Oximes heterogeneous hydrogenation

Heterogeneous hydrogenation of the C=N bond is a very widely used synthetic process with application to small and large-scale reactions. Many of the catalysts described in other sections may also be employed, for example those based on supported rhodium, palladium etc, and Raney Nickel. This area has been reviewed extensively recently192. Hydrogenation of oximes and hydrazones results in formation of amines. Milder conditions can be used for oxime reduction if the ethylaminocarbonyl derivative is prepared in situ prior to reduction276. 

Heterogeneous catalytic hydrogenation of a carbon-nitrogen double bond over a metal catalyst in the presence of a chiral compound was first carried out by Nakamura. Acetophenone oxime was hydrogenated over platinum black with ethyl menthoxyacetate or tartaric acid to give a-methylbenzylamine with 15-18% ee. 

One of the exciting results to come out of heterogeneous catalysis research since the early 1980s is the discovery and development of catalysts that employ hydrogen peroxide to selectively oxidize organic compounds at low temperatures in the liquid phase. These catalysts are based on titanium, and the important discovery was a way to isolate titanium in framework locations of the inner cavities of zeolites (molecular sieves). Thus, mild oxidations may be run in water or water-soluble solvents. Practicing organic chemists now have a way to catalytically oxidize benzene to phenols alkanes to alcohols and ketones primary alcohols to aldehydes, acids, esters, and acetals secondary alcohols to ketones primary amines to oximes secondary amines to hydroxyl-amines and tertiary amines to amine oxides. 

Hydrogen reduction of organic nitrogen compounds occurs readily in the presence of homogeneous and heterogeneous catalysts, " , e.g., nitro, nitroso, oxime, nitrile, imine, hydrazone and azide compounds are reduced ... 

The carbon-nitrogen double bonds of oximes and hydrazones are hydrogenated to form the corresponding amines by heterogeneous catalytic hydrogenation. 

Enantioselective heterogeneous catalytic hydrogenation using a chiral catalyst was pioneered by Aka-bori and Izumi, who prepared a palladium catalyst supported on silk fibroin. The oxime acetates of diethyl a-ketoglutarate or of ethyl phenylpyruvate were hydrogenated to form glutamic acid (7-15% ee) and phenylalanine (30% Similarly, a palladium-poly-L-leucine catalyst was used for the asym-... 

Historically, it took many years to achieve the almost perfect stereocontrol of an enantioselechve hydrogenahon reaction using a heterogeneous catalyst, with a resultant 97-99% enanhomeric excess (ee) of the product One of the oldest such examples is that of tartaric acid-modified platinum black for the hydrogenahon of an oxime to give a chiral amine of <20% ee [2]. Nonetheless, many reviews in this field have provided a clear history of the enanhoselechve catalysis from silk-palladium-a palladium metal supported on a chiral silk fiber to hydrogenate a... 

As expected, in the heterogeneous catalytic hydrogenation of norcamphor (R = H)85 and camphor (R = CH, )86 87 oximes, the amines resulting from hydrogenation of the imine from the least hindered side are formed. 

There are many classes of substrate structures involved in heterogeneous enantioselective hydrogenation on modified metal catalysts. They consist of 2-oxocarboxylic acids and their esters, ketones, diketones, keto lactones, imsaturated acids, oximes, and amides. Enantioselectivities of heterogeneous chirally modified metal catalysts are determined in an important way by the matched interactions between die functional groups of the substrate and the modifier. 

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