Against the background, we turned our attention to the electrochemical synthesis of BTBT derivatives by sequential double C-S coupling in one-pot. In our preliminary study, we assumed that S-Me-protected bis(o-sulfanylphenyl)acetylene could be used as a substrate for the sequential electro-oxidative cyclization, but bromocyclization predominantly proceeded and the desired product was not obtained (Scheme 1D). After several examinations, we finally found that a methoxymethyl (MOM) group, which is not a common protecting group for S atoms, is an efficient protecting group for halogen-mediated electrochemical C-S bond formation. We herein report a synthesis of thienoacenes from S-MOM-protected bis(osulfanylphenyl)acetylene derivatives via electrochemical doublecyclization using a halogen mediator (Scheme 1E). To the best of our knowledge, this is the first application of a MOM group to electrochemical C-S bond formation.