The identity of the unknown intermediate was still not clear after the NMR experiments, and therefore the glycosylation with the 1-β and the (R)-acceptor in Figure was carried out again, this time with the aim of trapping the intermediate. Thus the reaction was stopped after two hours, as the IR data suggested that the concentration of the intermediate would be at its maximum at this point. An NMR spectrum of the crude reaction mixture was recorded after a basic aqueous workup. The spectrum and experimental details can be found in SI (3.1.6). Both α-TCA, α-product, β-product, and hemiacetal were observed in the crude reaction mixture, but not the unknown intermediate. However, an observed J 1,2 of 3.40 Hz for the experiments in Figure indicates that the intermediate is an α-glycoside. In addition, an HSQC spectrum recorded during the kinetic NMR experiments (SI Figure , as it would be in accordance with the NMR data, and similar O-glycosides have been observed in self-promoted N -glycosylations with amide acceptors, as stable intermediates (Figure ). The distribution of O-glycoside and N -glycoside was shown to be solvent independent and the O-glycoside would rearrange to the N -glycoside upon heating. Thus, it is expected that the α-O-glycoside rearranges to the N -glycoside. Furthermore, the O-glycoside in Figure and similar glycosides are reported to give rise to a peak around 1627 cm -1 in IR-spectra, which is similar to the peak observed from the unknown intermediate (1600 -1625 cm -1 ).