Synthesis, characterization and X-ray structure of glycosyl-1,2-isoxazoles and glycosyl-1,2-isoxazolines prepared via 1,3-dipolar cycloaddition

A convenient preparative method of a series of glycosyl-1,2-isoxazoles (6–11) and glycosyl-1,2-isoxazolines (15–20) by a simple and efficient 1,3-dipolar cycloaddition of a series of aryl nitrile oxide, generated in situ from aryl oximes (4–5), with a variety of O-propargyl glycosyles (1–3) or O-allyl glycosyles (12–14) respectively, is reported. The carbohydrate-containing 1,2-isoxazoles and 1,2-isoxazolines compounds were isolated in excellent yields (81–91%) and they were fully characterized by 1H, 13C NMR and mass spectrometry. The relative stereochemistry of the glycosyl-1,2-isoxazole 10 was confirmed by single crystal X-ray analysis. The molecular structure of 10 confirms the retention of both, the anomeric stereochemistry of the D-fructose as well as the placement of the acetal groups.