Heteroannulation Routes to Bioactive Pyrazolooxazines

Pyrazolo-oxazine fused systems are interesting classes of heterocyclic compounds exhibiting pronounced biological applications such as anticancer, antitubercular, anti-inflammatory, antibacterial and antifungal activities as well as inhibiting COX-1 and COX-2 enzymes. Depending on the distribution position of the heteroatoms (N and O), there are fourteen different systems of pyrazolo-oxazine. Nine of them were biologically abundant in literature, for example, pyrazolo[3,4-e][1,3]oxazines are used as analogs of antibiotics Formycin, Formycin B, Oxoformycin B. This review article summarizes the concerted efforts expended on most of the synthetic routes to the various types of pyrazolo-oxazines in the literature until the first quarter of 2020. The reactions of pyrazolo-oxazines with various reagents are also outlined.