Asymmetric hydrogenation reductions, carbon-nitrogen

In this chapter and in Chapters 10-12, we will review and validate some methods for asymmetric (transfer) hydrogenation of carbon-oxygen and carbon-carbon double bonds catalysed by non-metallic systems, homogeneous transition metal catalysts and biocatalysts. Reduction of carbon-nitrogen double bond systems will be reported in another volume of this series. 

In addition to transfer hydrogenation reactions, arene ruthenium complexes also display excellent activity in the catalytic hydrogenation of olefins and alkynes including asymmetric reduction [40]. Remarkably, this process occurs under milder conditions, than required for catalysis with the dissociation of arene-metal bond. Lately, arene iridium complexes have also been found to be effective hydrogenation catalysts [41 ]. It is noteworthy that iridium can also promotes addition to the carbon-nitrogen double bond. 

An efficient asymmetric synthesis of a-amino acids has been described, having as its key step the stereoselective reduction of a carbon-nitrogen double bond in which the hydrogen atom addition is highly preferred from one diastereotopic face over the other. The sequence is shown for the synthesis of o-alanine. The optical purity observed is 96% in this instance, with optical yields of 92-97% reported for other amino acids prepared by this method. 

Most asymmetric reductions of carbon-nitrogen bonds involve catalytic hydrogenation. One example of a homogeneous asymmetric hydride transfer to an azomethine bond, however, is the... 

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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