Rhodium(III)‐Catalyzed Dehydrogenative Annulation of 2‐Arylindazoles with Cyclic Enones

Ir(III)-Catalyzed Dual C-H Activation of 2-Aryl Phthalazinediones and 3-Aryl-2H-benzo[e][1,2,4]thiadiazine-1,1-dioxides for the Construction of Spiro-Fused Cyclic Frameworks

An Ir(III)-catalyzed double C-H activation strategy has been developed for the synthesis of highly rigid spiro frameworks by means of ortho-functionalization of 2-aryl phthalazinediones and 2,3-diphenylcycloprop-2-en-1-ones using the Ir(III)/AgSbF₆ catalytic system. Similarly, 3-aryl-2H-benzo[e][1,2,4]thiadiazine-1,1-dioxides undergo smooth cyclization with 2,3-diphenylcycloprop-2-en-1-ones to afford a diverse range of spiro compounds in good yields with excellent selectivity. Additionally, 2-arylindazoles provide the corresponding chalcone derivatives under similar reaction conditions.

Recent advances in C-H functionalization of 2H-indazoles

2H-Indazoles are one class of the most important nitrogen-containing heterocyclic compounds. The 2H-indazole motif is widely present in bioactive natural products and drug molecules that exhibit distinctive bioactivities. Therefore, much attention has been paid to access diverse 2H-indazole derivatives. Among them, the late-stage functionalization of 2H-indazoles via C-H activation is recognized as an efficient approach for increasing the complexity and diversity of 2H-indazole derivatives. In this review, we summarized recent achievements in the late-stage functionalization of 2H-indazoles, including the C3-functionalization of 2H-indazoles through transition metal-catalyzed C-H activation or a radical pathway, transition metal-catalyzed ortho C2'-H functionalization of 2H-indazoles and remote C-H functionalization at the benzene ring in 2H-indazoles.

Rediscovering Bacon's hydrazine/phenylhydrazine mediated cyclization of 2,2'-dicarbonylbi(hetero)aryls: construction of (5-azo)-/indazolo[2,3-a]quinolines

Hydrazine/phenylhydrazine-mediated reductive dicarbonyl coupling reactions have been carried out under mild conditions to provide polycyclic aromatic compounds and azo-substituted polyaromatic compounds. This method has a broad substrate scope with good functional group compatibility.