Synthesis and Mechanistic Study of Unsymmetric Dibenzo[d,d′]thieno[2,3-b;4,5-b′]dithiophenes from 1-Haloethynyl-2-halobenzenes

Synthesis of thienoacene semiconducting materials has progressed considerably; however, achieving this through straightforward and efficient methods remains significantly challenging. This study presents a thienannulation initiated by the trisulfur radical anion (S3•-) for synthesizing unsymmetric dibenzo[d,d']thieno[2,3-b;4,5-b']dithiophenes (DBTDTs). Therefore, a facile protocol for the synthesis of DBTDTs from 1-(bromoethynyl)-2-chlorobenzene in the presence of a copper catalyst is provided. Using potassium sulfide as the sulfur source, and only 5 mol % copper catalyst, we obtained the desired products with high yields of up to 82%. The reaction involves many advantages, such as an inexpensive copper catalyst, reaction under air, and high yields. Mechanistic studies demonstrate a unique pathway involving free radicals. Furthermore, synthetic applications demonstrate the scalability to gram-scale synthesis and postsynthetic modifications into sulfones with enhanced photophysical properties.