“One-Pot” Reaction Involving Ring Formation of Silole, Thiophene Ring-Opening Alkynylation, and S−S Coupling

With 4,4′-dibromo-2,2′,5,5′-tetrakis(trimethylsilyl)[3,3′]bithienyl (4) as substrate in the presence of t-BuLi (4 equiv)/CuCl2, a compound with a novel structure, a D2-symmetric derivative of thienosilole (1), is prepared in 55−64% yield. Three steps of bond breaking and bond forming are involved in the “one-pot” reaction to form 1: (1) a C−Si bond forms in the ring formation of silole; (2) a C−S bond breaks in thiophene ring-opening alkynylation; (3) a S−S bond forms in the CuCl2-promoted coupling. On the other hand, if a short time for Br/Li exchange was used in the process, the intramolecular coupling compound tetrakis(trimethylsilyl)cyclobuta[1,2-c:3,4-c′]dithiophene (2) was obtained instead. 2 could be obtained in 11−20% yield. None of the intermolecular coupling compound octakis(trimethylsilyl)tetrathienylene (5) was observed.