A Novel Copper-Catalyzed, Hydrazine-Free Synthesis Of N-1 Unsubstituted 1h-Indazoles Using Stable Guanylhydrazone Salts As Substrates

A CuI-catalyzed, hydrazine-free transformation of 2-(2-bromoarylidene)guanylhydrazone hydrochlorides using Cs2CO3 as a base and DMEDA as a ligand at 120 degrees C for 5 h delivers substituted 1H-indazoles with yields up to 75%. The C,N double bond configuration of the substrates was determined by NMR experiments and quantum chemical calculations. The reaction mechanism was studied using quantum chemical calculations. (C) 2021 Elsevier Ltd. All rights reserved.