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An efficient synthesis of novel triazoles incorporating barbituric motifs via [3+2] cycloaddition reaction: An experimental and theoretical study

Darroudi Mahdieh (University of Mazandaran, Faculty of Chemistry, Department of Organic Chemistry, Babolsar, Iran)
Sarrafi Yaghoub (University of Mazandaran, Faculty of Chemistry, Department of Organic Chemistry, Babolsar, Iran)
Hamzehloueian Mahshid (Islamic Azad University, Jouybar Branch, Department of Chemistry, Jouybar, Iran)

In this work, the synthesis of novel triazole derivatives with barbituric motifs in good yields is described. The alkyne was prepared through the Knoevenagel reaction of barbituric derivatives with ortho and para O-propargylated hydroxybenzaldehyde. The mechanism and regioselectivity of this [3+2] cycloaddition reaction were investigated using the density functional theory at the B3LYP/6-31+G(d) level of theory. The computational studies revealed that a di-copper catalyzed stepwise mechanism, involving six-membered ring intermediate, is the preferred pathway. The regioselectivity was explained in terms of frontier molecular orbital (FMO) interactions, local and global electrophilicity and nucleophilicity indices. Accordingly, the favored interactions for di-copper acetylide are in good agreement with the observed regioselectivity, while completely opposite results were obtained for a possible uncatalysed reaction.

Keywords: triazoles, barbituric derivatives, DFT study, mechanism