Pd-Catalyzed Umpolung Chemistry of Glycal Acetates and Their [2,3]-Dehydrosugar Isomers

Glycals
and their [2,3]-dehydrosugar derivatives have commonly
been used in synthetic chemistry as electrophiles. Here we report
a Pd-catalyzed polar inversion (umpolung) of this reaction, where
the glycals and isomers can be used as nucleophiles. The reaction
showed high regio- and stereoselectivity in the presence of numerous
aromatic and aliphatic aldehydes. The synthetic utility of this reaction
was demonstrated by the short synthesis of the tetrahydropyran fragment
of the anticancer natural product mucocin.