Ruthenium-catalysed reactions arenes

Rao s group studied the hydroTylation of esters, ketones and anilides. The ruthenium-catalysed ort/zo-hydro ylation of benzoates was found to be generally useful for the preparation of multi-functionalised arenes, some of which are difficult to synthesise via conventional methods. The reaction showed a good functional group tolerance and provided the products in high yields (Scheme 16). 

The ruthenium-catalysed arylation, by aryl halides, of benzylic amines carrying a pyridine coordinating group is thought to involve a concerted metallation-deprotonation pathway to give intermediates such as (96), followed by oxidative addition of the aryl halide to ruthenium and then reductive elimination. The reaction can be successM with aryl chlorides, as well as bromides and iodides, but here there are mechanistic differences. The ability of ruthenium to activate remote ring positions to electrophilic substitution has been referred to earlier, see Ref. 97. The reaction of ruthenium-coordinated 2-pyridyl arenes (51) with secondary alkyl halides has been shown to result in the formation of metfl-alkylated products. ... 

Dyson, P. J., Ellis, D. J., Henderson, W., Laurenczy, G. (2003). A comjjarison of ruthenium-catalysed arene hydrogenation reactions in water and l-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids. Adv. Synth. Catal., 345,1-2, 0anuaiy 2003) 216-221, ISSN 1615-4150... 

Reactions of arenes carrying a coordinating substituent with alkenes may give alkylated derivatives when catalysed by ruthenium biscarboxylate complexes. Experiments with deuterium-labelled compounds indicate that carbon-hydrogen metallation is reversible, so that reductive elimination from intermediates such as (90) is rate determining. Carboxylate-assisted ruthenium catalysis also allows the reaction of 2-arylpyridines with methylenecyclopropane to give derivatives, (91), in which the cyclopropane ring is conserved. ... 

Abstract The selective catalytic activation/functionalization of sp C-H bonds is expected to improve synthesis methods by better step number and atom economy. This chapter describes the recent achievements of ruthenium(II) catalysed transformations of sp C-H bonds for cross-coupled C-C bond formation. First arylation and heteroarylation with aromatic halides of a variety of (hetero)arenes, that are directed at ortho position by heterocycle or imine groups, are presented. The role of carboxylate partners is shown for Ru(II) catalysts that are able to operate profitably in water and to selectively produce diarylated or monoarylated products. The alkylation of (hetero)arenes with primary and secondary alkylhalides, and by hydroarylation of alkene C=C bonds is presented. The recent access to functional alkenes via oxidative dehydrogenative functionalization of C-H bonds with alkenes first, and then with alkynes, is shown to be catalysed by a Ru(ll) species associated with a silver salt in the presence of an oxidant such as Cu(OAc)2. Finally the catalytic oxidative annulations with alkynes to rapidly form a variety of heterocycles are described by initial activation of C-H followed by that of N-H or O-H bonds and by formation of a second C-C bond on reaction with C=0, C=N, and sp C-H bonds. Most catalytic cycles leading from C-H to C-C bond are discussed. 

NHC-Ru(II) complexes have been recently shown by Pinjing Zhao to perform the catalysed [3+2]carbocyclizations of alkynes with aromatic N-H ketimines [(Eq. 105)] [197]. The ruthenium(II) catalyst is based on jt-allyl precursor [(cod) Ru(q -methallyl)2] with addition of an NHCarbene as ligand, which is necessary for the reaction to take place and to occur at room temperature. Thus this catalyst significantly decreased this [3+2] annulation temperature. It is noteworthy that the C-H bond at the more electron-deficient arene favoured this reaction in non-polar solvents. 

Since 2011, the ruthenium(ll) catalysed alkenylation of arenes, alkenes, heterocycles, ferrocenes has been established as a catalytic method to produce a large variety of functional alkenes. The reaction requires a Ru(ll) catalyst associated with an oxidant such as Cu(0Ac)2.H20. More importantly using usually [RuCl2(arene)]2 catalyst with a slight excess of silver salt in the presence of an oxidant Cu(OAc)2 under air the alkenylation of (hetero)arenes and alkenes can be directed by weakly coordinating groups such as ketone, aldehydes, amides, carbamates, and esters. 

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