Synthesis of pi-conjugated systems bearing thiophene and pyrrole heterocycles through palladium catalyzed cross-coupling reactions.

A series of thienylpyrroles and bithienylpyrroles together with their formyl derivatives 5aed were synthesized using commercially or readily available coupling components, through three different palladium catalyzed cross-coupling reactions (Suzuki-Miyaura, Stille and decarboxylative coupling). The synthesis of compounds 5 via the Suzuki-Miyaura reaction produced the title compounds in better yields than the other coupling reactions, while, decarboxylative coupling resulted in the lower yields. UV-visible and 1H NMR studies confirm the existence of significant intramolecular charge transfer (ICT) from the donor pyrrole heterocycle to the acceptor group and a high polarizability of the whole pi-conjugated systems. Together these characteristics indicate their strong potential as versatile precursors for the preparation of push-pull heterocyclic compounds for optical applications.The authors thank the Fundação para a Ciência e Tecnologia (Portugal) and FEDER-COMPETE for financial support through the Centro de Química – Universidade do Minho, Projects PTDC/QUI/66251/2006 (FCOMP-01-0124-FEDER-007429), CQ/UM PEst-C/QUI/UI0686/2013 (FCOMP-01-0124-FEDER-037302) and a PhD grant to M. C. R. Castro (SFRH/BD/78037/2011). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased within the framework of the National Program for Scientific Re-equipment, with funds from FCT