Premium
Glycosylidene Carbenes. Part 16. Glycosidation of methyl 6‐ O ‐trityl‐α‐ D ‐altropyranoside
Author(s) -
Bozó Eva,
Vasella Andrea
Publication year - 1994
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19940770316
Subject(s) - chemistry , regioselectivity , intramolecular force , anomer , triol , protonation , stereoselectivity , medicinal chemistry , nuclear magnetic resonance spectroscopy , hydrogen bond , stereochemistry , ion , organic chemistry , molecule , catalysis , diol
Hydrogen bonding of the triol 4 in chlorinated solvents was studied by IR (CH 2 Cl 2 and CCl 4 ) and 1 H‐NMR spectroscopy (CDCl 3 ), and the regioselectivity of the glycosidation of the triol 4 by the diazirine 1 is predicted on the basis of two assumptions: preferred protonation of the intermediate glycosylidene carbene by the OH group involved in the weakest intramolecular H‐bond, and attack in the π‐plane of the thereby generated oxycarbenium cation either by the reoriented oxy anion, or by a properly oriented vicinal OH group. Glycosidation led to the disaccharides 5–10 ( Scheme ) which were separated and characterized as their acetates 11–16 , to the lactone azines 17 and to the 2‐(benzyloxy)glucal 18 . In agreement with the predictions, glycosidation in non‐coordinating solvents gave the 1,2‐, 1,3‐, and 1,4‐linked disaccharides in decreasing relative amounts. Glycosidation in THF proceeded with a lower degree of regioselectivity and led preferentially to the β ‐ D ‐anomers, except for the minor, 1,4‐linked disaccharides, where THF had only a weak influence on stereoselectivity at room temperature and led to a slight increase of the α ‐ D ‐anomer at −80°.