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 1 H‐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 ).