Ruthenium-catalyzed dynamic kinetic

Box 9.1 Utility of the ruthenium-catalyzed dynamic kinetic resolution... 

Kim, M. J., Choi, Y. K., Choi, M. Y., Kim, M. and Park, J. (2001). Lipase/ruthenium-catalyzed dynamic kinetic resolution of hydroxy acids, diols, and hydroxy aldehydes protected with a bulky group.. Org. Chem., 66,4736-4738. 

Leijondahl, K., Boren, L., Braun, R., and Backvall, J.-E. (2009). Enzyme- and ruthenium-catalyzed dynamic kinetic asymmetric transformation of 1,5-diols. Application to the synthesis of (+)-Solenopsin A. /. Org. Chem., 74,1988-1993. 

Martin-Matute, B., Edin, M., and Backvall, J.-E. (2006). Highly efficient synthesis of enan-tiopure diacetylated C-2-symmetric diols by ruthenium- and enzyme-catalyzed dynamic kinetic asymmetric transformation (DYKAT). Chem. Eur.., 12,6053-6061. 

Scheme 5.11 Dynamic kinetic resolution of alcohol 18 by combination of enzymatic transesterification and ruthenium-catalyzed racemization.

Dynamic kinetic resolution is an excellent methodology to prepare enantiomeri-cally pure compounds and, in this context, chiral 4-(dimethylammo)pyridine (DMAP) iron and ruthenium " complexes have been reported to catalyze the... 

Dijksman, A. Elzinga, M., J. Li, Yu-Xin, Arends, I., Sheldon, R., A. Efficient ruthenium-catalyzed racemization of secondary alcohols application to dynamic kinetic resolution. Tetrahedron Asymmetry 2002, 13, 879-884. 

V Ratovelomanana-Vidal, J.-P. Genet, Synthetic Applications of the Ruthenium-Catalyzed Hydrogenation via Dynamic Kinetic Resolution, Can. J. Chem. 2000, 78, 846-851. 

It is worth mentioning the emergence of sequential catalytic processes involving a ruthenium-catalyzed step followed by a catalytic enzymatic transformation. This strategy has been developed by the groups of J.E. Backvall, and M.-J. Kim and J. Park especially for the dynamic kinetic resolution of alcohols (Scheme 50) [107-109]. 

Ratovelomanana-Vidal, V., Genet, J.-P. Synthetic applications of the ruthenium-catalyzed hydrogenation via dynamic kinetic resolution. 

Kitamura, M., Tokunaga, M., Noyori, R. Quantitative expression of dynamic kinetic resolution of chirally labile enantiomers stereoselective hydrogenation of 2-substituted 3-oxo carboxylic esters catalyzed by BINAP-ruthenium(ll) complexes. J. Am. Chem. Soc. 1993,115, 144-152. 

Scheme 19.5 Dynamic kinetic resolution of a secondary alcohol based on ruthenium-catalyzed racemization and enzymatic acylation.

The enzyme-catalyzed kinetic asymmetric transformation (KAT) of a diastereomeric 1 1 syn anti mixture is limited to a maximum theoretical yield of 25% of one enantiomer. This important drawback has been overcome by the combination of the actions of a ruthenium complex and a lipase in a dynamic kinetic asymmetric transformation (DYKAT), the desymmetrization of racemic or diastereomeric mixtures involving interconverting diastereomeric intermediates, implying different equilibration rates of the stereoisomers. Thus, this strategy allows the preparation of optically active diols, widely employed in organic and medicinal chemistry, as they are an important source of chiral auxiliaries and ligands and they can be easily employed as precursors of much other functionality. 

Bai W-J, Xie J-H, Li Y-L, Liu S, Zhou Q-L. Enantioselective synthesis of chiral (3-aryloxy alcohols by ruthenium-catalyzed ketone hydrogenation via dynamic kinetic resolution (DKR). Adv. Synth. Catal 2010 352(l) 81-84. 

Dynamic Kinetic Resolution (DKR) under Hydrogenation Conditions Ruthenium-catalyzed asymmetric hydrogenation of racemic a-substituted ketones via-dynamic kinetic resolution (DKR) is one of the elegant and powerful methods for the synthesis of chiral alcohols that simultaneously control two adjacent stereogenic centers with high levels of selectivity in a single chemical operation. This method was first reported... 

Genet JP, Pinel C, Mallart S, Juge S, Thorimbert S, Laffitte JA. Asymmetric synthesis. Practical production of D and L threonine. Dynamic kinetic resolution in rhodium and ruthenium catalyzed hydrogenation of 2-acylamino-3-oxobuty-rates. Tetrahedron Asymm. 1991 2(7) 555-567. 

Oxidation of aliphatic aldehydes by benzyltrimethylammonium chlorobromate to the corresponding carboxylic acid proceeds via the transfer of a hydride ion from the aldehyde hydrate to the oxidant. The oxidation of aUyl alcohol with potassium bromate in the presence of osmium(Vin) catalyst in aqueous acidic medium is first order in bromate, Os(Vni) and substrate, but inverse fractional order in H+ the stoichiometry of the reaction is 2 3 (oxidantsubstrate). The active species of oxidant and catalyst in the reaction were understood to be BrOs and H2OSO5, respectively, which form a complex. Autocatalysis by Br, one of the products, was observed, and attributed to complex formation between Br and osmium(VIII). First-order kinetics each in BrOs, Ru(VI), and substrate were observed for the ruthenium(VI)-catalyzed oxidation of cyclopentanol by alkaline KBrOs containing Hg(OAc)2. A zero-order dependence on HO concentration was observed and a suitable mechanism was postulated. The oxidation reaction of aniUne blue (AB+) with bromate at low pH exhibits interesting non-linear phenomena. The depletion of AB+ in the presence of excess of bromate and acid occurs at a distinctly slow rate, followed by a very rapid reaction. A 12-step reaction mechanism, consistent with the reaction dynamics, has been proposed. The novel cyclohexane-l,4-dione-bromate-acid system has been shown to exhibit a rapid oscillatory redox reaction superimposed on a slower... 

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