Synthesis, molecular structure and spectroscopic studies of some new quinazolin-4(3H)-one derivatives; an account on the N- versus S-Alkylation

A new series of N- and S-alkylated products of 3-aryl-1H,3H-quinazolin-2,4-dione and 3-aryl-2-mercapto-3H-quinazolin-4-one, respectively, were prepared in good yields via efficient nucleophilic substitution reaction of the SH and NH substrates with methyl iodide, ethyl bromoacetate, allyl bromide, propagyl bromide, 2-bromoethanol, 1,3-dibromopropane or phenacyl bromide in DMF as a solvent and anhydrous potassium carbonate. The quinazolin-2,4-dione favored the N-alkylation while the 2-mercapto-3H-quinazolin-4-one goes via the S-alkylation. DFT reactivity studies showed that the former have the N-site with higher nucleophilicity compared to the O-site. In contrast, the S-site is the more nucleophilic centre than the N-atom of the latter. The structures of the synthesized products have been established on the basis of their melting point (m.p), IR and 1HNMR data. The molecular structures of the products were calculated using the DFT B3LYP/6-311G(d,p) method. The electronic and spectroscopic properties (Uv–Vis and NMR spectra) were calculated using the same level of theory. The chemical reactivity descriptors that could help to understand the biological activity of the products are also predicted. [Display omitted] •A new series of N- and S-alkylated quinazolins derivatives were synthesized.•The 2-mercapto-3H-quinazolin-4-one, 1 goes via the S-alkylation.•The quinazolin-2,4-dione, 12 favored the N-alkylation.•Chemical reactivity and site selectivity of the reactants 1 and 12 were presented.•The molecular structures, electronic and spectroscopic properties of the products were predicted.