Non-photochemical Synthesis of Functionalized Benzo[1,2-b:4,3-b’]dithiophene Derivatives

Thiophene-containing fused, aromatic compounds represent an interesting class of π-conjugated systems in functional organic materials. A role of increasing importance is going to be acquired by benzo[1,2-b:4,3-b’]dithiophene (BDT) which have been studied as units in mono and polydisperse oligomers in field of the materials science, and, more recently, as π-spacers in push-pull organic chromophores for photovoltaic applications1. Moreover, BDT represents a key intermediate in the synthesis of inherently chiral helical systems such as tetrathia[7]helicenes2. Within this context, and in view of potential wider and industrial applications, simple, reliable, reproducible and economic syntheses of BDTs, which avoid the use of photochemical pathway are highly desirable. Herein, we report the first results of our investigations on the FeCl3-mediated cyclization of αα’-disubstituted Z-alkenes 1 as a general and non-photochemical synthesis of BDT derivatives 2.3 The influence of the temperature and the nature of the substituents, in determining the scope and limitations of this methodology have been also explored.