Synthesis and Applications of Benzothienobenzofurans: A Review

Heteroacenes are considered as an important class of compounds for material applications due to their stability, electron‐richness and tunable properties. Mostly, four ring containing heteroacenes have found immense applications in organic electronic devices and some of them have been successfully commercialized. One such class of heteroacene are benzothienobenzofuran for which four different isomers are reported to date based on the position where the benzothiophene unit is fused to the benzofuran ring. The available literature claims different synthetic strategies towards the benzothienobenzofurans starting from multistep synthesis to tandem transformations, electrochemical synthesis and annulations. Different metal catalyzed transformations including Pd‐catalyzed dual C‐H activations, Ullmann coupling, dual metal‐catalyzed one‐pot processes etc. are reported for the synthesis of different isomers of benzothienobenzofurans. The present review analyses all the synthetic methodologies reported for the preparation of the four isomers and examines the generality of each method by highlighting its advantages and disadvantages. We discuss all available mechanisms of the reactions for the benefit of the readers. Finally, the existing basic photophysical properties of benzothienobenzofurans and their limited applications in fabricating devices for organic light‐emitting diode (OLED), organic field‐effect transistor (OFET), and organic phototransistor (OPT) uses are deliberated