Ru(II)-catalyzed C–H activation with diazo compounds for the sustainable synthesis of N-heterocycles

Diazo compounds represent a versatile and readily accessible class of reagents in modern organic synthesis, serving as valuable carbene precursors for a broad spectrum of transformations owing to their high reactivity and facile preparation. In recent years, Ru(II)-catalyzed C–H activation reactions employing diazo compounds have emerged as a powerful strategy for the construction of nitrogen-containing heterocycles. This review highlights recent advances in Ru(II)-catalyzed C–H activation, Ru-carbene formation, carbene migratory insertion, and annulation processes using diazo compounds, focusing on their application to the efficient and sustainable synthesis of diverse nitrogen heterocyclic scaffolds such as indoles, 3 H -indoles, indazolone-fused cinnolines, isoquinolines, 8 H -isoquinolino[1,2- b ]quinazolin-8-ones, isoquinolinones, quinoxalines, azacoumestans, indolines, spiroindolinones, and benzoindoles.