Unraveling the Mechanism of Stereospecific Self-promoted N-Glycosylations

In this study, the mechanism of self-promoted N-glycosylations is extensively investigated through kinetic experiments, computational studies, and nucleophilic competition experiments. Based on the findings, the mechanism is proposed to be initiated by proton transfer from the acidic sulfonyl carbamate to the trichloroacetimidate, upon formation of an associated contact ion pair. This ion pair then collapses in an S_N1-like fashion, with formation of an oxocarbeniumion-like intermediate. According to the proposed mechanism, stereospecificity arises from the associated nature of all intermediates formed throughout the reaction. During the mechanistic study, it was also found that the sulfonyl carbamates have catalytic properties if a competing nucleophile is present.