Selective formation of beta-O-aryl glycosides in the absence of the C(2)-ester neighboring group

J Org Chem. 2009 Jul 3;74(13):4705-11. doi: 10.1021/jo9002807.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Acetamides
  • Catalysis
  • Chloroacetates*
  • Esters
  • Glycosides / chemical synthesis*
  • Glycosides / chemistry*
  • Magnetic Resonance Spectroscopy
  • Palladium
  • Stereoisomerism
  • Trichloroacetic Acid / chemistry

Substances

  • Acetamides
  • Chloroacetates
  • Esters
  • Glycosides
  • Palladium
  • Trichloroacetic Acid
  • trichloroacetamide