Glycosyl Fluorides as Intermediates in BF3·OEt2‐Promoted Glycosylation with Trichloroacetimidates

Abstract

Glycosyl fluorides have been found to be important intermediates in glycosylations with trichloroacetimidate donors and BF3·OEt2 activation (0.2–1 equiv.). Low‐temperature NMR spectroscopy experiments revealed that the α‐trichloroacetimidate was transformed into the glycosyl fluoride with inversion of stereochemistry, whereas the β anomer was not. A concerted mechanism was suggested for the stereospecific formation of glycosyl fluorides, which is not accounted for in the classic mechanism.