In this paper the mechanism of the benzoannelated thieno[3,2-b]furan halogenation reaction has been characterized using density functional theory calculations. The solvent effect on the studied reaction is taken into account. A variation in charge, bond length, and bond order in the transformation of the π-complex to the σ-complex and final products along the reaction minimal energy path given as the intrinsic reaction coordinate has been investigated. Particular attention was focused on the evolution of π MOs along the reaction coordinate. The importance of HOMO-HOMO interaction between the lone pair electrons of the bromine molecule and π MOs of thieno[3,2-b]benzofuran has been emphasized.