Olefin , catalytic asymmetric arylation

There is no doubt that catalytic asymmetric synthesis has a significant advantage over the traditional diastereomeric resolution technology. However, it is important to note that for the asymmetric hydrogenation technology to be commercially useful, a low-cost route to the precursor olefins is just as crucial. The electrocarboxylation of methyl aryl ketone and the dehydration of the substituted lactic acids in Figures 5 and 6 are highly efficient. Excellent yields of the desired products can be achieved in each reaction. These processes are currently under active development. However, since the subjects of electrochemistry and catalytic dehydration are beyond the scope of this article, these reactions will be published later in a separate paper. 

Asymmetric epoxidation of olefins with ruthenium catalysts based either on chiral porphyrins or on pyridine-2,6-bisoxazoline (pybox) ligands has been reported (Scheme 6.21). Berkessel et al. reported that catalysts 27 and 28 were efficient catalysts for the enantioselective epoxidation of aryl-substituted olefins (Table 6.10) [139]. Enantioselectivities of up to 83% were obtained in the epoxidation of 1,2-dihydronaphthalene with catalyst 28 and 2,6-DCPNO. Simple olefins such as oct-l-ene reacted poorly and gave epoxides with low enantioselectivity. The use of pybox ligands in ruthenium-catalyzed asymmetric epoxidations was first reported by Nishiyama et al., who used catalyst 30 in combination with iodosyl benzene, bisacetoxyiodo benzene [PhI(OAc)2], or TBHP for the oxidation of trons-stilbene [140], In their best result, with PhI(OAc)2 as oxidant, they obtained trons-stilbene oxide in 80% yield and with 63% ee. More recently, Beller and coworkers have reexamined this catalytic system, finding that asymmetric epoxidations could be perfonned with ruthenium catalysts 29 and 30 and 30% aqueous hydrogen peroxide (Table 6.11) [141]. Development of the pybox ligand provided ruthenium complex 31, which turned out to be the most efficient catalyst for asymmetric... 

Jacobsen reported in 1990 that Mnm complexes of chiral salen ligands (41) were the most efficient catalysts available for the enantioselective epoxidation of alkyl- and aryl-substituted olefins.118 This stimulated a rapid development in the chemistry and applications of chiral SB complexes, which offer promising catalytic applications to several organic reactions, such as enantioselective cyclopropanation of styrenes, asymmetric aziridination of olefins, asymmetric Diels-Alder cycloaddition, and enantioselective ring opening of epoxides.4,119... 

Optically active alcohols, amines, and alkanes can be prepared by the metal catalyzed asymmetric hydrosilylation of ketones, imines, and olefins [77,94,95]. Several catalytic systems have been successfully demonstrated, such as the asymmetric silylation of aryl ketones with rhodium and Pybox ligands however, there are no industrial processes that use asymmetric hydrosilylation. The asymmetric hydrosilyation of olefins to alkylsilanes (and the corresponding alcohol) can be accomplished with palladium catalysts that contain chiral monophosphines with high enantioselectivities (up to 96% ee) and reasonably good turnovers (S/C = 1000) [96]. Unfortunately, high enantioselectivities are only limited to the asymmetric hydrosilylation of styrene derivatives [97]. Hydrosilylation of simple terminal olefins with palladium catalysts that contain the monophosphine, MeO-MOP (67), can be obtained with enantioselectivities in the range of 94-97% ee and regioselectivities of the branched to normal of the products of 66/43 to 94/ 6 (Scheme 26) [98.99]. 

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