Abstract Cyclohepta [cd] benzothiophene 3, a new heterocyle, was synthesized starting from benzothiophene via eight steps in 14% total yield. Chemical reactions of 3 were examined on formylation, acetylation, bromination, catalytic hydrogenation and Diels-Alder reactions. The results show that the benzothiophene moiety of 3 has aromatic character and the carbon [DOUBLE BOND] carbon double bonds in a seven-membered ring posseses ...