Thienoacenes, sulfur-containing π-conjugated molecules, have been widely used as active compounds for organic materials such as organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). In particular, thienoacenes bearing thieno [3,2-b]thiophene (TT) moieties, such as [1]benzothieno [3,2-b][1]benzothiophene (BTBT), dinaphtho [2,3-b:2',3'-f]thieno [3,2-b]thiophene (DNTT), and dibenzo [d,d']thieno [3,2-b;4,5-b']dithiophene (DBTDT), exhibit excellent OFET properties (Figure ). While there have been many reports on the synthesis of thienoacenes, one of the most efficient and attractive ways to synthesize thienoacenes is the formation of multiple C-S bonds in a single step. Because unprotected S-H bonds are easily oxidized to S-S bonds, protection of the S atom is often required, especially when compounds with two thiol moieties are used as starting materials. Methyl protection has been widely used for this purpose. For instance, Takimiya reported that bis(naphthalenyl)ethene bearing two methylsulfanyl groups reacted with an excess amount of iodine to afford a highly π-expanded thienoacene such as DNTT (Scheme 1A). While this strategy is efficient for constructing a BTBT skeleton, an excess amount of iodine was required and only highly π-extended substrates could be used. Recently, Kitamura and co-workers reported an I2/PhI(OAc)2-mediated cyclization of diphenylacetylenes bearing methylsulfanyl groups (Scheme 1B). An iodocyclized product was obtained and subsequent photocyclization was required to synthesize the desired BTBT derivatives. One-step construction of multiple C-S bonds is still challenging and it should be a powerful tool for constructing thienoacenes efficiently. Meanwhile, electrochemical carbon-heteroatom bond formation is an environmentally benign method that proceeds under mild conditions and is a powerful tool for organic synthesis. Among these reactions, electrochemical C-S bond formation has recently received considerable attention (Scheme 1). For instance, Lei et al. reported anodic C-S bond formation between electron-rich arenes and arylthiols. Wirth and Xu reported the electrochemical intramolecular coupling of thiocarbonyl compounds for the synthesis of benzothiazoles. We have been interested in the electrochemical synthesis of πconjugated compounds and recently reported dehydrogenative C-S coupling for the synthesis of thienoacenes and dibenzothiophenes using a halogen mediator (Scheme 1C).