Reactivity of Aromatic Heterocycles

This chapter describes in general terms the types of reactivity found in the typical six-and five-membered aromatic heterocycles. In addition to discussions of classical substitution chemistry, considerable space is devoted to radical substitution, metallation and palladium-catalysed reactions, since these areas have become very important in heterocyclic manipulations. In order to gain a proper appreciation of their importance in the heterocyclic context we provide an introduction to these topics, since they are only poorly covered in general organic text-books. Emphasis on the typical chemistry of individual heterocyclic systems is to be found in the summary/revision chapters (4, 7, 10, 12, 16, and 20) and a more detailed examination, of typical heterocyclic reactivity, and many more examples for particular heterocyclic systems are to be found in the chapters - Pyridines reactions and synthesis etc. For the advanced student, it is recommended that this present chapter should be read in its entirety before moving on to the later chapters, and that the introductory summary/revision chapters, like Typical reactivity of pyridines, quinolines and isoquinolines should be read before the more detailed discussions. 

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Our contribution to the reactivity of aromatic heterocycles involves only two papers [136], In the first one, we carried out IRC calculations (HF/6-31G ) to confirm the connecting structures of each transition state for the 1,2,3-triazole/iminodia-zomethane isomerizations. For the triazolate anion, both tautomers of 1,2,3-triazole and several 1,2,3-triazolium cations were studied. The below structure reports the case of the neutral molecules 30a and 30b. 

A new approach that we would like to introduce here to evaluate the reactivity of aromatic heterocycles that have asymmetric transition state structures is a comparison of the changes of the ring bond order between the heterocycle and... 

Table Relative reactivities of aromatic heterocycles towards [Fe(CO)3( j -C6H7)]-[BF4] at 45 °C from ref. 26)...

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