Chiral bis(benzo[1,2-b:4,3-b’]dithiophene)s: synthesis and stereochemical characterization

Thiophene-containing fused aromatic compounds are an interesting class of -conjugated systems in functional organic materials (1). Among them, benzo[1,2-b:4,3-b’]dithiophene (BDT) and its derivatives are widely studied, for instance as units in mono and polydisperse oligomers in the field of the materials science (2), and as -spacers in push-pull organic chromophores for photovoltaic applications (3). Furthermore, BDT is a key intermediate for the synthesis of inherently chiral helical systems such as tetrathia[7]helicenes (4).Thus, BDT can be identified as a key starting molecule, which can allow access to more complex and interesting systems through a judicious functionalization of the -positions of the thiophene rings. In our ongoing studies on the synthesis and functionalization of BDTs (5,6), we have developed a novel synthesis to prepare bis(benzo[1,2-b:4,3-b’]dithiophene) systems 2, starting from bromides 1 (Figure 1).Compounds 2 belong to an interesting class of chiral atropisomeric heterobiaryl derivatives with C2-symmetry, which can be selectively functionalized into bromides 3. The chiroptical properties of both systems 2 and 3 have been fully elucidated by experimental and theoretical studies. On the other hand, enantiopure bromides 3 represent useful intermediates for the enantioselective synthesis of the corresponding tetrathiahelicene derivatives.