Three Heterocyclic Rings Fused (6-5-6)

This review surveys heterocyclic systems (6:5:6) with ring junction heteroatoms reported from June 2006 to June 2019. Systematic names along with the corresponding literature references for 111 distinct ring systems with one ring junction nitrogen atom (Table 1) and 33 condensed heterocycles with two ring junction heteroatoms (Table 2) are provided. Further, the tricyclic fused compounds have been reviewed in terms of their theoretical and experimental structural characterization, chemical reactivity, as well as synthetic methods used for their preparation.