Glycosylidene Carbenes. Part 9. Regioselective glycosidation of diols and triols: Intra‐ and intermolecular hydrogen bonds

Glycosidation of the myo‐inositol derivatives 2 and 3 by the diazirine 1 yields 90% of a diastereoisomer pair of β‐D‐glycosides in a 1:1 ratio, i.e. 5/6 and 7/8, respectively (Scheme 1). The crystal structure of 3 shows a strong intramolecular H‐bond, which persists in solution, as indicated by FT‐IR and 1H‐NMR spectra. Yields and diastereoselectivity are lower for the glycosidation of 24 by 1 (Scheme 3). The resulting 1,2‐ and 1,4‐linked disaccharides 25–28 were isolated as their acetates 29–32. The previously determined crystal structure of 24 shows no intramolecular H‐bonds. The yield of the glycosidation of 24, but not of 3, depends upon the concentration, indicating that activation of 24 by intermolecular H‐bonds is required. Glycosidation of 2 and 3 with the trichloroacetimidate 14 gave mixtures of four (5,6,15, and 16), and six (7,8, and 17–20) disaccharides, respectively (Scheme 2).