DFT study of the condensation products of 2-chloro-3-formylquinolines with o-aminophenol, o-aminothiophenol and o-phenylenediamine

The reaction mechanism for the synthesis of quinoline-fused benzo/dia/oxa/thia/zepins is investigated using the DFT/B3LYP/6-31G(d) method. DFT conceptual reactivity indices analysis allows classification of o-aminophenol (2, X = O), o-aminothiophenol (2, X = S) and o-phenylenediamine (2, X = N) and R-substituted 2-chloroquinoline-3-carbaldehydes (1 ac) as strong electrophiles, suggesting a polar process. Besides, Parr functions and Fukui indices predict the most reactive sites for observed experimentally product formation, in agreement with the dual descriptor analysis. In the energy aspect, there is no effect of the R (R = CH3, OCH3) substituent on the thermodynamic quantities, whereas the substitution of the X has a remarkable effect. The products (4a–c, X = N) are the most stable, and their cyclizations are the easiest. An extended analysis was performed using the activation strain model/energy decomposition analysis ASM/EDA model. The obtained results indicate that the orbital interaction and electrostatic stabilizations are the principal factors favoring the reaction with X = N. Topological analysis of the electron localization function (ELF) of the bending point structures along the reaction path indicates that the reaction occurs via a non-concerted two-step mechanism.