Benzodithiophene and benzotrithiophene as π cores for two-and three-blade propeller-shaped ferrocenyl-based conjugated systems

The syntheses of linear and star-shaped bis- and tris(ferrocenyl) derivatives of benzo[1,2-b:4,5-b′]dithiophene and benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene are achieved through one-pot CuI/TMEDA-catalyzed (TMEDA = tetramethylethylenediamine) multiple annulations of bromoethynylbenzenes with sodium sulfide. In addition, the preparation of the parent benzotrithiophene in a good yield with a short reaction time is achieved through the threefold annulation of 1,3,5-trifluoro- Introduction Benzo[b]thiophene (BT, Scheme 1) and its derivatives are an important class of fused thiophene compounds owing to their wide range of biological properties[1,2] and various applications in materials science.[3] Scheme 1. Fused thiophene compounds: benzo[b]thiophene (BT), benzo- [1,2-b:4,5-b′]dithiophene (BDT), and benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene (BTT). In particular, (multi)thiophene fused aromatic compounds are attracting interest as promising electronic materials for organic conductors,[4] organic light-emitting diodes,[5] photovoltaic cells,[6] and field-effect transistors.[7] For this reason, thiophene- based π-conjugated oligomers have been investigated widely as organic semiconductors.[8] Recently, much effort has been focused on benzo[1,2-b:4,5-b′]- dithiophene (BDT) and benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene (BTT, Scheme 1) as potential π cores for a new class of organic semiconductors as they contain two or three identical thiophene moieties with C2h or C3h symmetries that enable twoand three-dimensional molecular extensions. [a] Department of Chemical Sciences, University of Padova Via Marzolo 1, 35131 Padova, Italy E-mail: saverio.santi@unipd.it http://www.chimica.unipd.it/ Supporting information and ORCID(s) from the author(s) for this article are available on the WWW under https://doi.org/10.1002/ejoc.201701045. Eur. J. Org. Chem. 2017, 5966–5974 5966 © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2,4,6-tris(trimethylsilyl)ethynylbenzene. The computed structural and electronic features of these ferrocenyl derivatives as well as their UV/Vis spectra and electrochemistry are discussed, and the results provide insights into the effect of the presence of three rather than two ferrocenyl units. To the best of our knowledge, 2,5,8-tris(ferrocenyl)benzo[1,2-b;3,4-b′;5,6-b′′]trithiophene is the first organometallic complex containing benzotrithiophene.