Aryl compounds dimerization

In the presence of a precious metal catalyst, aryl halides can undergo dehalo-dimerization to give biaryl products, with varying degrees of selectivity. The major byproduct of this reaction is usually the dehalogenated aryl compound. This type of chemistry is currently one of the very few viable means for the large scale preparation of biaryl compounds. 

Intermolecular Stereoselective Aryl Coupling 2.1.1. Internal Asymmetric Induction with Chiral Substrates 2.1.1.1. Dimerization of Chiral Aryl Compounds... 

Getty, A. D. Goldberg, K. I. Reaction of a Pd(II) complex chelated by a tridentate PNC ligand with water to produce a [(PN)Pd(w-OH)]22+ dimer a rare observation of a well-defined hydrolysis of a Pd(II)—aryl compound. Organometallics 2001, 20, 2545—2551. 

With milled wood lignins or arylglycerol-/ -aryl ether dimers, the contribution of such C6C2 compounds amounts to less than 10% of that of the major CftC-i compounds. 

The P-alkyl iminophosphoranes are considerably more reactive than the P-aryl compounds, but iminophosphoranes with alkoxy or chloro groups are also known to participate in the reaction. N-alkyl- or N-aryltrichloroiminophosphoranes are usually obtained as four membered ring dimers, which on thermolysis generate the monomers. For example, thermolysis of the dimeric N-methyltrichloroiminophosphorane 63 in o-dichlorobenzene in the presence of phenyl isocyanate affords N-methyl-N -phenylcarbodiimide 64 in 57 % yield. 

Cyclopentadienone is an elusive compound that has been sought for many years but with little success. Molecular orbital calculations predict that it should be highly reactive, and so it is it exists only as the dimer. The tetraphenyl derivative of this compound is to be synthesized in this experiment. This derivative is stable, and reacts readily with dienophiles. It is used not only for the synthesis of highly aromatic, highly arylated compounds, but also for examination of the mechanism of the Diels-Alder reaction itself. Tetraphenylcyclopentadienone has been carefully studied by means of molecular orbital methods in attempts to understand its unusual reactivity, color, and dipole moment. In Chapter 48 this highly reactive molecule is used to trap the fleeting benzyne to form tetraphenylnaphthalene. Indeed, this reaction constitutes evidence that benzyne does exist. 

One feature of anionic polymerization is that it is possible to have polymerization occurring at both ends of an initiating dimer formed by electron transfer from a metal aryl compound such as sodium naphthalenide. This electron transfer results, in the case of styrene monomer, in the formation of a dianion ... 

Remko, M., and I. Tvaroska. 1987. Molecular orbital investigation on hgnin model compounds. XXL Solvent effect on the stability of P-aryl ether and benzyl aryl ether dimeric units of lignin. Holrforschung 41(6) 371-377. 

Remko, M. 1985. MO investigations on lignin model compounds. XVIII. Effect of the intramolecular hydrogen bond on the conformational stability of the P-aryl ether dimeric structural unit of lignin. Cell. Chem. Technol. 19(l) 47-50. 

Miki K., Renganathan V., Gold M.H. (1986) Mechanism of (3-aryl ether dimeric lignin model compound oxidation by lignin peroxidase of Phanerochaete chrysosporium. Biochemistry 25, 4790-6. 

Simple a,/3-unsaturated aldehydes, ketones, and esters participate preferentially in inverse electron demand (LUMOdlcne controlled) Diels-Alder reactions with electron-rich, strained, or simple olefinic and acetylenic dienophiles.3 5 The thermal reaction conditions for promoting the [4 + 2] cycloadditions of simple 1-oxabutadienes (R = H > alkyl, aryl > OR), cf. Eq. (1), are relatively harsh (150-250°C), and the reactions are characterized by competitive a,/3-unsaturated carbonyl compound dimerization or polymerization. Usual experimental techniques employed to compensate for poor conversions include the addition of radical inhibitors to the reaction mixture and the use of excess 1-oxabutadiene for promoting the [4 + 2] cycloaddition. Recent efforts have demonstrated that Lewis acid catalysis and pressure-promoted reaction conditions28-30 may be used successfully to conduct the [4 + 2] cycloaddition under mild thermal conditions (25-100°C). 

With aluminum or zinc and aluminum chloride in acetonitrile, dimerization of the ketyl is followed by rearrangements to benzopinacolones.m The reaction proceeds via an epoxide, which becomes the major product in the presence of ethylaluminum dichloride. Aryl or vinyl substituted carbonyl compounds dimerize sonochemically in the presence of TMSCl and zinc in ethers. Pinacol disilyl ethers are obtained in yields higher than those of the silent reaction. 12,113... 

Reactions.—Several interesting new developments in the chemistry of l,2-dithiole-3-thiones have been reported. 5-Aryl derivatives are converted, by anodic oxidation in acetonitrile, into dimeric dications, for example (10), which can be isolated as the insoluble perchlorate. With keten in benzene solution, the 5-aryl compounds give unstable green products which are formulated as thiolactones (11) treatment of these with acid... 

The dimerization of organic cyanides by co-ordination to dicyclopentadienyl-titanium(iii) aryl compounds has been reported [equation (6) R=Ph, o-MeCeH4, w-MeC6H4, p-MeCeH4, PhCHg, CeFs, or Cl Ri = Ph, o-MeCgHi, P-CIC6H4, or Me].2 Formation of the air-stable products occurs via [R CN] co-ordination,... 

A distinction between these four possibilities can be made on the basis of the kinetic isotope effect. There is no isotope effect in the arylation of deuterated or tritiated benzenoid compounds with dibenzoyl peroxide, thereby ruling out mechanisms in which a C5— bond is broken in the rate-determining step of the substitution. Paths (ii) and (iii,b) are therefore eliminated. In path (i) the first reaction, Eq. (6), is almost certain to be rate-determining, for the union of tw o radicals, Eq. (7), is a process of very low activation energy, while the abstraction in which a C—H bond is broken would require activation. More significant evidence against this path is that dimers, Arz, should result from it, yet they are never isolated. For instance, no 4,4 -dinitrobiphenyl is formed during the phenylation of... 

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