Electrophilic aromatic substitution polycyclic compounds

A number of aromatic compounds undergo nucleophilic substitution, while electrophilic photosubstitution on aromatic ring is rare. The photosubstitution is very conventially done on monocyclic, polycyclic and heterocyclic aromatic... 

Polycyclic aromatic compounds also undergo electrophilic aromatic substitution reactions. Because the aromatic resonance energy that is lost in forming the arenium ion is lower, these compounds tend to be more reactive than benzene. For example, the brotni-nation of naphthalene, like that of other reactive aromatic compounds, does not require a Lewis acid catalyst ... 

The fluorination of aromatic compounds with xenon difluoride has been extensively investigated.180- 188 The fluorination of benzene with xenon difluoride in the presence of hydrogen fluoride as a catalyst results in the formation of fluorobenzene in 68% yield.180 Monosub-stituted aromatic systems are reported to give high yields of monofluorinated compounds, the isomer distributions of which are similar to those observed in electrophilic substitution (Table 14).181 Alkylaromatics, benzocyclenes and polycyclic aromatics are all successfully fluorinated by xenon difluoride in the presence of hydrogen fluoride examples are the fluorination of 21,182 22,182 23,184 185 24,185 and 25.182... 

Polycyclic aromatic compounds such as naphthalene, anthracene, and phenanthrene give electrophilic aromatic substitution reactions. The major product is determined by the number of resonance-stabilized intermediates for attack at a given carbon and the number of fully aromatic rings (intact rings) in the resonance structures. 

Substituents such as alkene units, alkyne units, and carbonyls can be reduced by catalytic hydrogenation. Lithium aluminum hydride reduces many heteroatom substituents, including nitrile and acid derivatives 56, 57, 104, 105, 106, 107, 108, 109. Polycyclic aromatic compounds such as naphthalene, anthracene, and phenanthrene give electrophilic aromatic substitution reactions. The major product is determined by the number of resonance-stabilized intermediates for attack at a given carbon and the number of fully aromatic rings (intact rings) in the resonance structures 59, 60, 61, 62, 63, 64, 65, 85, 104, 106, 107, 108,109,110,113,114,118. 

As described earlier, the S Ar involves the reaction of an electrophilic species with an arene nucleophile. There are several types of arenes common to the S Ar reactions substituted benzenes, polycyclic aromatic compounds, and heterocyclic compounds. Substituent effects largely control the chemistry of substituted benzenes and related compounds. This includes both activating and directing effects of substituents on the S Ar reaction. 

The nitration of polycyclic aromatic compounds by NO is analogous to aromatic substitution by other electrophilic radicals. The mechanism involves a rate-determining O-complex formation. This is illustrated in the following scheme using anthracene as the representative compound [40] ... 

Electrophilic aromatic substitution is a general reaction of all aromatic compounds, including polycyclic aromatic hydrocarbons, heterocycles, and substituted benzene derivatives. A substituent affects two aspects of electfophilic aromatic substitution ... 

Substituted benzene compounds belong to a class of conjugated compounds called arenes. Examples include benzene, naphthalene, anthracene, and phenanthrene. The common structural feature of arenes is a monocyclic or polycyclic system of k electrons that results in a special stability called aromaticity. As a result, aromatic compounds are much less reactive in electrophilic addition reactions than we would expect based on the reactivity of polyenes. 

Electrophilic substitution of polycyclic aromatic compounds is generally faster than that of benzene, because they have lower aromatic stabilization. 

The gold-catalyzed reaction of alkynes with aromatic units has been extensively studied [105-107]. This reaction allows the synthesis of polycyclic aromatic and heteroaromatic systems via Friedel-Crafts-type processes. Although, the C-H activation of aryl compounds by gold(lll) has been known for more than 70 years, it is accepted that the Friedel-Crafts-type reaction proceeds via [Au(alkyne)] complexes and subsequent electrophilic aromatic substitution with the arenes or heteroarene compounds. 

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