74808-06-3Relevant articles and documents
Glycosyl Imidates, 12. - Direct Synthesis of O-α- and O-β-Glycosyl Imidates
Schmidt, Richard R.,Michel, Josef,Roos, Michael
, p. 1343 - 1357 (2007/10/02)
1-O-Unsubstituted aldoses afford with halogen-activated nitriles under base catalysis directly O-α- and O-β-glycosyl imidates which can be isolated as stable compounds.Investigations with 2,3,4,6-tetra-O-benzyl- and -acetylglucose (1a, b), trichloroacetonitrile and trifluoroacetonitrile and NaH and K2CO3, respectively, as base have demonstrated, that the β-glucopyranosyl-1-oxido oxygen atom is more nucleophilic (rapid formation of 3a-β, 3b-β, 4a-β, and 4b-β) than the α-glycopyranosyl-1-oxido oxygen atom.Because of the reversibility of these reactions, however,due to the anomeric effect finally the thermodynamically more stable α-imidates 3a-α, 3b-α, 4a-α, and 4b-α are formed exclusively.Therefore O-α- and O-β-glycosyl imidate formation can be conducted highly diastereoselectively. - From trichloroacetonitrile and other 1-O-unsubstituted carbohydrates the imidates 7-α - 13-β were obtained as stable compounds. - Less activated nitriles (chloroacetonitrile, dichloroacetonitrile) have proven not or not so successful in the direct O-glycosyl imidate formation. - N-Aryl ketenimines yielded cleanly base-catalyzed direct O-glycosyl imidate formation.However, because of the irreversibility of this reaction under the reaction conditions only kinetic product formation was observed (leading to the β-imidates 14a-β - 14d-β and 15d-β.Similarly 1-O-unprotected mannose gave only the β-product 16d-β.
