Recent Strategies in Transition-Metal-Catalyzed Sequential C–H Activation/Annulation for One-Step Construction of Functionalized Indazole Derivatives

Abstract

Designing new synthetic strategies for indazoles is a prominent topic in contemporary research. The transition-metal-catalyzed C–H activation/annulation sequence has arisen as a favorable tool to construct functionalized indazole derivatives with improved tolerance in medicinal applications, functional flexibility, and structural complexity. In the current review article, we aim to outline and summarize the most common synthetic protocols to use in the synthesis of target indazoles via a transition-metal-catalyzed C–H activation/annulation sequence for the one-step synthesis of functionalized indazole derivatives. We categorized the text according to the metal salts used in the reactions. Some metal salts were used as catalysts, and others may have been used as oxidants and/or for the activation of precatalysts. The roles of some metal salts in the corresponding reaction mechanisms have not been identified. It can be expected that the current synopsis will provide accessible practical guidance to colleagues interested in the subject.

Recent Strategies in Nickel-Catalyzed C–H Bond Functionalization for Nitrogen-Containing Heterocycles

“…Recently, some related reviews on transition metal-catalyzed C−H functionalization for the construction of diverse nitrogen-containing heterocycles have been reported [34][35][36][37][38][39][40][41]. However, most of them focused mainly on Pd, Rh, Co, and Cu catalysts [34][35][36][37][38][39][40]; only one report from the Cramer group briefly illustrated their Ni-catalyzed asymmetric C-H bond functionalization for chiral N-heterocycles [41].…”

“…Recently, some related reviews on transition metal-catalyzed C−H functionalization for the construction of diverse nitrogen-containing heterocycles have been reported [34][35][36][37][38][39][40][41]. However, most of them focused mainly on Pd, Rh, Co, and Cu catalysts [34][35][36][37][38][39][40]; only one report from the Cramer group briefly illustrated their Ni-catalyzed asymmetric C-H bond functionalization for chiral N-heterocycles [41]. In this review, we will briefly introduce the recent progress in the field of nickel-catalyzed N-heterocycle synthesis by C-H functionalization via intramolecular and intermolecular pathways, respectively (Figure 1).…”