Electrocatalytic synthesis of α,α--dihalide ketones from α-mono-halide ketones and unexpected dimer condensation

• Published in: Green chemistry : an international journal and green chemistry resource : GC Vol. 24; no. 7; pp. 2859 - 287
• Main Authors: Zhou, Bei, He, Yu-Juan, Tao, Yun-Feng, Liu, Lan-Xiang, Hu, Min, Chang, Zu-Hui, Lei, Hong, Lin, Jun, Lin, Tong, Du, Guan-Ben
• Format: Journal Article
• Published: 04.04.2022
• DOI: 10.1039/d1gc04584a
• ISSN: 1463-9262

A novel, environmentally friendly electrocatalytic process has been developed to prepare α,α- gem -dihalide (F, Cl, and Br) ketones from α-mono-halide ketones in an aqueous solution containing alkali halide salts. The gem -dihalides could have the same or different halogens on the same carbon, depending on the reactant and inorganic halide salt used. An electron-withdrawing group, such as carbonyl, located at the α-site of mono-halogenated carbon, was essential to the reaction. The electrosyntheses were performed under ambient conditions without inert gas protection and displayed yields of about 80%. This method avoided the classical haloform elimination reaction. However, when the aqueous solution contained NaOH, two α-mono-halide ketone molecules had a special dimer condensation. The reaction mechanisms were explored by conducting GC-MS, EPR, and CV with DFT calculations. These revealed that in situ generation of a halogen radical initiated electrocatalytic halogenation, while the dimer condensation involved a hydroxyl radical-mediated C1 fragment elimination. Starting from α-mono-halide ketone, this paper demonstrates a novel electrocatalytic method of halogenation for α,α- gem -dihalide ketone synthesis and a NaOH-mediated dimer condensation reaction for keto-ester synthesis.