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Volume 12: Five-Membered Hetarenes with Two Nitrogen or Phosphorus Atoms |
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Introduction by Prof. Reinhard Neier (Volume Editor): |
This volume covers the synthesis of five-membered heterocyclic compounds with either two nitrogen or phosphorus atoms or five-membered heterocycles containing both one nitrogen and one phosphorus atom. In accordance with the common principle of the series, the benzoannulated systems are treated directly after the monocyclic systems. The indazoles and benzimidazoles, the benzoannulated systems of pyrazoles and imidazoles, are so important that they are treated in separate chapters. In fusing a five-membered heterocycle containing two heteroatoms to a six-membered ring, one of the heteroatoms can be common to both rings. For these systems, the heterocyclic systems and their analogues containing one or more heteroatoms in the six-membered ring were combined in the same chapter, as long as the synthesis of these compounds proceeded via a ring-closure of the five-membered ring. The same rule was observed for the phosphorus and arsenic analogues:the azaphospholes, the azaarsoles, and the diphospholes.
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Most of the ring systems covered in Volume 12 are stable compounds, in accordance with the goals set for Science of Synthesis. The phosphorus and arsenic containing heterocycles are the most sensitive class of compounds treated in this volume. It is obvious, alone from the size of the chapters treating the different classes of heterocycles, that the knowledge and the number of synthetic procedures vary widely. Some of the heterocyclic rings were first synthesized almost 150 years ago like the imidazole ring (H. Debus 1858). The structures of the parent five-membered heterocycles were proven 120 years ago (imidazole: B. Radziszewski 1882, F. R. Japp 1886, and W. Marckwald 1889; pyrazole: L. Knorr 1887). In contrast to these compound classes, which have a rich history, the first member of the diphospholes was first reported just over 20 years ago (Issleib 1981) and the newest member of this family, the 1,2-diphosphole, only appeared in 1996 (Schmidpeter). Since the chemistry of imidazopyridines, pyrazolopyridines, imidazole, benzimidazole, pyrazole, and indazole has been worked on for the longest time, the chapters dedicated to these hetarenes are by far the largest ones in thisvolume. |
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