Oppenauer oxidation, catalysis

Meerwein-Pondorf-Verley reduction, discovered in the 1920s, is the transfer hydrogenation of carbonyl compounds by alcohols, catalyzed by basic metal compounds (e.g., alkoxides) [56-58]. The same reaction viewed as oxidation of alcohols [59] is called Oppenauer oxidation. Suitable catalysts include homogeneous as well as heterogeneous systems, containing a wide variety of metals like Li, Mg, Ca, Al, Ti, 2r and lanthanides. The subject has been reviewed recently [22]. In this review we will concentrate on homogeneous catalysis by aluminium. Most aluminium alkoxides will catalyze MPV reduction. 

Keywords Rhodium Iridium Catalysis Oppenauer-type oxidations ... 

Creyghton, E. J., Van derWaai, J. 0. Meenwein-Ponndorf-Verley reduction, Oppenauer oxidation, and related reactions. Fine Chemicals through Heterogeneous Catalysis 2001,438-448. 

The same research group also investigated sulfonylamino alumino bisphenoxides, one of their best MPV catalytic systems and tuned these compounds towards pure Oppenauer oxidation catalysis (Scheme 18.17). The aluminium alkoxides, generated in situ, very efficiently catalyse the oxidation of the test substrate carveol in toluene with 1.2 equiv of pivalde-hyde as hydride acceptor to give carvone in 94% yield (1 mol% catalyst, RT, 1 h). A wide range of alcohols including secondary aliphatic and benzylic... 

When heated in the presence of a carboxyHc acid, cinnamyl alcohol is converted to the corresponding ester. Oxidation to cinnamaldehyde is readily accompHshed under Oppenauer conditions with furfural as a hydrogen acceptor in the presence of aluminum isopropoxide (44). Cinnamic acid is produced directly with strong oxidants such as chromic acid and nickel peroxide. The use of t-butyl hydroperoxide with vanadium pentoxide catalysis offers a selective method for epoxidation of the olefinic double bond of cinnamyl alcohol (45). 

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