Tetrahydroxydiboron-mediated metal-free synthesis of 2H-indazoles via reductive heterocyclization.

A concise, efficient, green, and metal-free reductive heterocyclization reaction has been established for the construction of 2H-indazoles. With low-toxic, eco-friendly tetrahydroxydiboron serving as the reducing agent, this protocol exhibits a broad substrate scope, affording diverse 2H-indazoles with yields ranging from 10% to 90%. This synthetic route was used to prepare pharmacophoric fragment 4d, and molecular docking simulations proved its potential as a potent hERG inhibitor.