Regiochemistry electrophilic aromatic substitution

ArH Aromatic rings PhOR PhH PhCl PhCOR A donor on the ring makes it more reactive ewg makes ring less reactive. Electrophilic aromatic substitution. Regiochemistry of addition Hetero- aromatics, condensed aromatics... 

Presumably, the oxidative cyclization of 3 commences with direct palladation at the a position, forming o-arylpalladium(II) complex 5 in a fashion analogous to a typical electrophilic aromatic substitution (this statement will be useful in predicting the regiochemistry of oxidative additions). Subsequently, in a manner akin to an intramolecular Heck reaction, intermediate 5 undergoes an intramolecular insertion onto the other benzene ring, furnishing 6. (i-Hydride elimination of 6 then results in carbazole 4. 

Predicting the Effect of a Substituent on the Rate and Regiochemistry of an Electrophilic Aromatic Substitution Reaction... 

Table 17.1 Effect of Substituents on the Rate and Regiochemistry of Electrophilic Aromatic Substitution Reactions...

Predict the effect of these substituents on the rate and regiochemistry of electrophilic aromatic substitution reactions ... 

Aromatic compounds undergo many reactions, but relatively few reactions that affect the bonds to the aromatic ring itself. Most of these reactions are unique to aromatic compounds. A large part of this chapter is devoted to electrophilic aromatic substitution, the most important mechanism involved in the reactions of aromatic compounds. Many reactions of benzene and its derivatives are explained by minor variations of electrophilic aromatic substitution. We will study several of these reactions and then consider how substituents on the ring influence its reactivity toward electrophilic aromatic substitution and the regiochemistry seen in the products. We will also study other reactions of aromatic compounds, including nucleophilic aromatic substitution, addition reactions, reactions of side chains, and special reactions of phenols. 

Predict the effect of a substituent on the rate and the regiochemistry of an electrophilic aromatic substitution reaction. 

Directed metallation features in the synthesis of xanthones from diaryl ether amides under mild conditions and with a regiochemistry complementary to that of electrophilic aromatic substitution <97SL1081>. 

Working with the Concepts Predicting Regiochemistry in Electrophilic Aromatic Substitutions... 

Electrophilic substitution in the azoles is intermediate in facility between pyridine on the one hand and pyrroles, thiophenes and furans on the other the presence of the electron-withdrawing imine unit has an effect on the flve-membered aromatic heterocycles just as it does when incorporated into a six-membered aromatic framework, i.e. the comparison is like that between benzene and pyridine (Chapter 7). The order of reactivity - pyrrole > furan > thiophene - is echoed in the azoles, though the presence of the basic nitrogen complicates such comparisons. The regiochemistry of electrophilic attack can be rationalised nicely by comparing the character of the various ring positions - those that are activated in being flve-membered in character and those that are deactivated by their similarity to a- and y- positions in pyridine. 

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