Chemoselective Oxidation of Polyols with Chiral Palladium Catalysts

Chiral palladium-based catalysts
derived from pyridinyl oxazoline
(pyOx) ligands catalyze the oxidation of alcohols, including 1,2-diols,
triols, and tetraols, with high regio- and chemoselectivity. Screening
of various chiral oxazoline-derived ligands for the oxidation of a
model diol, 1,2-propanediol (1,2-PD), revealed that the nature of
the ligand had a significant influence on the activity and chemoselectivity
for oxidation of vicinal diols. The PyOx ligands containing an α-methyl
substituent were the most active for the oxidation of 1,2-PD using
benzoquinone as the terminal oxidant. Oxidation of vicinal diols and
polyols occurs selectively at the secondary alcohol to afford α-hydroxy
ketones in isolated yields of 62–87%. Chemoselective oxidation
of meso-erythritol with the chiral [(S)-(α-Me­(tert-Bu)­PyOx)­Pd­(OAc)]2[OTf]2 afforded (S)-erthyrulose in 62% yield and
24% ee.