Arenes halides from

The smooth replacement of a heteroatom (usually halide) from arene ligands requires reversible addition of the nucleophile, since the kinetic site of addition is usually at a position bearing a hydrogen substituent (Scheme 3, path it]). 

As discussed in more detail in Section 4.7, which reviews studies on the reaction mechanism, the major product that competes with the arylamine is the arene resulting from hy-drodehalogenation of the aryl halide. Hartwig showed that steric hindrance was crucial to minimize formation of this side product when monophosphines are used [135]. A second side product from reaction of a primary amine is diaryl alkyl tertiary amine, resulting from... 

The first general route to (i76-arene)ruthenium(II) complexes, employing Ru(arene)22+ cations, has been developed by E. O. Fischer and co-workers. The cations were prepared by displacement of halides from RuC13 with Lewis acids, under reducing conditions, in the presence of arenes (3-5). 

Irradiation of haloarenes in the presence of amines in polar solvents promotes electron transfer from the eunine to the excited arene this can be followed by loss of halide from the resulting arene radical anion. Ultimately dehalogenated arenes are obtained. Two new reports of this process have been published, one for 9,10-dlchloroanthracene and the other for hexabromobenzene. ... 

In eontrast, dialkylhalonium salts sueh as dimethylbromonium and dimethyliodonium fluoroantimonate, whieh we prepared from excess alkyl halides with antimony pentafluoride or fluoroantimonie acid and isolated as stable salts (the less-stable chloronium salts were obtained only in solution), are very effective alkylating agents for heteroatom eompounds (Nu = R2O, R2S, R3N, R3P, ete.) and for C-alkylation (arenes, alkenes). 

A rational classification of reactions based on mechanistic considerations is essential for the better understanding of such a broad research field as that of the organic chemistry of Pd. Therefore, as was done in my previous book, the organic reactions of Pd are classified into stoichiometric and catalytic reactions. It is essential to form a Pd—C cr-bond for a synthetic reaction. The Pd— C (T-bond is formed in two ways depending on the substrates. ir-Bond formation from "unoxidized forms [1] of alkenes and arenes (simple alkenes and arenes) leads to stoichiometric reactions, and that from oxidized forms of alkenes and arenes (typically halides) leads to catalytic reactions. We first consider how these two reactions differ. 

Carbocations usually generated from an alkyl halide and aluminum chloride attack the aromatic ring to yield alkylbenzenes The arene must be at least as reactive as a halobenzene Carbocation rearrangements can occur especially with primary alkyl hal ides... 

A subsidiary approach involves nuclear modification of the arylsilanes so obtained. The requisite organometallics can be prepared from aryl halides, or by deprotonation of a suitably activated (c.g. methoxy-substituted) arene. A more specialized route involves cycloaddition between alkynylsilanes and diynes. 

Aerobic degradation of chlorinated arene hydrocarbons, including the important group PCBs, and chlorobenzoates that are produced from them as metabolites, is generally initiated by dihy-droxylation of the rings to dihydrodiols followed by dehydrogenation to catechols. Halide may be lost simultaneously and for 2-halogenated benzoates, both halide and carboxyl. Salient aspects are summarized, and attention drawn to selected aspects of enzyme inhibition. 

Palladium chemistry of heterocycles has its idiosyncrasies stemming from their different structural properties from the corresponding carbocyclic aryl compounds. Even activated chloroheterocycles are sufficiently reactive to undergo Pd-catalyzed reactions. As a consequence of a and y activation of heteroaryl halides, Pd-catalyzed chemistry may take place regioselectively at the activated positions, a phenomenon rarely seen in carbocyclic aryl halides. In addition, another salient peculiarity in palladium chemistry of heterocycles is the so-called heteroaryl Heck reaction . For instance, while intermolecular palladium-catalyzed arylations of carbocyclic arenes are rare, palladium-catalyzed arylations of azoles and many other heterocycles readily take place. Therefore, the principal aim of this book is to highlight important palladium-mediated reactions of heterocycles with emphasis on the unique characteristics of individual heterocycles. 

Aryldiazonium salts, usually obtained from arylamines, undergo replacement of the diazonium group with a variety of nucleophiles to provide advantageous methods for producing aryl halides, cyanides, phenols and arenes by reductive removal of the diazo group. Coupling reaction of aryldiazonium salts with phenols or arylamines give rise to the formation of azo dyes. 

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