Catalytic dehydrogenation of 1,2- and 1,3-diols

• Dehydrogenation of 1,2-diols leads overwhelmingly to α-hydroxyketone (α-HK) as product.
• Tandem decarbonylation with Rh catalyst indicates α-hydroxyaldehydes (α-HAs) are likely intermediates
• α-HA transformation to more stable α-HK is by hydrogenation/rehydrogenation steps.

Described are studies of the dehydrogenation of 1,2- and 1,3-diols in homogenous solutions catalyzed by {[2,5-diphenyl-3,4-ditoluyl-(η5-C4CO)]2H}Ru2(CO)4(μ-H) (otherwise known as the Casey/Shvo catalyst). Both in the presence and absence of a dihydrogen acceptor, these reactions led to the analogous α-hydroxyketone as the only organic product. Isotopic labeling studies indicate that this product arises from reversible dehydrogenation/hydrogenation reactions, resulting in formation of the thermodynamically favored α-hydroxyketone. When this catalytic dehydrogenation was carried out in the presence of the rhodium decarbonylation catalyst Rh(dppp)2Cl (dppp = 1,3-bis(diphenylphosphino)propane), modest amounts of carbon monoxide result, suggesting that the dehydrogenation does generate at least some aldehydes that are intercepted by this catalyst. However, the efficiency of the latter reaction is poor.

Figure optionsDownload high-quality image (68 K)Download as PowerPoint slide