Superbases DBU, DBN, TMG and MTBD are efficient catalysts which have been used in the solvent free conversion of carbon dioxide and 2-aminobenzonitrile to quinazoline-2,4(1H, 3H)-diones. For the final product, four tautomeric forms have been considered witch the stability of the preferred tautomer has been studied by NBO analysis. In this research two different mechanisms have been proposed for the catalytic behavior of the superbases which can act as a base or a nucleophile in the reaction. Theoretical studies show that two primary steps are the rate determining step (RDS) of the mechanism. QTAIM analysis and local nucleophilicity index were used for investigation of the molecular aspects of the RDSs. Finally, it has been confirmed the basic role of the applied superbases is more important than nucleophilicity and DBU is the best candidate as an efficient catalyst for this reaction.

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