Cyclization of Azobenzenes Via Electrochemical Oxidation Induced Benzylic Radical Generation

Abstract

An electrochemical oxidation-induced cyclization of ortho-alkyl-substituted azobenzenes has been developed. The direct electrochemical benzylic C–H functionalization with respect to azobenzenes could proceed in the absence of any catalyst or external chemical oxidant to afford a number of 2H-indazole derivatives in moderate to good yields. This protocol enables the reuse of the byproduct to the same 2H-indazoles, thus significantly reducing pollution discharge in synthetic chemistry.

Visible Light-Mediated Heterodifunctionalization of Alkynylazobenzenes for 2H-Indazole Synthesis

“…2 H -Indazoles constitute prevalent structural motifs in bioactive natural products, , and drugs such as niraparib and pazopanib (Figure b) and 2-aryl indazoles exhibit interesting spectrophotometric properties . Their preparation from alkynylazobenzenes has been reported using transition metals such as Pd/Cu , and Rh or sensitive reagents such as TBAF. , No examples reporting the synthesis of 2 H -indazoles in the absence of a catalyst or excess of additives have been published to date. Considering their applications, it is of paramount importance to have new and general environmentally sustainable procedures in organic synthesis that reduce the cost of energy.…”

“… 22 Their preparation from alkynylazobenzenes has been reported using transition metals such as Pd/Cu 16 , 17 and Rh 23 or sensitive reagents such as TBAF. 24 , 25 No examples reporting the synthesis of 2 H -indazoles in the absence of a catalyst or excess of additives have been published to date. Considering their applications, it is of paramount importance to have new and general environmentally sustainable procedures in organic synthesis that reduce the cost of energy.…”

Electrochemical Cyclization of o-Aminyl Azobenzenes: Roles of Aldehydes in N–N Bond Cleavage

“…The transformation of classic azobenzenes often involves azo units to enable the generation of hydroazobenzenes, without allowing easy access to arylamines. , Furthermore, these early findings do not show the inherent value of azobenzene in synthetic chemistry. In recent years, azobenzenes have emerged as important starting materials for accessing a range of useful molecular compounds. − As such, methods for azobenzene functionalization have been developed by synthetic chemists.…”