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

Abstract

The chemical behavior of 43 bridgehead nitrogen atom-containing bicyclic heterocycles is reviewed. These ring systems contain one extra heteroatom in the five-membered ring and two extra heteroatoms in the six-membered ring – or the reverse. Among the structure elucidation results, 15N- and 13C NMR data for numerous derivatives are provided and X-ray structure determinations are summarized. The reactivities of the various ring systems are classified according to ring openings (involving also ring transformations), ring contractions, formation of further fused rings, cycloadditions, electrophilic and nucleophilic substitutions, and cross-couplings. Recently recognized transformations are discussed in more detail, whereas applications of earlier established methodologies for preparation of new derivatives are summarized. The ring syntheses leading to this large group of ring systems are classified according to the six-membered component of the fused heterocycle. Relatively little information is available for azolo-fused oxadiazines, dithiazines, thiadiazines, oxazaphosphinines, and diazaphosphinines. In contrast to these ring systems, a substantial amount of synthetic work is reviewed for fused [1,3,5]triazines and [1,2,4]triazines. In the sections describing the cases of the various fused triazines, the ring-closure procedures according to the different five-membered rings are reviewed in separate subsections. The biological importance of some outstanding derivatives is also pointed out.