Olefin hydrogenation asymmetric, classes

Two ruthenium complexes, binap 3.43-Ru(OCOR)2(R = Me,CF3) [892] and binap 3.43-RuX2 (X = Cl, Br, I) [893, 894], are quite useful. The acetate and trifluoroacetate complexes of 3.43 induce selective asymmetric hydrogenations of classes of prochiral olefins that are poorly selective with rhodium complexes. These classes include a,(3- or fcy-unsaturated acids and esters, ally alcohols, j3-acylaminoacrylates and enamide precursors of isoquinoline alkaloids [752, 853, 859, 881, 883, 895]. 

Three classes of catalysts have been studied for the asymmetric hydrogenation of imines. One class of catalyst is generated from late transition metal precursors and bisphosphines. These catalysts have typically been generated from rhodium and iridium precursors. A second class of catalyst is based on the chiral titanocene and zirconocene systems presented in the previous section on the asymmetric hydrogenation of unfunctionalized olefins. The third class of catalyst is used for the transfer hydrogenation of imines and consists of ruthenium or rhodium complexes containing diamine, amino tosylamide, or amino alcohol ligands. " ... 

In general, of the mixed phosphorus-thioether ligands that have been used in the asymmetric hydrogenation of prochiral olefins, the thioether-phosphinite ligands have provided some of the best results. As an example, a new class of thioether-phosphinite ligands developed by Evans et al. has recently proved to be very efficient for the rhodium-catalysed asymmetric hydrogenation of a... 

Supercritical carbon dioxide represents an inexpensive, environmentally benign alternative to conventional solvents for chemical synthesis. In this chapter, we delineate the range of reactions for which supercritical CO2 represents a potentially viable replacement solvent based on solubility considerations and describe the reactors and associated equipment used to explore catalytic and other synthetic reactions in this medium. Three examples of homogeneous catalytic reactions in supercritical CC are presented the copolymerization of CO2 with epoxides, ruthenium>mediated phase transfer oxidation of olefins in a supercritical COa/aqueous system, and the catalyic asymmetric hydrogenation of enamides. The first two classes of reactions proceed in supercritical CO2, but no improvement in reactivity over conventional solvents was observed. Hythogenation reactions, however, exhibit enantioselectivities superior to conventional solvents for several substrates. 

Proline-derived phosphines (254) produced efficient catalysts in situ with [Ir(cod)]2BArp for the asymmetric hydrogenation of olefins in CH2CI2. These ligands gave high enantioselectivities with several classes of alkenes, most notably a,p unsaturated carboxylic esters and ketones. ... 

In the early 1990 s, Burk at Dupont spearheaded the development of new classes of biphospholane ligands - BPE (130) and DuPHOS (131) - that have significantly expanded the field of enantioselective hydrogenations [96-98]. As illustrated below, both enol esters (132, Equation 37) [96] and enamides (134, Equation 38) [97] were subjected to asymmetric reduction in the presence of Burk s catalysts to give the products in superb optical purities. An additional important feature of these systems is that the reductions can be conducted with mixtures of ( )- and (Z)-olefins, affording the same product in a stereoconvergent manner [96-98]. 

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