Highly Facialselective Synthesis of Pyranose 1,3-Oxazines and Their Ring Opening with Nucleophiles: A Novel Entry to 2-C-Branched Glycosides

A TMSOTf-promoted cycloaddition of N-benzoyl-N,O-acetals with various glycals and 3-deoxy glycals affords pyranose 1,3-oxazines with high facial selectivity. In addition, a highly diastereoselective ring opening of the resulting pyranose 1,3-oxazines is reported. With diverse nucleophiles, these reactions take place upon heating at 80 °C. This novel ring-opening reaction affords structurally diversified 2-C-branched glycosides with three newly formed contiguous stereocenters.