The photochemistry of 1-methyl-4-phenyl-1H-tetrazole-5(4H)-thione (1a) and 1-(3-methoxyphenyl)-4-methyl-1H-tetrazole-5(4H)-thione (1b) was studied in acetonitrile at 254 and 300 nm, which involves expulsion of dinitrogen and sulfur to form the respective carbodiimides 5a,b as sole photoproducts. Photolysis of the title compounds in the presence of 1,4-cyclohexadiene trap led to the formation of respective thioureas, providing strong evidence for the intermediacy of a 1,3-biradical formed by the loss of dinitrogen. In contrast, a trapping experiment with cyclohexene provided no evidence to support an alternative pathway of photodecomposition involving initial desulfurization followed by loss of dinitrogen via the intermediacy of a carbene. Triplet sensitization and triplet quenching studies argue against the involvement of a triplet excited state. While the quantum yields for the formation of the carbodiimides 5a,b were modest and showed little change on going from a C6H5 (1a) to mOMeC6H4 (1b) substituent on the tetrazolethione ring, the highly clean photodecomposition of these compounds to a photostable end product makes them promising lead structures for industrial, agricultural, and medicinal applications.

A series of 1,4-diaryl tetrazol-5-ones were synthesized by copper mediated N-arylation of 1-phenyl-1H-tetrazol-5(4H)-one with aryl boronic acids, o-R1C6H4B(OH)2 where R1 = H, OMe, Cl, CF3, Br, CCH. The 1,4-diaryl tetrazol-5-ones substituted with OMe, Cl, CF3, Br underwent thionation with Lawesson’s reagent to yield the corresponding 5-thio derivatives. The 1-(2-bromophenyl)-4-phenyl-1H-tetrazole-5(4H)-thione so obtained was subjected to lithiation/protonation and Sonogashira coupling to produce 1,4-diphenyl-1H-tetrazole-5(4H)-thione and 1-(2-ethynylphenyl)-4-phenyl tetrazole-5-thione, respectively. The title compounds were found to be stable to strong Lewis acid conditions. Three of these novel compounds were found to inhibit L1210 leukemia cell proliferation and SK-BR-3 breast cancer cell growth over several days in culture in vitro. Shorter tetrazole derivative treatments also reduced the expression of the Ki-67 marker of cell proliferation in SK-BR-3 cells and the rate of DNA synthesis in L1210 cells.We report the synthesis of a series of 1,4-diaryl tetrazol-5-ones and tetrazole-5-thiones that inhibit the proliferation of L1210 and SK-BR-3 tumor cells in vitro.

This manuscript reports crystallographic data on 1-(3-methoxyphenyl)-1H-tetrazol-5(4H)-one (2a), 1-(4-methoxyphenyl)-1H-tetrazol-5(4H)-one (2b), 1-(3-methoxyphenyl)-4-methyl-1H-tetrazol-5(4H)-one (3a) and 1-(4-methoxyphenyl)-4-methyl-1H-tetrazol-5(4H)-one (3b). 2a and 2b associate in the solid-state to form dimers through the formation of hydrogen bonds. There are no strong structure-directing interactions present in the crystal lattices of 3a and 3b, and packing in these molecules is attributed to weak electrostatic interactions of the type N⋯H–C and C–H⋯π. The analyses of the structural parameters show that there is some degree of electron delocalization in the heterocyclic ring.

The syntheses of 1-(4-methoxyphenyl)-4-methyl-1H-tetrazol-5(4H)-thione 1a, 1-methyl-4-phenyl-1H-tetrazole-5(4H)-thione 1b, 1-(4-chlorophenyl)-4-methyl-1H-tetrazol-5(4H)-thione 1c, 1-methyl-4-(4-nitrophenyl)-1H-tetrazol-5(4H)-thione 1d were carried out and their electronic absorption spectra were obtained in cyclohexane, THF, and acetonitrile. The UV spectra of 1a–d showed a modest dependence on the polarity of the solvent. The change of substituent on the tetrazolethione ring from a strongly electron donating group (p-C6H4OMe, 1a), to a moderately electron donating (C6H5, 1b) to a weakly electron withdrawing group (p-C6H4Cl, 1c) also produced minimal effect on the electronic properties of 1a–c. However, the presence of a strongly electron withdrawing group (p-C6H4NO2, 1d) on the heterocyclic ring produced a marked change in the UV spectrum. Time-dependent density functional calculations revealed that all the bands result from π → π* excitations with some degree of intramolecular charge transfer (ICT) within the molecules. Our studies further showed that as the acceptor strength is increased in the order: 1a (p-C6H4OMe) < 1b (C6H5) < 1c (p-C6H4Cl) < 1d (p-C6H4NO2), the ICT also increases. In accordance with the experimental observations, the calculated transitions also showed modest dependence on the polarity of the solvent.