Synthesis of Aromatic Heterocycles

This chapter shows how just a few general principles allow one to understand the methods, at first sight apparently diverse, which are used in the construction of the heterocyclic ring of an aromatic heterocyclic compound from precursors which do not have that ring. It discusses the principles, and analyses the types of reaction frequently used in constructing an aromatic heterocycle, and also the way in which appropriate functional groups are placed, in the reactants, in order to achieve the desired ring synthesis. 

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Our study of heterocyclic compounds is directed primarily to an understanding of their reactivity and importance in biochemistry and medicine. The synthesis of aromatic heterocycles is not, therefore, a main theme, but it is useful to consider just a few examples to underline the application of reactions we have considered in earlier chapters. From the beginning, we should appreciate that the synthesis of substituted heterocycles is probably not best achieved by carrying out substitution reactions on the simple heterocycle. It is often much easier and more convenient to design the synthesis so that the heterocycle already carries the required substituents, or has easily modified functions. We can consider two main approaches for heterocycle synthesis, here using pyridine and pyrrole as targets. 

Diketene also is widely employed as a natural and synthetic fiber cross-linking agent, wood preservative and paper-sizing agent. Both it and /3-propiolactone have wide application as chemical intermediates. The synthetic applications of diketene for the synthesis of aromatic, heterocyclic and aliphatic compounds is exceptionally extensive (74ACR265). 

Summary the three major approaches to the synthesis of aromatic heterocycles... 

A. Rauf and N. N. Farshori, Microwave-Induced Synthesis of Aromatic Heterocycles, SpringerBriefs in Green Chemistry for Sustainability, DOI 10.1007/978-94-007-1485-4 l, The Author(s) 2012... 

DIastereoselectIvlty ch33-ch34 Pericycllc reactions ch35-ch36 Synthesis of aromatic heterocycles ch44... 

Synthesis of aromatic heterocycles , Gilchrist, T. L., J. Chem. Soc., Perkin Trans. I, 1999, 2849, and previous reviews in the series. 

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