ISSN:
0170-2041
Keywords:
Carbohydrates
;
Chloral acetals
;
Epimerization
;
Glycosyl fluorides
;
Glycosylation
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Regio- and stereoselective acetalizations of methyl α-D-lyxopyranoside (1), methyl β-L-arabinopyranoside (6), methyl α-D-galactopyranoside (11), and methyl β-D-galactopyranoside (13) with chloral, including an inversion of the configuration at C-3, were achieved with dicyclohexylcarbodiimide as a coagent. Additionally, the formed methyl 3,4-O-(2,2,2-trichloroethylidene)-α-D-arabinopyranoside 2, methyl 2,3-O-(2,2,2-trichloroethylidene)-β-L-lyxopyranoside 7, methyl 2,3-O-(2,2,2-trichloroethylidene)-α-D-gulopyranoside 12, and methyl 2,3-O-(2,2,2-trichloroethylidene)-β-D-gulopyranosides 14 and 15 contain an N-cyclohexylcarbamoyl group vicinal to the chloral acetal moiety; the compounds 12 and 15, moreover, a formyl group in 6-position. The formyl and carbamoyl functions may be cleaved stepwise with methanolic sodium methoxide. Deformylation of the 6-O-formyl derivative 15 affords the urethane 16 with simultaneous migration of the carbamoyl group from the 4- to the 6-position. The fluorination of 3 and 8 with anhydrous hydrogen fluoride/nitromethane/acetic anhydride, giving the glycosyl fluorides 4 and 9 without any cleavage of the cyclic chloral acetal functions, is described. BF3-catalyzed glycosylations of chloro-ethanol with the fluorides 4 and 9α/β yield the α-glycoside 5 and the anomeric mixture 10α/β, respectively, showing that neither a cyclic chloral acetal function in 3,4-O-nor in 2,3-O-position affects such reactions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.199419941210
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