A Sequential Annulation Strategy for the Regiocontrolled Construction of Structurally Defined Ladder-Type Oligothiophenes

We developed a concise synthetic method for the regiocontrolled annulation of a fused thiophene ring onto a preexisting thiophene framework. The sequence involves halogenation, a halogen-dance reaction, Sonogashira coupling, and diisobutylaluminum hydride-promoted C-S bond-forming cyclization, enabling access to regioisomeric ladder-type oligothiophenes that cannot be accessed by conventional approaches. This strategy provides an effective approach for the regioselective construction of sulfur-embedded ladder systems with well-defined fused ring patterns.