Tandem one-pot acetalation-acetylation for direct access to differentially protected thioglycosides and O-glycosides with p-toluenesulfonic acid

A new tandem one-pot acetalation-acetylation procedure is reported which streamlines routine protecting-group manipulation of carbohydrate molecules in production of differentially protected O- and thioglycosides. This new procedure eliminates the use of highly toxic pyridine, and p-toluenesulfonic acid is employed as catalyst for acetalation and acetylation. Synthetic utility of the new procedure is demonstrated in the expeditious preparation of differentially protected glycosides from a wide variety of carbohydrate substrates including unprotected O-glycosides, thioglycosides, and N-acetyl neuraminic acid ester.