Synthesis of New Tetrazole Derivatives of Spiro- and Bis-barbiturates

This work described the synthesis of the first and unprecedented examples of 5-aryl-1H-tetrazoles including spiro- and bis-(thio) barbiturates, generated from the reaction between 4-(1H-tetrazol-5-yl) benzaldehyde with (thio) barbituric acids and cyanogen bromide (BrCN) in the presence of triethylamine, providing good overall yields. Tetrazoles based on bis-(thio) barbiturates were also obtained in the absence of BrCN under the same conditions. The structures were characterized by IR, H-1 NMR, C-13 NMR, X-ray crystallography and mass analysis techniques. The reaction mechanism was proposed. The hydrogen bond strength (E-HB) versus d (O1 center dot center dot center dot center dot center dot O7 (w)) distance (kcal.mol(-1)) and corresponding pKa value for the proton of H-3A (in water molecule) in 4b.H2O were estimated to be 13.8 kcal.mol(-1) and 8.2, respectively.