Aromatic compounds, activation

Turro, N.J., Chow, M.-F., Rigaudyo, J., 1981. Mechanism of thermolysis of endoperoxides of aromatic compounds. Activation parameters, magnetic field, and magnetic isotope effects. J Am Chem Soc. 103, 7218-7222. 

Aromatic compounds activated by electron donating groups undergo photosubstitution preferentially in the ortho or para position (5.3) 503). 

In accordance with a typical electrophilic aromatic substitution, this reaction is successfully accomplished by simply treating aromatic compounds activated by electron-donating groups, such as alkoxy, phenoxy, hydroxyl and thiophenoxy moieties, with tellurium tetrachloride in reflnxing chloroform, carbon tetrachloride or tolnene. ° ... 

For aromatic compounds, activation energy increases as Hammett s constants decrease, as shown in Figures 10.21 and 10.22. Figure 10.21 shows the relation between these two parameters. The dataset of 2,4-dichlorophenol, ///-xylene, and phenol were used. 

Covalently-bound addition complexes have been shown to result from the reactions of a wide variety of aromatic compounds, activated by one or more nitro-groups, with bases or other nucleophilic species. In some cases di-adducts or tri-adducts are also formed by the addition of more than one molecule of base. There is considerable current interest in these adducts and this article will be concerned with their structures and stoichiometries and with the factors governing their stabilities. The second section deals with the spectroscopic and chemical studies which have been used in structural elucidations. Some general principles... 

Ferrocene behaves like an aromatic compound activated for electrophilic substitution reactions. Thus, only minor modifications of experimental procedures developed for aromatics are necessary to obtain ferrocene derivatives (a useful review on general methods is given by Schldgl and Falk [42]). For central chiral ferrocenes, resolution of the racemate is a frequently applied technique. Traditionally, resolutions are best achieved by salt formation between a chiral acid or base and the... 

Intermolecular reductive couplings between aromatic rings mostly involve either reactive aryl cr-radicals, for example, derived from aromatic halides by cleavage of the radical anions, or relatively stable 7r-radical anions derived from aromatic compounds activated by electron-withdrawing substituents. 

Dimerization of Aromatic Compounds Activated with Electron-Withdrawing Substituents... 

P205/Si02 was used for the solvent-free nitration of aromatic compounds. Activated aromatic compounds were converted into the corresponding nitro-aromatic compounds at room temperature under solvent-free conditions in excellent yields in 2-7 min, and deactivated aromatic compounds were converted into nitroben-zenes in moderate to good yields in 15-20 min [125],... 

In contrast to FADH2-dependent halogenases, haloperoxidases have no substrate specificity. The enzymatic iodination, bromination, and chlorination of a number of different aromatic compounds by haloperoxidases have been reported in the last few years. All aromatic substrates halogenated successfully by haloperoxidases are aromatic compounds activated for electrophilic substitution (Table 16.9-1). 

Synthesis of aromatic ethers has been performed under solvent-free phase-transfer catalysis conditions by reaction of several aryl halides with potassium methoxide or phenoxide in the presence of a catalytic amount of 18-crown-6. The specific MW effects were shown to be very dependent on the nucleophile and on the structure of the aromatic compound (activated or nonactivated, chloride or fluoride) (Eq. (56), Table 4.17) [96, 142]. 

Dibenzo and dinaphthotetrathiocines (116)-(123) are formed in polar solvents by reaction of disulfurdichloride with the appropriate aromatic compound activated by alkoxy substituents (Equation (28)) <89PS(42)111>. 

This reaction was first reported by Japp and Maitland in 1903. It is the acid promoted thermal condensation between arylhydrazine and aromatic compounds activated by a hydroxyl group to give carbazole derivatives. Therefore, this reaction is known as the Japp-Maitland condensation, or Maitland-Japp reaction. For example, the condensation between 6-alkyl-2-naphthols and phenylhydrazine affords 3-alkyl-7Jf-benzo-[c]carbazoles in good yield. However, due to the heat sensitivity of naphthylhydrazines and their salts, the condensation with naphthylhydrazines gives corresponding carbazoles in very low yields." In addition, the condensation with simple 2-naphthol also affords poor yields. ... 

A plethora of electron-deficient arenes can enter the VNS reaction carbocyclic and heterocyclic aromatic compounds activated by the nitro group and arenes that are active electrophiles due to their electronic configuration, such as azulene [35, 36], electron-deficient annulenes [37], tropylium cation [38], and particularly azines and azinium cations. Interestingly, q -transition metal complexes of arenes, such as benzene tricarbonylchromium, do not enter the VNS reactions. Although the addition of carbanions to these electron-deficient rings proceeds efficiently, and these adducts can be oxidized to form the products of ONSH, the p-elimination of HCl from the o adducts of a-halocarbanions does not occur [39, 40]. 

Naphthol is a highly nucleophilic aromatic compound, activated by resonance release from the phenolic oxygen. NaOH is a strong base, and CHCI3 possesses an acidic hydrogen, since the carbanion is stablised by electron withdrawl from the adjacent chlorine atoms. 

Meisenheimer complex (Section 14.12) The intermediate in nucleophilic aromatic substitution formed by the addition of a nucleophile to an aromatic compound activated by electron-withdrawing groups, often NO2. 

According to Olah [143], the formation of the jt-complexes with the aromatic compounds activated by donor substituents explains the paradox, known for this series, of the loss of substrate selectivity with simultaneous retention of the positional (regio) selectivity in the nitration and alkylation reactions. It is argued... 

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