Bicyclic 5-6 Systems with One Bridgehead (Ring Junction) Nitrogen Atom: Three Extra Heteroatoms 2:1

Abstract

The chemical behavior of 45 various bridgehead nitrogen atom-containing fused ring systems with two extra heteroatoms in the five-membered ring and one extra heteroatom in the six-membered ring, including their benzologues, is reviewed. The six-membered ring components are oxazines, thiazines, pyridazines, pyrimidines, and pyrazines, whereas the five-membered fused rings contain nitrogen, oxygen, sulfur, selenium, and phosphorus atoms in various positional arrangements. Among structural investigations, semi-empirical theoretical calculations, 13 C NMR and 15 N NMR spectroscopic investigations, and mass spectral studies are reviewed. The reactivities are categorized in three main groups: (1) transformations of the whole rings, for example, ring transformation, ring oxidations, cycloadditions, etc.; (2) chemical reactions at one of the ring carbons or heteroatoms, for example, substitutions, oxidation of ring heteroatoms, etc.; and (3) transformations of the substituents. A substantial amount of research on synthesis of the particular ring systems is summarized. The novel applications of established earlier recognized methodologies are compiled mostly in tables containing references. Novel cyclization reactions are treated in more detail, and in the most interesting cases the reaction mechanism is also discussed. Finally, a table reveals biological properties of 10 important derivatives.