Modular Synthesis of [1]Benzothieno[3,2-b][1]benzothiophenes via Formation of C–S and C=C Bonds

We report a new method for the synthesis of valuable [1]benzothieno[3,2-<i>b</i>][1]benzothiophenes (BTBTs) using inexpensive and readily available <i>ortho</i>-halobenzyl halides as starting materials. This protocol is catalyst-free, features moderate to good yields, and exhibits efficient formation of four C-S bonds and one C=C bond in a domino reaction. Notably, unsymmetric BTBTs were also synthesized in good yields using bis(2-halophenyl)acetylene and bis(2-halophenyl)ethylene as starting materials, providing an efficient pathway for the construction of unsymmetric BTBTs. Mechanism studies have demonstrated a pathway involving the trisulfur radical anion (S₃^•-).