EFFECT OF LEWIS ACID CATALYSTS ON THE POSITIONAL SELECTIVITY OF THE ELECTROPHILIC AROMATIC SUBSTITUTION ON α-SUBSTITUTED THIOPHENES: A CONCEPTUAL DFT INVESTIGATION

The α′/β regioselectivity of the electrophilic aromatic substitution of some thiophene α-substituted derivatives (R = CHO, COMe or CO2Me), catalyzed and not catalyzed by the Lewis acid, AlCl3, has been investigated by means of the local nucleophilicity index, recently proposed by Perez et al. [J Mol Struct: Theochem895: 86, 2009]. The quantum chemistry calculations, carried out at the B3LYP/6-311G(d,p) level of theory, show that the α′-substitution is preferred in absence of the catalyst, while the β-substitution is more favored in the presence of the catalyst. The theoretical results, predicted using DFT-based reactivity indices, are in good agreement with the experimental outcomes.