7. Quinolines and Isoquinolines
Heterocyclic Chemistry at a Glance, Second Edition. John A. Joule and Keith Mills.
© 2013 John Wiley & Sons, Ltd. Published 2013 by John Wiley & Sons, Ltd.
Electrophilic addition to nitrogen
Most of the chemistry of quinoline parallels that of isoquinoline so in this chapter we use examples from each series,
more or less randomly. The benzene rings and the pyridine rings of quinoline and isoquinoline each display the reactiv-
ity typical of these monocyclic systems, but modifi ed, in some cases, by the presence of the other ring. Thus, in processes
exactly like those for pyridine, electrophiles add to the heterocyclic nitrogen – reaction with acids or electrophilic halides
gives quinolinium and isoquinolinium salts, or with peracids, N-oxides.
Electrophilic substitution at carbon
As we reminded ourselves (pages 10–11), electrophilic substitution is the typical reaction of benzene compounds. We
also learnt that pyridines, without activating substituents, are very resistant to electrophilic C-substitution (pages 12
and 34). In quinolines and isoquinolines, then, it is no surprise that standard electrophilic substitutions occur exclu-
sively on the benzene ring. Further, and recalling the propensity for naphthalene to be attacked most rapidly at the
1-position, such electrophilic substitutions of quinolines and isoquinolines take place only at the 5- and 8-positions.
It is important to realise that these substitutions probably involve attack on quinolinium and isoquinolinium cations.
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Quinolines and Isoquinolines