products featuring challenging heteroatom-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.