Bicyclic 6-6 Systems: Other Four Heteroatoms 2/2

Abstract This chapter describes the theoretical studies, synthesis, reactivities and potential applications of bicyclic 6-6 systems (excluding pteridines) containing four heteroatoms (N, O, S) without any at the cyclic junction. Thus, work published since 2008 on various series such as pyrazinopyrazine, pyrimidopyrimidine, pyridazinopyridazine, pyrazinopyridazine, pyrimidopyridazine, pyridazinooxazine, pyrimidooxazine, pyrazinooxazine, pyridazinothiazine, pyrimidothiazine, pyrazinothiazine and oxazinooxazine are discussed.