Glycosidation of Thioglycosides in the Presence of Bromine: Mechanism, Reactivity, and Stereoselectivity

Elaborating on previous studies by Lemieux for highly reactive “armed” bromides, we discovered that β-bromide of the superdisarmed (2-<i>O</i>-benzyl-3,4,6-tri-<i>O</i>-benzoyl) series can be directly obtained from the thioglycoside precursor. When this bromide is glycosidated, α-glycosides form exclusively; however, the yields of such transformations may be low due to the competing anomerization into α-bromide that is totally unreactive under the established reaction conditions