Cu^II–hydrotalcite catalyzed one-pot three component synthesis of 2H-indazoles by consecutive condensation, C–N and N–N bond formations

Abstract

An efficient and straightforward synthesis of 2H-indazoles is achieved from 2-bromobenzaldehydes, primary amines and sodium azide through consecutive condensation, C–N and N–N bond formations, catalyzed by a novel heterogeneous CuII–HT catalyst. The recoverable heterogeneous CuII–HT catalyst exhibited an impressive activity for the title reaction without any additives (expensive ligands, etc.). Heterocyclization proceeds through C–N and N–N bond formation, which is the key step to deliver the desired 2H-indazole scaffold. A series of structurally diverse 2H-indazoles were prepared in good to excellent yields from easily accessible starting materials by employing this protocol.