Synthesis of 3C-alkylated active methylene substituted 2H-indazole derivatives via sequential ring opening of donor–acceptor cyclopropanes and reductive cyclization reaction

Abstract

A concise sequential protocol is developed to synthesize 3C-alkylated active methylene substituted 2H-indazole derivatives via a nucleophilic ring opening reaction (NRO) of o-nitro donor–acceptor cyclopropanes (DACs) with primary arylamines catalyzed by Ni(ClO₄)₂·6H₂O followed by a SnCl₂·2H₂O-mediated intramolecular reductive cyclisation. The di-ester functionality can be transformed into the corresponding monoesters, acids, alcohols and amides that form the core units of important biologically active molecules.