Ruthenium-catalyzed hydrogenation unsaturated carboxylic acids

Ohta, T., Takaya, H., Kitamura, M., Nagai, K., Noyori, R. Asymmetric hydrogenation of unsaturated carboxylic acids catalyzed by BINAP-ruthenium(ll) complexes. J. Org. Chem. 1987, 52, 3174-3176. 

Yoshikawa, K., Murata, M., Yamamoto, N., Inoguchi, K., Achiwa, K. Asymmetric reactions catalyzed by chiral metal complexes. III. The origin of the enantioselection in the ruthenium(ll)-catalyzed asymmetric hydrogenation of a,P-unsaturated carboxylic acid. Chem. Pharm. Bull. 1992, 40, 1072-1074. 

One of the standard methods for preparing enantiomerically pure compounds is the enantioselective hydrogenation of olefins, a,/3-unsaturated amino acids (esters, amides), a,/3-unsaturated carboxylic acid esters, enol esters, enamides, /3- and y-keto esters etc. catalyzed by chiral cationic rhodium, ruthenium and iridium complexes ". In isotope chemistry, it has only been exploited for the synthesis of e.p. natural and nonnatural H-, C-, C-, and F-labeled a-amino acids and small peptides from TV-protected a-(acylamino)acrylates or cinnamates and unsaturated peptides, respectively (Figure 11.9). This methodology has seen only hmited use, perhaps because of perceived radiation safety issues with the use of hydrogenation procedures on radioactive substrates. Also, versatile alternatives are available, including enantioselective metal hydride/tritide reductions, chiral auxiliary-controlled and biochemical procedures (see this chapter. Sections 11.2.2 and 11.3 and Chapter 12). 

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