Selective formation of beta-O-aryl glycosides in the absence of the C(2)-ester neighboring group.
The development of a general and practical method for the stereoselective synthesis of beta-O-aryl glycosides that exploits the nature of a cationic palladium(II) catalyst, instead of a C(2)-ester directing group, to control the beta-selectivity is described. This beta-glycosylation reaction is highly diastereoselective and requires 2-3 mol % of Pd(CH(3)CN)(4)(BF(4))(2) to activate glycosyl trichloroacetimidate donors at room temperature. The current method has been applied to d-glucose, d-galactose, and d-xylose donors with a nondirecting group incorporated at the C(2)-position to provide the O-aryl glycosides with good to excellent beta-selectivity. In addition, its application is widespread to electron-donating, electron-withdrawing, and hindered phenols. The reaction is likely to proceed through a seven-membered ring intermediate, wherein the palladium catalyst coordinates to both C(1)-trichloroacetimidate nitrogen and C(2)-oxygen of the donor, blocking the alpha-face. As a result, the phenol nucleophile preferentially approaches to the top face of the activated donor, leading to formation of the beta-O-aryl glycoside.
McKay
Matthew J
MJ
Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, USA.
Naab
Benjamin D
BD
Mercer
Gregory J
GJ
Nguyen
Hien M
HM
D000081:Acetamides; D002384:Catalysis; D062845:Chloroacetates; D004952:Esters; D006027:Glycosides / Q000138:chemical synthesis* / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D010165:Palladium; D013237:Stereoisomerism; D014238:Trichloroacetic Acid / Q000737:chemistry
D000081:Acetamides; D062845:Chloroacetates; D004952:Esters; D006027:Glycosides; D010165:Palladium; D014238:Trichloroacetic Acid; C009528:trichloroacetamide