Combined Gold and Photoredox Catalysis: Synthesis of 3-Alkenyl-2H-Indazoles from 2-Alkynylazobenzenes

Abstract

We disclose the intramolecular synthesis of 3-alkenyl-2<i>H</i>-indazoles from 2-alkynylazobenzenes promoted by a dual catalysis using AuCl3 and a ruthenium photocatalyst under irradiation with visible light. This reaction goes through a hydroamination of the alkynyl fragment. The yields are governed by the electronic factors. Control experiments and DFT calculations suggest that a radical and polar mechanisms are operating in parallel. This transformation goes through first formation and C-N bond and 1,2-hydride shift. Derivatization was also carried out to extend the versatility of this methodology.