Reaction of 4H-cyclopenta[2,1-b:3,4-b′]dithiophenes with NBS—a route toward 2H-cyclopenta[2,1-b:3,4-b′]dithiophene-2,6(4H)-diones

In this paper we present a detailed study of the bromination reaction of cyclopentadithiophene (CPDT) derivatives, by means of NBS, giving access to either 2,6-dibromo-4H-cyclopenta[2,1-b:3,4-b′]dithiophenes or 2H-cyclopenta[2,1-b:3,4-b′]dithiophene-2,6(4H)-diones (CPDT-2,6-diones). The CPDT-2,6-diones are fully characterized, including an X-ray single crystal structure of one of the representative materials. A mechanism leading to the formation of the latter, which arise as a new class of compounds within the CPDT family, is proposed and is supported by Gibbs free energy calculations. The influence of the solvent, reaction time, and the number of equivalents of NBS on the selectivity of the reaction is discussed.