Synthesis of Benzazoles through Electrochemical Oxidative Cyclization Reactions

Abstract

An effective method for the synthesis of benzazoles through the electrochemical oxidative cyclization of o-aminophenol/oaminothiophenol/o-phenylenediamine and aldehydes was developed. A series of benzazoles were efficiently synthesized by using this method in good yields. Furthermore, this method was applied to the synthesis of the drug thiabendazole in a gram-scale reaction, which proved the practicality of the method. This approach avoids using catalysts and oxidants, and has the advantages of wide substrate range, mild reaction conditions and good tolerance of functional groups. Finally, the possible reaction mechanism was proposed and supported by cyclic voltammetry (CV) and control experiments.

Non-metal-mediated N-oxyl radical (TEMPO)-induced acceptorless dehydrogenation of N-heterocycles via electrocatalysis

“… 15 Afterwards, as shown in pathway 1, 6a can readily react with 1a to obtain the imine D1, then imine D1 is converted to E1 which is oxidized (dehydrogenated) to afford the desired product 3aa via a radical-cation intermediate F1. 16 Similarly, hexagonal nitrogen-containing heterocyclic ring 6a also works well in the same way as shown in pathway 2. 17 …”

Electrochemical C–H Arylation of Quinazolinone with Aryl Tetrafluoroborate Diazonium Salts in Aqueous Solution of Ionic Liquids

“…When the ratio of [EMIM]­BF 4 was increased or [EMIM]­BF 4 was used as the reaction solvent, the reaction yields all decreased (Table , entries 20–21). When the constant currents of the reaction were changed, the product yields dropped to 65% and 54%, respectively (Table , entries 21–22), which may be due to the side reaction . Therefore, the best suitable current for the system was the constant current of 6.0 mA.…”

“…When CH 3 OH, THF, DMF, DMSO, DCE, and 22), which may be due to the side reaction. 46 Therefore, the best suitable current for the system was the constant current of 6.0 mA. In addition, we screened the reaction temperature and found that the yield of 3a was slightly decreased as the temperature increased (Table 1, entry 3 c ).…”

Fe‐Catalyzed Electrochemical C−O Bond Cleavage of Ethers to Access Benzazoles from Ethers and o‐Substituted Anilines

“…Organic electrosynthesis has been recognized as an environmentally friendly and enabling synthetic tool, in which electrons can be used instead of toxic or dangerous redox agents. [10] In these context, a variety of methodologies, such as electrochemical oxidative cyclization of o-aminothiophenol and aldehydes, [11] electrooxidative cyclization of benzylideneaminothiophenols, [12] electrochemical decarboxylative coupling of α-keto acids and 2-aminobenzenethiol, [13] electrochemical combination of aryl isothiocyanates with amines, [14] electrochemical cyclocondensation of alcohols and 2aminobenzenethiol, [15] and electrochemical oxidative cyclization of N-arylthioamides, [16][17][18] were developed for constructing benzothiazoles. However, it is noticed that the electrochemical synthesis of benzothiazoles by the reaction between ethers and 2-aminobenzenethiol has not been proposed until now.…”