Efficient and selective azidation of per-O-acetylated sugars using ultrasound activation: application to the one-pot synthesis of 1,2,3-triazole glycosides

An inexpensive, simple and highly efficient process was developed for the selective anomeric azidation of protected sugars using a cooperative effect of iron catalysis and ultrasound activation, in the presence of SO2(N3)2. The latter, as a soluble azide source, is generated in situ by reaction of sodium azide with sulfuryl chloride under sonication. The obtained azidoglycosides undergo clean 1,3-dipolar cycloaddition with terminal alkynes under ultrasound activation to afford 1,2,3-triazole glycosides in high yields. These results illustrate that ultrasounds can significantly enhance the efficiency of both azidation and cycloaddition steps and lead to good overall yields. The stereo- and regioselectivities of the azidation and the 1,3-dipolar cycloaddition reactions have also been examined.