GLYCOSYLIDENE CARBENES .9. REGIOSELECTIVE GLYCOSIDATION OF DIOLS AND TRIOLS - INTRAMOLECULAR AND INTERMOLECULAR HYDROGEN-BONDS

Glycosidation of the myo-inositol derivatives 2 and 3 by the diazirine 1 yields 90% of a diastereoisomer pair of beta-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 H-1-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).