Synthesis of Phthalazino[2,3‐a]cinnoline‐6,8,13(5H)‐triones via Ir(III)‐catalyzed Dehydrogenative C‐H/N‐H Functionalization of N‐aryl Phthalazinones

An Iridium(III)‐catalyzed C−H cyclization of N‐arylphthalazinones with α‐diazotized Meldrum's acid afforded tetracyclic phthalazine derivatives with a carbonyl group in 98% yield in only 30 min. The initial formation of tetracyclic phthalazine derivatives also provided access to a powerful building block. The utility of this method is emphasized by the synthetic transformation into a series of potentially bioactive derivatives.