Activation of arenes

Recently, synthesis of aryl ketones by a combination of palladium-catalyzed C-H activation of arenes and intermolecular carbopalladation of nitriles has been reported (Equation (119)).474... 

Ir(CH3)(Py)(trop-0,0)2] (trop=0,0-K -0,0-tropolonato) is also active catalyst for the C—H activation of arenes [58]. Mechanistic investigations for the Ir-catalyzed reaction have been studied [59]. 

The preparations of several (arene)(thiocarbonyl)chromium(0) complexes bearing electron-donating and/or electron-withdrawing substituents on the ring are described here (A-E). This type of compound is useful in organometallic chemistry for problems related to stereochemistry around a chromium atom6 and in organic chemistry in the activation of arene substituents with respect to alkylation.7... 

In 1982, Curtis and co-workers reported that Vaska s complex promotes the formation of phenylsiloxanes from the reaction of hydridosiloxanes and benzene in a catalytic, albeit low-yield, process.93 Catalytic arylsilane formation has also been reported by Tanaka and co-workers. Under photo-lytic conditions, RhCl(CO)(PMe3)2 catalyzes the C-H bond activation of arenes in reactions with hydrosilanes or disilanes, leading to the formation of new silicon-carbon bonds.94 More recently, C-H bond activation of arenes resulting in arylsilane formation has been observed in the... 

The least reactive (354) is mutagenic and the most reactive (253) is not mutagenic. This indicates that the chemical reactivity (both SN1 and SN2 reactions) forming a covalent carbon-nitrogen bond is not the only factor that determines the biological activity of arene oxides, though a certain minimum reactivity may be required. 

H. S. Taylor,/. Am. Chem. Soc. 1936, 58, 1445-1449. According to our search, the first time the phrase activation of C-H bond was used dates to 1929. Incidentally, authors referred to activation of arene C-H bonds by the substituents. 

I have reviewed, in Chapter No. 12, the activation of arenes by the strongly electron-withdrawing 12-electron fragment CpFe+, isolobal to Cr(CO)3 and Mn(CO)3+, and its application to the synthesis of dendritic cores, dendrons, dendrimers, and metallodendrimers, including molecular batteries. 

For 7r-activation of arenes by 12-electron electron-withdrawing groups, see Chapters 11 and 12 of this book. 

Scheme 1. Principle and general steps of the CpFe+-induced activation of arenes by temporary complexation.

Scheme 3. Benzylation activation of arenes by the 12-electron CpFe+ and the 13-electron CpFe groups (see also Scheme 4).

The oxidative activation of arenes is a powerful and versatile synthetic tactic that enables dearomatization to give useful synthons. Central to this chemistry are hydroxylated arenes or arenols, the phenolic functions of which can be exploited to facilitate the dearomatizing process by two-electron oxidation. Suitably substituted arenols can hence be converted, with the help of oxygen- or carbon-based nucleophiles, into ortho-quinone monoketals and ortho-quinols. These 6-oxocyclohexa-2,4-dienones are ideally functionalized for the construction of many complex and polyoxygenated natural product architectures. Today, the inherent and multiple reactivity of arenol-derived ortho-quinone monoketals and ortho-quinols species is finding numerous and, in many cases, biomimetic applications in modern organic synthesis. 

While the potential for other metal-ligand activation of arenes in nncleophile snbstitntion for chloride has been demonstrated, the processes have not been fully developed nor applied. The two-stage process of addition/substitution for chloride and arene detachment is exemplified for the iron system in equation (108). 

Indirect observation of activation of arene C-H bonds in phosphine and phosphite complexes of Ru and Os was reported. ... 

Aoyama Y, Yoshida T, Sakurai K-i, Ogoshi H (1983) Activation of arene carbon-hydrogen bonds. Direct electrophilic aromatic metalation with a rhodium-porphyrin complex. J Chem Soc Chem Commun 478-479... 

Jones reported an overview of the use of tris(pyrazolyl)borate rhodium complexes for the activation of arene and alkane C-H bonds, in particular detailing the fundamental studies with [Rh(CNR)(R)H(Tp )j. Selected example is reported in Fig. 8.12.154 Jones and coworkers155 also carried out some experiments in order to verify the involvement of... 

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