Ruthenium-catalyzed arylations

Ruthenium-catalyzed arylations of aromatic ketones were reported employing the transmetallation of boronic esters (Equations (127) and (128)).112... 

Very recently, Kakiuchi reported on the ruthenium-catalyzed arylation of C-H bonds using organoborane reagents. The reaction of aromatic ketones with arylboro-nates using a ruthenium catalyst resulted in the production of arylated aromatic ketones (Eq. 9.36) [50], This arylation reaction using arylboronates can be applied to a variety of aromatic ketones and arylboronates. The authors proposed that this reaction involves the oxidative addition of a C-H bond to a Ru(0) species. 

Scheme 14 Ruthenium-catalyzed arylation of ketone 36 in pinacolone...

Scheme 15 Proposed mechanism for ruthenium-catalyzed arylations of ketones with boronates...

Ackermann L (2005) Phosphine oxides as preligands in ruthenium-catalyzed arylations via C-H bond functionalization using aryl chlorides. Org Lett 7 3123-3125... 

Oi, S., Sakai, K. and Inoue, Y. (2005) Ruthenium-catalyzed arylation of 2-alkenylpyridines with aryl bromides alternative ,Z-selectivity to Mizoroki-Heck reaction. Org. Lett., 7, 4009-11. 

Phosphine Oxides as Preligands in Ruthenium-Catalyzed Arylations via C-H Bond Functionalization Using Aryl Chlorides... 

Ruthenium-catalyzed arylation seems to favor the proton abstraction mechanism. We studied the coupling of an aryl group to a phenylpyridine moiety [64]. The first step consists of cleavage of a C- H bond to form a Ru-C bond. The two mechanisms, oxidative addition on the ruthenium or H-abstraction, were evaluated. As for palladium, the oxidation of Ru(II) to Ru(IV) is energetically disfavored with a barrier of 133 kJ/mol. The H-abstraction possesses a much lower barrier, 35 kJ/mol with HCOs" as proton abstractor (Fig. 11.13). The barrier of H-abstraction is sensitive to the nature of the base it is only of 22 kJ/mol with acetate. 

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... 

The ruthenium-catalyzed isomerization of aryl allyl ethers or amines followed by ring-closing metathesis with ruthenium catalyst 1 furnishes fused benzo-heterocycles in good yield (Scheme 40).66 67... 

In addition to aryl halides and triflates, organometallic reagents can be utilized for the catalytic arylation reaction. The rhodium-catalyzed arylation of arylpyridines proceeds with the use of tetraarylstannanes (Equation (67)).83 The ruthenium-catalyzed reaction of aromatic ketones with arylboronates affords the ortho-arylated aromatic ketones (Equation (68)).84... 

Recently, the first report was made on the ruthenium-catalyzed enantioselective hydrogenation of aryl-methyl ketones using monodentate phosphonites (Scheme 28.18). In particular, ligand 15f induced excellent ee-values. One very early report on rhodium-catalyzed hydrogenation of ketones using the monophosphine bmpp 1 f met with a low e.e. [95]. 

Ursini, C.V., Dias, G.H.M. and Rodrigues, J.A.R., Ruthenium-catalyzed reduction of racemic tricarbonyl( 7 -aryl ketonejchromium complexes using transfer hydrogenation a simple alternative to the resolution of planar chiral organometallics. J. Organomet. Chem., 2005,690, 3176. 

This article presents the principles known so far for the synthesis of metal complexes containing stable carbenes, including the preparation of the relevant carbene precursors. The use of some of these compounds in transition-metal-catalyzed reactions is discussed mainly for ruthenium-catalyzed olefin metathesis and palladium-Znickel-catalyzed coupling reactions of aryl halides, but other reactions will be touched upon as well. Chapters about the properties of metal- carbene complexes, their applications in materials science and medicinal chemistry, and their role in bioinorganic chemistry round the survey off. The focus of this review is on ZV-heterocyclic carbenes, in the following abbreviated as NHC and NHCs, respectively. 

In (C5Me5)Rh(C2H3SiMe3)2-catalyzed C-H/olefin coupling the effect of the coordination of the ketone carbonyl is different from that in the ruthenium-catalyzed reaction [10], In the rhodium-catalyzed reaction all C-H bonds on the aromatic ring are cleaved by the rhodium complex without coordination of the ketone carbonyl. Thus, C-H bond cleavage and addition of Rh-H to olefins proceed without coordination of the ketone carbonyl. After addition of the Rh-H species to the olefin, a coordinatively unsaturated Rh(aryl) (alkyl) species should be formed. Coordination of the ketone carbonyl group to the vacant site on the rhodium atom leads... 

Eilbracht et al. have developed rhodium- or ruthenium-catalyzed one-pot synthesis of cyclopentanones from allyl vinyl ether via tandem Claisen rearrangement and hydroacylation [109-111]. This protocol requires elevated temperature (140-220°C) and also requires alkyl or aryl substituents at the terminal position of the allylic double bond to prevent undesirable double bond migration in the intermediary formed, unsaturated aldehyde. 

Ruthenium-Catalyzed Direct Arylations Through C-H Bond Cleavages... 

Abstract Stoichiometric cycloruthenation reactions of substrates containing Lewis-basic functionalities set the stage for efficient ruthenium-catalyzed C-H bond functionalization reactions. Thereby, selective addition reactions of C-H bonds across alkenes or alkynes enabled atom-economical synthesis of substituted arenes. More recently, ruthenium-catalyzed direct arylation reactions were examined, which display an unparalleled scope and, hence, represent economically and environmentally benign alternatives to traditional cross-coupling chemistry. 

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