Role of non-conventional hydrogen bonding in controlling regioselectivity for nucleophilic aromatic substitution of 4,6-dinitroisoindoline-1,3-dione with 1,2,3-triazole isomers: a computational studies

The nucleophilic aromatic substitution reactions of 4,6-dinitroisoindoline-1,3-dione with 1,2,3-triazole isomers, i.e., 1H-1,2,3-triazole and 2H-1,2,3-triazole, have been investigated theoretically using DFT/B3LYP calculations employing 6-31G(d,p) basis set in gas phase as well as in solvent phase. The computational studies have supported the formation of transition states via one-step concerted mechanism for the nucleophilic aromatic displacement of nitro groups with 1,2,3-triazoles rather than intermediate formation via two-step addition-elimination mechanism. The amination of 4,6-dinitroisoindoline-1,3-dione with 1,2,3-triazole isomers have revealed regioselectivity of peri-attack despite sterically favorable para-attack. The regioselectivity is attributed to the stabilization of the transition state through intra-molecular hydrogen bond C-H···O=C. This work presents the role of C-H bond as an effective hydrogen bond donor. The molecular interactions through hydrogen bonding have been investigated using AIM method. This work shall result in the synthesis of new regioselective 1,2,3-triazole-derived phthalimide compounds possessing potential biological candidature.