New syntheses of tricyclic thiophenes and cyclic tetrathiophenes using transition-metal-catalyzed cyclization

New synthetic methods for polycyclic thiophenes were developed. Thus, dithi enothiophenes, cyclopentadithiophene, silacyclopentadithiophenes, and cyclo octatetrathiophenes were synthesized in moderate to good yields by using th e CuCl2-mediated cyclization of organocopper(I) and organozinc intermediate s prepared from dilithio-derivatives with CuCN or ZnCl2, respectively. A di rect cyclization of bromothiophene derivatives with hexamethylditin in the presence of tetrakis(triphenylphosphine)palladium(0) also gave dithienothio phenes, cyclopenta-dithiophenes, and silacyclopentadithiophenes in good yie lds.