Aromatic coupling

The replacement of an electrofugic atom or group at a nucleophilic carbon atom by a diazonium ion is called an azo coupling reaction. By far the most important type of such reactions is that with aromatic coupling components, which was discovered by Griess in 1861 (see Sec. 1.1). It is a typical electrophilic aromatic substitution, called an arylazo-de-hydrogenation in the systematic IUPAC nomenclature (IUPAC 1989c, see Sec. 1.2). 

Most diazotized heteroaromatic amines undergo normal coupling reactions with common aromatic coupling components, as well as with CH acidic compounds (review Butler, 1975). 

Figure 5.20 Aromatic coupling with trifluoromethanesulfonate as leaving group.

Aromatic block copolymers, 282-284 Aromatic copolyesters, 18 Aromatic coupling, catalysts for, 289 Aromatic diamines, 180... 

Other reactions have been studied for synthesizing these polymers, including the electrophilic aromatic substitution of acyl and sulfonyl halides on aromatic reactants and the nickel-catalyzed aromatic coupling of aromatic dihalides [Yonezawa et al., 2000]. 

Several studies have been reported about Pd(II)-cataIyzed acetoxylation. Pd(OAc)2, which catalyzes aromatic coupling and nuclear acyloxylation as well (see Section 9.4.1), is an efficient catalyst of benzylic acetoxylation in the presence of alkali acetates. Stoichiometric oxidation in the absence of oxygen857,858 and a catalytic method858 are known. A twofold rate increase was observed when a mixture of Pd(OAc)2, Sn(OAc)2, and charcoal was employed in acetoxylation.859 Xylenes are converted to the a,a -diacetyloxy compounds in high yields.860... 

The substitution pattern for ring B is rather more variable but the usual aromatic couplings are observed. The appearance of the signals from ring C protons varies both with the location of the aryl ring B and with the oxidation state of the flavonoid. 

Aromatic coupling components can have the trialkylammoniumalkyl linked via a carboxamide group [43], e.g., 13. 

Stern has suggested511 a mechanism involving the rearrangement of a o-arylpal-ladium(II) species (the presumed intermediate in aromatic coupling) to a o-benzyl-palladium(II) species. The latter undergoes subsequent reductive elimination,... 

By far the most important azo coupling reaction, i.e. the reaction of arenediazonium ions with aromatic coupling components, has been known for many decades and has been extensively reviewed Therefore, in this section we shall concentrate on reactions of aliphatic diazonium ions, diazoalkanes and diazocarbonyl compounds which have not been known previously as well as on coupling reactions which have gained in importance more recently, specifically those of heterocyclic diazonium ions. 

Most diazotized heterocyclic amines undergo normal coupling reactions with common aromatic coupling components, as well as with some C—H acidic compounds . This pertains for five-membered ring systems such as pyrrols 46 pyrazoles imidazoles 45 , l,2,4-(49) and 1,2,3-triazoles 50... 

A method originally developed for terpenoid type off-flavor compounds was used [35]. By this method a JH NMR spectrum could be measured reliably from ca. 5 pg of monoterpenoid compound collected directly in the NMR solvent by preparative GC. A thick-wall (5 mm o.d., 2 mm i.d.) sample tube instead of a standard NMR tube was selected for the measurements in order to decrease the solvent volume from 700 to 100 pi. CH2C12 was found to be a suitable medium, because its JH NMR signal is locked at 5.30 ppm from tetramethylsilane (TMS). TheTi NMR spectral interpretation was mainly based on the synthetic procedure used, symmetry considerations of possible products, and characteristic intra-aromatic couplings. More details on the NMR spectroscopy of PCDTs and PCTAs are reported elsewhere [29,30,32]. 

COUPLING OF C(ip )-ORGANOMETALUCS WITH ARYL O, S AND Se COMPOUNDS COUPLING OFC(jp )-ORGANOMETALLICS WITH POLYFUNCTIONAL AROMATICS COUPLING OFC(jp )-ORGANOMETALUCS WITH HETEROAROMATIC HALIDES AND SULFIDES Furans and Thiophenes... 

In the field of symmetrical aromatic coupling, this method is particularly interesting with halides and triflates [12-14]. 

Jean A, Cantat J, Brard D, Bouchu D, Canesi S (2007) Novel method of aromatic coupling between iV-aryl methanesulfonamide and thiophene derivatives. Org Lett 9 2553-2556... 

Hydrogen fluoride (HF) is often used as a catalyst for alkenes, since there is less tar (fewer decomposition and polymeric by-products) and the volatile catalyst is easily removed. Both ferric chloride (FeCl3) and BF3 are common catalysts for alkene-aromatic coupling. Typical alkyne catalysts are aluminum chloride, gallium trichloride (GaCl3), BF3, and sulfuric acid. Reaction of a mixture of xylenes with a trace amount of BF3 in liquid HF gave the thermodynamic mixture 18% ortho, 60% meta, and 22% para but treatment with excess BF3 gave virtually 100% m-xylene. 07b,117... 

There are few known cases of azo coupling with classical aromatic coupling components, e.g., diazomethane, ethyl diazoacetate, and diazoketones with benzene-1,3,5-triol (Severin, 1958) and dicyanodiazomethane with A,A-dimethylaniline (Ciganek, 1965 a). 

A standard way to make aromatic amines is by nitration and reduction (Chapter 21) so we can think of making this aminobenzene from the nitrobenzene below. Now we can disconnect the two C-N bonds with the idea of putting a halide (X) at the point of substitution in each aromatic coupling partner. 

Comparison of oxidative aromatic coupling and the Scholl reaction 13AG(E)9900. 

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