Formation of naphthodithiophene isomers by flash vacuum pyrolysis of 1,6-di(2-thienyl)- and 1,6-di(3-thienyl)-1,5-hexadien-3-ynes

Abstract To develop a synthetic method of thiophene-based polycyclic aromatic compounds, we investigated the tandem cyclization of 1,6-dithienyl-1,5-hexadien-3-ynes under flash vacuum pyrolysis (FVP) conditions at high temperatures (850 or 1050 °C). As a result, several isomeric naphthodithiophene derivatives were obtained as mixtures, from which a few isomers were isolated. The structural assignments of the products were performed on the basis of combination of the experimental and calculated 1 H NMR chemical shifts of either purified products or mixtures of them. Plausible mechanisms for the formation of the products are proposed.