Addition benzene derivatives

Benzoic acid and naphthoic acid are formed by the oxidative carbonylation by use of Pd(OAc)2 in AcOH. t-Bu02H and allyl chloride are used as reoxidants. Addition of phenanthroline gives a favorable effect[360], Furan and thiophene are also carbonylated selectively at the 2-position[361,362]. fndole-3-carboxylic acid is prepared by the carboxylation of 1-acetylindole using Pd(OAc)2 and peroxodisulfate (Na2S208)[362aj. Benzoic acid derivatives are obtained by the reaction of benzene derivatives with sodium palladium mal-onate in refluxing AcOH[363]. 

A -Amino- and A-substituted amino-pyrroles readily undergo Diels-Alder additions and add to activated alkynes at room temperature. The resulting azanorbornadienes extrude A-aminonitrenes and this forms the basis of an unusual synthesis of benzene derivatives (81S753,81TL3347). It has been found that ethyl/3-phenylsulfonylpropiolate (135) is a superior dienophile to DMAD (Scheme 50). 

The scheme shows that the influence of substituents on CH acidity in ethynylpy-razoles is not additive as compared with benzene derivatives (84IZV923), and its value depends, for each substituent, on the nature of other groups in different positions of the azole. 

Treatment of 1,2,4-triazines 91a-91e with the electron-deficient die-nophile dimethyl acetylenedicarboxylate gave products, depending on the substituents [77LA( 10) 1718]. Pyrrolo-[2, -/][ ,2,4]triazines 92 were obtained via [4 + 2]-cycloaddition [77LA(9)1413, 77LA( 10)1718] with 91, but interaction with 91b in the absence of solvent gave, in addition to 92, the pyrido[2,l-/][l,2,4]triazine 93 and [l,3]oxazino[2,3-/][l,2,4]-triazine 94. In case of 91a pyridine and benzene derivatives were also formed in addition to 92 (Scheme 23). 

Moulijn et al. (33) studied the reactions of some linear alkynes over a W08-Si02 catalyst in a fixed-bed flow reactor. Besides metathesis, cyclotrimerization to benzene derivatives occurred. Thus, propyne yielded, in addition to metathesis products, a mixture of trimethylbenzenes. From this an indication of the mechanism of the metathesis of alkynes can be obtained. 

Charton, M., Prog. Phys. Org. Chem., 8, 235 (1971) has reported extensively on correlations of rate data for ortho substituted benzene derivatives using the dual substituent parameter treatment in the form with an additional (intercept) parameter, and in our opinion, too limited substituent data sets. For these and related reasons which we have discussed, we question the significance of many of Charton s correlations. 

Addition of molten sulfur to limonene in a 9 kl reactor led to a violent runaway exothermic reaction. Small scale pilot runs had not shown the possibility of this. Heating terpenes strongly with sulfur usually leads to formation of benzene derivatives with evolution of hydrogen sulfide. 

Although satisfactory for weak donor-acceptor Interactions, this model does not hold in the case of strong charge transfer such as happens in some disubstltuted benzene derivatives. A simple additive assumption falls short of the experimental values for the three nitroanllines in the para, ortho and meta positions (14). Discrepancies between an additivity assumption and experimental values are seen to Increase with the degree of conjugation Induced by the substituent relative locations. 

NbBrs, and NbCls-Pl Sn evidently proceeds via cyclotrimerization of diynes, which most probably involve cyclic carbometallation, details are not very clear.246 2463 Related reactions of Ta and Mo complexes were also investigated in this study. Formation of tantallacyclopropenes by complexation of alkynes with Ta complexes has also been reported247 (Scheme 51). In addition to the Ta-catalyzed polymerization of diynes mentioned above, Ta-catalyzed or -promoted cyclotrimerization reactions of alkynes to produce benzene derivatives, a Ta-promoted ethylene... 

The addition reactions of zirconacyclopentadienes to carbon—carbon triple bonds can be classified into two types (a) 1,1-addition reactions, and (b) 1,2-addition reactions, which furnish benzene derivatives as shown in Eq. 2.45. 

Addition to carbon carbon triple bonds Formation of benzene derivatives... 

Generally speaking, two mechanisms may be considered for the formation of benzene derivatives from metallacyclopentadienes. These are the concerted mechanism (Path A) and the insertion (addition) mechanism (Path B), as shown in Eq. 2.49. 

There are several examples of the concerted mechanism. However, no report of an insertion of a carbon—carbon triple bond into a metallacyclopentadiene had appeared prior to discovery of this reaction. At low temperatures, during the reaction of zirconacyclopentadienes with DMAD, the formation of trienes (79) is observed upon hydrolysis. This clearly indicates that the benzene formation involves the insertion (addition) reaction of DMAD. As shown in Eq. 2.50, the alkenyl copper moiety adds to the carbon—carbon triple bond of DMAD and elimination of Cu metal leads to the benzene derivatives 72. Indeed, a copper mirror is observed on the wall of the reaction vessel. 

However, at elevated temperatures, the disilene (/-Uu (Si)(k)SiSi( R)(Si/-Bu () 721 undergoes isomerization to give the 1,2-disilyl benzene derivative 730, which can be rationalized in terms of a C-H addition to the Si-Si double bond (Scheme 97). 

A recent report from the U. K. deals with 1,4-bis(oxodihydropyridazin-yl)benzenes and congeners which are also potent phosphodiesterase inhibitors and inodilators [159], This investigation, together with computer-aided modelling studies on various phosphodiesterase III inhibitors [160], may well stimulate the rational design of additional pyridazine-derived inodilators. 

As discussed, there are various methods of cation-radical generation. Every individual case needs its own appropriate method. A set of these methods is continuously being supplemented. For example, it was very difficult to prepare the cation-radicals of benzene derivatives with strong acceptor groups. However, some progress has been achieved, thanks to the use of fluorosulfonic acid, sometimes with addition of antimony pentafluoride, and lead dioxide (Rudenko 1994). As known, superacids stabilize cationic intermediates (including cation-radicals) and activate inorganic oxidants. The method mentioned is effective at -78°C. Meanwhile, -78°C is the boundary low temperature because the solution viscosity increases abruptly. This leads to the anisotropy of a sample and a sharp deterioration in the ESR spectrum quality. 

De Queiroz et al. (2006) performed mass-spectrometric experiments in which gas-phase reactions of the isolated N02 and benzene derivatives were studied. The reaction results in the predominant electron abstraction yielding exclusively ionized benzenes. None of the expected adducts (such as a complexes) were observed. Probably because direct addition of NO, to benzene is strongly exothermic, the nascent product is too hot to survive when it is isolated in the gas phase. 

Table 5.6 gives characteristic chemical shifts for the aromatic protons in benzene derivatives. To a first approximation, the shifts induced by substituents are additive. So, for example, an aromatic proton which has a -NO2 group in the para position and a -Br group in the ortho position will appear at approximately 7.82 ppm [(7.26 + 0.38(p-NO2) + 0.18(o-Br)]. 

The reaction of the chloro ester 1-Me with 1,2-dinucleophilic 1,2-disubstituted benzene derivatives 161 in most cases gave the benzene-annelated six-member-ed heterocycles 162 in moderate yield (Scheme 50) [22b, 26,73]. The course of the domino-Michael addition-cyclization is also very sensitive to the nature of the base and the reaction conditions applied. Thus, only the primary Michael adducts... 

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