Study of the Endocyclic versus Exocyclic C–O Bond Cleavage Pathways of α- and β‑Methyl Furanosides

The
activation and ring-opening of methyl furanosides in the four
natural sugar scaffolds (ribo, lyxo, arabino, and xylo) efficiently
afforded acyclic thioacetals with high SN2-like selectivity
at the acetal center in the presence of Me2BBr and thiophenol.
The stereochemical outcome of these reactions provides important mechanistic
insights into the activation pathway of five-membered semicyclic acetals.
The thioacetal products should find applications in oligosaccharides
synthesis and allow further development of acyclic strategies for
the synthesis of novel nucleoside analogues.