Six-membered Nitrogen-containing Rings

The current volume consists of four chapters. It commences with a comprehensive survey of the conformational rates and equilibria of saturated nitrogen-containing six-membered rings, authored by T. A. Crabb and the series editor. This is a subject wherein many of the past controversies have now been resolved and where it is now possible to provide a rather satisfying account. 

This review, which complements an earlier one (Part I) dealing with transition metal complexes of triazenes, tetrazenes, tetraazadienes, and pentaazadienes, examines the coordination chemistry of related cyclic catenated nitrogen ligands. Six-membered rings containing three, four, or five adjacent nitrogen atoms — 1,2,3-triazines, 1,2,3,4-tetrazines, and pentazines, respectively — are either unknown or are relatively unstable species whose coordination chemistry has yet to be explored. 

Herbicides are used to kill plants. Sodium chlorate, NaC103 and sodium arsenite, Na3As03, were commonly used as weed killers in the first half of the twentieth century, but inorganic arsenic compounds, in particular, are toxic to mammals. Organic herbicides are now used. They are much more toxic to certain types of plants than to others, so they can be used as selective weedkillers. Atrazine, which is a member of a class of herbicides called the triazines, is widely used to kill weeds in cornfields. The triazines contain six-membered rings with alternating carbon and nitrogen atoms. The effects of atrazine on human health are not yet clear. 

Pyridine is the six-membered ring heterocycle containing one nitrogen. Three six-membered ring molecules contain two nitrogen atoms—pyrazine (1,4 N), pyrimidine (1,3 N), and pyridazine (1,2 N) 4, 5, 41, 42. 

In spite of the diverse nature of alkaloid structures, two structural units, i.e. fused pyrrolidine and piperidine rings in different oxidation states, appear as rather common denominators. We therefore chose to give several examples for four types of synthetic reactions which have frequently been used in alkaloid total synthesis and which provide generally useful routes to polycyclic compounds with five- or six-membered rings containing one nitrogen atom. These are ... 

Part 2 (Volumes 2 and 3) deals with mono- and poly-cyclic compounds with one or more six-membered heterocyclic ring, with nitrogen, oxygen and sulfur as the heteroatoms. Volume 2 contains the six-membered rings with one nitrogen atom (Part 2A) and Volume... 

The separate stems for three-, four- and five-membered rings containing nitrogen are used for historical reasons. Those for the different groups of six-membered rings are... 

Freudenberg has obtained one nitrogen-free product, C13H24O, b.p. 215-220°, by the distillation of aconitine or amorphous aconitine with barium hydroxide or zinc dust. He suggests that the fundamental hydrocarbon, C20H33, may contain two five-membered and four six-membered rings, which will include nine secondary carbon atoms. 

If a six-membered ring contains two or more nitrogen atoms, the... 

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