Regioselectivity study of 1,3-dipolar cycloaddition of 2-azido-N-(4-diazenylphenyl)acetamide with terminal alkyne through DFT analysis

Abstract

The mechanism and regioselectivity of 1,3-dipolar reaction of 2-azido-N-(4-diazenylphenyl) acetamide and an alkyne have been studied in gas phase and in DMSO using the B3LYP-GD3 functional and 6-31G(d,p) basis set. The reaction followed a one-step mechanism with asynchronous TSs. The calculated global reactivity indices calculated revealed, among other things, the nucleophile character of the 2-azido-N-(4-diazenylphenyl)acetamide and the electrophile character of the alkyne (4-bromo-2-chloro-1-ethynylbenzene), in addition to an electron transfer from the 4-bromo-2-chloro-1-ethynylbenzene towards the 2-azido-N-(4-diazenylphenyl) acetamide. The calculated local reactivity indices predicted the formation of the 1,4-triazole, with the most nucleophilic nitrogen and the most electrophilic carbon favoring its formation. However, analysis of the activation energies and thermochemistry parameters showed that the 1,5 triazole is energetically favorable and more stable under thermodynamic control. Bond order analysis coupled with bond formation evolution and the solvent effect was further investigated to support and highlight the asynchronicity in bond formation and the regioselectivity of the reaction, respectively.