Synthesis of α- and β-Glycosyl Isothiocyanates via Oxazoline Intermediates

摘要

A practical synthesis of acylated glycosyl isothiocyanates from sugar oxazolines, by reaction with thiophosgene, is reported. In the absence of any additive, the reaction is governed by the reverse anomeric effect, leading to the equatorially oriented isothiocyanate. However, in the presence of copper-(Ⅱ) chloride, the reaction proceeds preferentially with retention of the configuration at the anomeric center, providing the axial anomer as the major product. Noteworthy, this strategy allows accessing per-O-acetylated glycopyra-nosyl isothiocyanates with 1,2-cis relative configuration (e.g., the α-anomer in the D-gluco and D-galacto series), a problem that was outside the scope of previous methodologies.