Cyclic Hybrids of Alternately Linked 2,5-Pyrrolylenes and 3,4-Thienylenes

Cyclic hybrids consisting of alternately linked 2,5-pyrrolylene and 3,4-thienylene units were synthesized by Suzuki–Miyaura cross-coupling reaction of 3,4-diborylthiophene with 3,4-bis(5-bromopyrrol-2-yl)thiophene with the RuPhos-PdCl precatalyst in low yields. The same coupling reaction with Boc-protected 3,4-bis(5-bromopyrrol-2-yl)thiophene afforded a tetrameric cyclic hybrid selectively in 11% yield. Conjugative electronic interactions in these cyclic hybrids are weak, plausibly owing to the cross-conjugation nature of the 3,4-thienylene units.