O-(α-D-Glucopyranosyl)trichloroacetimidate as a Glucosyl Donor

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Abstract
Model reactions of 0-(α-D-glucopyranosyl)trichloroacetimidate 2α with methanol and choTesterol under various conditions demon-strated that stereocontrolled glucosyl transfer with inversion of configuration at the anomeric center is best carried out in di-chloromethane at low temperatures with boron trifluoride-ether as a catalyst. Under these conditions β-glucoside 4β and β-disaccha-rides 5β- 9β were obtained in good to excellent yields. With Brtosnsted acids, fast glucosyl transfer to the acid anion was mainly observed and required no further acidic catalysis. With strong acids formation of the thermodynamically more stable product dominated. However, with the weaker carboxylic acids highly diastereoselective inversion of configuration at the anomeric center led, for instance, to β-1-O-acyl derivatives 11β - 18β, revealing a convenient method for the synthesis of O-glycosyl-carb-oxylates. This method was also applied to resolution of racemic carboxylic acids. Similar results were obtained with N-nucleophiles. Hydrazoic acid gave exclusively α-azide 19a. Nitrogen heterocycles gave with boron trifluoride-ether catalysis mainly β-nucleosides 20β - 23β. Reaction of trichloroacetimidate 2α with O-nucleophiles in aceto-nitrile as solvent led to different products due to competition