1.2.5- Oxadiazoles nomenclature

In this chapter, as in CHEC(1984) and CHEC-II(1996) <1984CHEC(6)393, 1996CHEC-II(4)229>, the chemistry of compounds with the 1,2,5-oxadiazole ring system is considered. The history and nomenclature of these compounds, as well as basic synthetic methods and chemical properties of 1,2,5-oxadiazoles reported before 1996, were reviewed previously . This chapter covers the period from 1996 to 2006. 

Tiemann and Kruger 114) who prepared the first 1,2,4-oxadiazoles proposed the name "azoximes . In their nomenclature, generally used in the older German literature, the carbon atoms in the ring are con-... 

In the remaining two chapters in the present volume, L. B. Clapp deals with 1,2,4-oxadiazoles, and A. D. McNaught has tackled the daunting task of explaining the intricacies of heterocyclic nomenclature. 

It should be pointed out that currently both trivial and systematic names are commonly used for naming the heterocyclic compounds. For example, an organic chemist will recognize without any difficulty the structures connected to names such as furane, pyrrole, pyrrolidine, pyrazole, imidazole, pyridine, or piperidine, despite the fact that all these names are trivial. On the other hand, the complex heterocycles require more sophisticated approaches in order to avoid ambiguity and correctly translate the chemical strucmre into the name. For these, compound names are often made using either trivial name (e.g., indazole for benzopyrazole, benzimidazole, indole, and isoindole) or the Hantzsch-Widman nomenclature, for example, 1,2,3- or 1,2,5-oxadiazoles, 1,3-dioxolane, 1,2- or 1,3-dithiolane, and 1,3- or 1,4-dioxane. It should be noted that the Hantzsch-Widman nomenclature treats the unsaturated heterocycle with maximum number of conjugated double bonds as parent compound. This adds another layer of complexity, giving rise to names such as... 

Two tandem [4 -I- 2]/[3 -I- 2] cycloadditions were highlighted one involves nitroalkenes and the other 1,3,4-oxadia-zoles. However, this nomenclature is an oversimplification. The tandem processes involving cycloadditions of nitroalkenes do not really end after the [3 + 2] cycloaddition step. The nitroso acetal hydrogenolysis is almost always an inevitable component of the process, intimately connected to the cycloadditions with the common objective—to create polycyclic amines. Therefore, the more accurate name of such processes should be tandem [4 - - 2]/[3 - - 2]/hydrogenolysis. On the other hand, the tandem cycloaddition of 1,3,4-oxadiazoles involves an intervening extmsion of dinitrogen, which is a retro-[3 + 2] cycloaddition. Therefore, the more accurate name is tandem [4 -I- 2]/retro-[3 -I- 2]/[3 -I- 2] cycloaddition. 

---