Synthesis of benzodithiophene systems by a ligand-free Suzuki-Miyaura coupling reaction in Deep Eutectic Solvents

Abstract

Benzo[1,2-b:4,3-b\u2019]dithiophene (BDT) and its derivatives belong to an interesting class of thiophene-based aromatic \u3c0-conjugated compounds that are widely studied as functional organic materials inserted, for instance, as units in mono and polydisperse oligomers, or as \u3c0-spacers in push-pull organic chromophores for photovoltaic applications1. Moreover, BDTs are key intermediates for the synthesis of inherent chiral tetrathia[7]helicenes, which are an attractive class of heterohelicenes with unique physicochemical and chiroptical properties due to their helix-like structure2. Thus, BDT is a key starting molecule which can allow access to more complex and interesting systems through a selective and judicious functionalization of the \u3b1 and \u3b2-positions of the terminal thiophene rings. Building on our recent studies on the synthesis and functionalization of BDTs3, we questioned whether a novel class of 2,7-diarylsubstituted BDTs 1 (Figure 1) could be synthesized via a palladium-catalysed Suzuki-Miyaura reaction between heteroaryl halides 2 and organoboron derivatives 3 in Deep Eutectic Solvents (DESs), which have proven to be effective as sustainable and environmentally responsible reaction media in several transition-metal-catalyzed reactions4. In this communication, we report our preliminary results on the preparation of diarylsubstituted BDTs 1, and discuss the substrate scope of the proposed protocol. Some of the compounds so far obtained display interesting photophysical properties, which are currently under investigation