Carbon-oxygen double bonds catalytic hydrogenation

Catalytic hydrogenation of carbon-oxygen double bonds to the corresponding alcohols proceeds readily in the presence of various metal catalysts, usually under ambient conditions. Two reviews were published1,315 in 1987 and 1991, respectively, since our monograph appeared in 19852. In the latter book this field is summarized in detail with reference to earlier monographs. The present review shortly summarizes the results published recently and discusses the basic conclusions arrived at on the hydrogenation of oxo compounds. 

When the catalytic hydrogenation reaction is run under relatively mild conditions (room temperature and a pressure of hydrogen gas of several atmospheres or less), the reaction is very selective. Carbon-carbon double bonds of alkenes and carbon-carbon triple bonds of alkynes react readily, whereas carbon-carbon double bonds of aromatic rings and carbon-oxygen double bonds are usually inert under these reaction conditions. Some examples are provided in the following equations. Note that the stereochemistry of the addition reaction makes no difference in the first two examples. In the last example the major product results from syn addition. 

Catalytic hydrogenation of a,jS-unsaturated aldehydes and ketones yields saturated alcohols, addition of hydrogen occurring both at carbon-carbon and at carbon-oxygen double bonds. It is for the purpose of ultimately preparing saturated alcohols that the aldol condensation is often carried out. For example, /i-butyl alcohol and 2-ethyl-1-hexanol are both prepared on an industrial scale in this way ... 

This chapter concentrates solely on one type of reaction addition across the carbon-oxygen double bond of a carbonyl group. Except for catalytic hydrogenation, all the carbonyl additions arc polar reactions that exactly follow pathways that would be expected by clecliustaiics. 

The sequence begins by the initial condensation of the amine with the carbonyl component (Section 17-9) to produce the corresponding imine (for NH3 and primary amines) or iminium ion (secondary amines). Similar to the carbon-oxygen double bond in aldehydes and ketones, the carbon-nitrogen double bond in these intermediates is then reduced by simultaneous catalytic hydrogenation or by added special hydride reagents. 

The carbon-carbon double bond can be reduced by diimide prepared in solution in a number of ways.34 183,184 Oxidation of hydrazine with oxygen (air) or H202 in the presence of a catalytic amount of Cu(II) ion was the first method to generate and use diimide in hydrogenation.183-185 Acid-catalyzed decomposition of alkali azido-dicarboxylates,185,186 as well as thermal or base-catalyzed decomposition of aromatic sulfonyl hydrazides,183,184 are also useful methods for preparing the diimide reducing agent. 

It was discovered by Roelen in 1938 and is the oldest and largest volume catalytic reaction of alkenes, with the conversion of propylene to butyraldehyde being the mosi important. About 5 million tons of aldehydes and aldehyde derivatives (mostly alcohols) are produced annually making the process the most important industrial synthesis using a metal carbonyl complex as a catalyst. The name hydroformylation arises from the fact that in a formal sense a hydrogen atom and. formyl group are added across a double bond. The net result of the process is extension of (he carbon chain by one and introduction of oxygen into the molecule. 

Upon confronting the asymmetric carbon-nitrogen hydrogenation problem, we noted that, like a-enamides, A-acylhydrazones 32 possess an amide-like carbonyl oxygen that is similarly situated three atoms from the double bond to be reduced, and which could allow for chelation of the substrate to the catalytic Rh center. 

Levi, A., G. Modena, and G. Scorrano Asymmetric Reduction of Carbon-Nitrogen. Carbon-Oxygen, and Carbon-Carbon Double Bonds by Homogenous Catalytic Hydrogenation. J. Chem. Soc. Chem. Comm. 1975, 6. 

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