Tracking the leaving group in the remote activation of O-2-[(propan-2-yl)sulfinyl]benzyl (OPSB) glycoside.

In our recently developed interrupted Pummerer reaction mediated glycosylation with O-2-[(propan-2-yl)sulfinyl]benzyl (OPSB) glycosides as glycosyl donors, the anomeric leaving group was recovered as a benzyl alcohol which didn't affect the glycosylation efficiency. To investigate the mechanism of the occurrence of this alcohol, an 18O isotopic labeling reaction was carried out to track the leaving group. It was found that the benzyl alcohol was generated during the aqueous work up process from an inactive cyclic oxo-sulfonium ion intermediate. It was also proved that H2O prefer to attack the sulfur atom position during the hydrolysis of the intermediate.