Oppenauer-type oxidation of secondary alcohols catalyzed by homogeneous water-soluble complexes

Abstract

The catalytic system composed of [Ir(COD)Cl] 2 , 2,2′-biquinoline-4,4′-dicarboxylic acid dipotassium salt (BQC), and sodium carbonate is highly efficient for the selective oxidation of benzylic, 1-heteroaromatic, aliphatic, and allylic secondary alcohols using catalyst:substrate ratios ranging from 0.4% to 2.5%. Sterically hindered allylic alcohols undergo selectively good conversions to the corresponding enones, while unhindered ones are completely isomerized to saturated ketones. Mercury tests indicate that the catalytic process is likely homogeneous. The mechanism proposed for this Oppenauer-type oxidation including the isomerization process is based on iridium-alkoxide species.Key words: Oppenauer oxidation, water, catalysis, isomerization, secondary alcohols.