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Pi (π) interactions originating from the N-H bond of amine and ethylene moiety have been explored on the mechanism of aromatic nucleophilic substitution (ArSN) of the nitro group of 4-methylene-5,7-dinitroquinazoline with methylamine in the gas phase and solvent media within DFT framework. The free energy profiles confirmed that the amination should take place at peri-position and calculations support the one-step mechanism through a transition state with no intermediate in the reaction route. Stabilisation of peri-transition state by intramolecular weak interaction akin to hydrogen bonding N-H—CH2 = C leads to the regioselective amination at peri-position of 4-methylene-5,7-dinitroquinazoline. The intramolecular hydrogen bond interactions at N-H—CH2 = C in the peri-transition state are strongly supported by a red shift in N-H stretching vibrations in simulated IR spectra and are confirmed by studying energetics of amination of structural/electronic analogues of 4-methylene-5,7-dinitroquinazoline. The present study established that ethylene plays an important role as an efficient H-bond acceptor in fixing the regioselectivity at peri-position in the amination of 4-methylene-5,7-dinitroquinazoline. This is the first-ever report for the exploration of the role of ethylene moiety as a hydrogen bond acceptor in mediating the regioselectivity of organic reactions. [ABSTRACT FROM AUTHOR]

N-Benzylthiazolidine-2-thione is the key for the synthesis of pharmaceutically important compounds. A novel route for the synthesis of N-benzylthiazolidine-2-thione through of CS2 with N-benzylaziridine in the presence of 1,3-di-tert-butylimidazolium-2-dithocarboxylate ( catalyst I) has been proposed by reliable computations performed within the formalism of density functional theory. The mechanism of the proposed reaction is similar to the of tertiary aziridines and using a recyclable catalyst that is reported to provide access to 3-substituted 2-oxazolidones with excellent yield. Because the rate determining step needs to surmount a high energy barrier, the reaction route has been deciphered in high boiling solvent (1, 2-ethanediol). The highlight of the mechanistic route detailed here is that the proposed pathway is a cyclic process that is exothermic in nature with the regeneration of the catalyst and involves simple reagents. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]