Journal
JOURNAL OF ORGANIC CHEMISTRY
Volume 74, Issue 4, Pages 1650-1657Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jo802468p
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Funding
- Montana State University
- National Science Foundation [CHEM-0809200]
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The development of a new glycosylation method for the stereoselective synthesis of beta-glycosides in the absence of the traditional C(2)-ester neighboring group effect is described. This process relies on the ability of the cationic palladium catalyst, Pd(PhCN)(2)(OTf)(2) generated in situ from Pd(PhCN)(2)Cl-2 and AgOTf, to direct beta-selectivity. The new glycosylation reaction is highly beta-selective and proceeds under mild conditions with 1-2 mol % of catalyst loading. This beta-glycosylation method has been applied to a number of glucose donors with benzyl, allyl, and p-methoxybenzyl groups incorporated at the C(2)position as well as tribenzylated xylose and quinovose donors to prepare various disaccharides and trisaccharides with good to excellent beta-selectivity. Mechanistic studies suggest that the major operative pathway is likely to proceed via a seven-membered ring intermediate, wherein the cationic palladium complex coordinates to both the C(1)-imidate nitrogen and C(2)-oxygen of the trichloroacetimidate donor. Formation of this seven-membered ring intermediate directs the selectivity, leading to the formation of beta-glycosides.
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