Electrochemical Formation of Carbon-Heteroatom Bond for the Synthesis of Organic Functional Molecules

In recent years, electrochemical organic synthesis has attracted attention and has been re-evaluated as a powerful methodology in synthetic chemistry. Electrochemical organic reactions are classified into direct electrolysis, in which the substrate is directly oxidized or reduced at the electrodes, and indirect electrolysis, in which the substrate is oxidized or reduced by an active species, which is called “mediator”, generated by oxidation or reduction at the electrode. In indirect electrolysis, the reaction between the electrode and the mediator is direct electron transfer, but the reaction between the mediator and the substrate is a “chemical” reaction between the activated mediator and the substrate. Therefore, the use of the appropriate mediator enables uncommon molecular transformations that are usually difficult with high chemoselectivity. We describe here our developed electrochemical carbon-heteroatom bond formations for the synthesis of organic functional molecules with or without mediators. Electrochemical dehydrogenative C-S bond formation proceeded to afford thienoacenes. The use of Br− as a mediator was essential for the reaction. This methodology could also be applicable for the synthesis of dibenzothiophene derivatives. We also developed electrochemical C-P bond formation for the synthesis of dibenzophosphole oxides (DPOs) using DABCO as a mediator. Sultones, sulfur analogs of lactones, could be synthesized by electrochemical C-O bond formation of sulfonates. The reaction is direct electrolysis which proceeds via radical pathway. We also found that direct electrolysis of biaryl sulfonyl hydrazides afforded dibenzothiophene dioxides via electrochemical C-S bond formation.