A tender-hearted Pd­(II)-catalyzed C–H activation of 1-arylindazolones followed by an oxidative [4 + 2] annulation reaction has been accomplished, engaging allenoates as annulating partners. Using this strategy, two different regioisomeric forms of cinnoline-fused indazolones possessing internal and exocyclic double bonds were synthesized in acetic acid and dioxane, respectively. Mild and aerobic conditions, avoiding the use of any metal–oxidant, highlights the rewards of this oxidative annulation protocol.

Ru(II)-catalyzed strategies were developed for the [4+1] and [4+2] oxidative coupling between N-aryl-2,3-dihydrophthalazine-1,4-diones and 1,4-benzoquinones, achieving spiro-indazolones and fused-cinnolines, respectively. Mild, aerobic and external oxidant-free conditions, and the use of...

Regioselective C-arylation and C,N-diarylation in 2-aryl-2,3-dihydrophthalazine-1,4-diones have been successfully accomplished with diaryliodonium salts under base-mediated slightly modified Pd-catalyzed conditions. These ligand-driven transformations provided a variety of diversely decorated bi(hetero)aryls in good-to-excellent yields, while N-arylated product could be obtained under similar Pd-catalyzed conditions in absence of a ligand.