The 4K reaction

The classical Koenigs-Knorr glycosidation of bromides or chlorides promoted with Ag 2 O or Ag 2 CO 3 works only with reactive substrates (ideally both donor and acceptor). This reaction was found to be practically ineffective with unreactive donors such as per- O -benzoylated mannosyl bromide. Recently, it was discovered that the addition of catalytic (Lewis) acids to a silver salt-promoted reaction has a dramatic effect on the reaction rate and yield. A tentative mechanism for this cooperatively-catalyzed glycosylation reaction has been proposed, and the improved understanding of the reaction led to more efficient protocols and broader applications to a variety of glycosidic linkages. Since Ag 2 O-mediated activation was introduced by German chemists K oenigs and K norr, and “cooperatively catalyzed” is Kooperativ Katalysiert in German, we refer to this new reaction as “the 4K reaction.”