Electrophilic Substitution Reactions of Thiophene and Thieno[2,3-B]thiophene Heterocycles: a DFT Study

Abstract We determined the most preferred site for the electrophilic aromatic substitution (SEAr) reactions of thiophene 1 and thieno[2,3-b]thiophene 2 using the N-chlorosuccinimide electrophile in the gas phase and in acetic acid. The B3LYP/6-311G(d), B3LYP-D3/6-311G(d) and M06-2X/6-311G(d) methods were employed to investigate the SEAr reaction mechanisms. We found that, compared to the β-carbon atom, the α-carbon atom in both 1 and 2 is preferred for electrophilic attack both kinetically and thermodynamically.