Chemoselective acetonation and one-pot glycosylation/acetylation of free sugars under ultrasonic green energy source

We report a convenient and highly efficient protocol for the acetonation of free sugars, enabling <i>cis-O-</i>isopropylidene saccharide derivatives under ultrasonic irradiation at ambient temperature. Triflic acid (TfOH) in acetone is identified as a mild and effective reagent for the chemoselective <i>O</i>-isopropylidenation of polyhydroxy compounds comprising aldo/keto-hexoses or aldo-pentoses. The synthetic utility of this approach was demonstrated through the preparation of various <i>O</i>-isopropylidene-protected sugar derivatives, which serve as key chiral intermediates for assembling important carbohydrate scaffolds and glycoconjugates. The use of ultrasonic irradiation as an environmentally benign energy source highlights the potential for this method to make a significant contribution to synthetic organic chemistry.