Chemistry of Pyrazole-3(5)-Diazonium Salts (Review)*

Zwitterionic Energetic Materials: Synthesis, Structural Diversity and Energetic Properties

Zwitterionic compounds are an emergent class of energetic materials and have gained synthetic interest of many in the recent years. Due to their better packing efficiencies and strong inter/intramolecular electrostatic interactions, they often ensue superior energetic properties than their salt analogues. A systematic review from the perspective of design, synthesis, and physicochemical properties evaluation of the zwitterionic energetic materials is presented. Depending on the parent ring(s) used for the synthesis and the type of moieties bearing positive and negative charges, different classes of energetic materials, such as primary explosives, secondary explosives, heat resistant explosives, oxidizers, etc., may result. The properties of some of the energetic zwitterionic compounds are also compared with analogous energetic salts. This review will encourage readers to explore the possibility of designing new zwitterionic energetic materials.

Structure, Z' = 2 Crystal Packing Features of 3-(2-Chlorobenzylidene)-5-(p-tolyl)furan-2(3H)-one

3-(2-Chlorobenzylidene)-5-(p-tolyl)furan-2(3H)-one (1), C18H13ClO2, crystallizes with Z = 8 and Z' = 2, and the structure at 100 K has orthorhombic (Pna21) symmetry. Each kind of molecule takes part in π-π stacking interactions to form infinite chains parallel to the c axis. We believe that the existence of two forms can be explained by the probable rotation around a single C-C bond. The quantum chemical modeling reveals that these molecules are almost equivalent energetically, and they can be described as the two most stable conformers (rotamers) with a minor rotational barrier of about 0.67 kcal/mol.

C6N10O4: Thermally Stable Nitrogen-Rich Inner Bis(diazonium) Zwitterions

Two nitrogen-rich inner bis(diazonium) salts, the 4,4'-dinitro-5,5'-diazo-2,2'-bisimidazole (2) and the 4,4'-dinitro-5,5'-diazo-3,3'-bispyrazole (4) zwitterions, are described. Compound 2 was synthesized unexpectedly from the nitration of 4,4'-dinitro-5,5'-diamino-1H,1'H-2,2'-bisimidazole (1) in a mixture of trifluoroacetic anhydride and 100% nitric acid. Both 2 and 4 show good thermal stability, especially 2 has a decomposition temperature of 199 °C, which is the highest one in any of the reported hydrogen-free nitrogen-rich diazonium salts.

Computer-aided molecular design of pyrazolotriazines targeting glycogen synthase kinase 3

Numerous studies have highlighted the implications of the glycogen synthase kinase 3 (GSK-3) in several processes associated with Alzheimer's disease (AD). Therefore, GSK-3 has become a crucial therapeutic target for the treatment of this neurodegenerative disorder. Hereby, we report the design and multistep synthesis of ethyl 4-oxo-pyrazolo[4,3-d][1-3]triazine-7-carboxylates and their biological evaluation as GSK-3 inhibitors. Molecular modelling studies allow us to develop this new scaffold optimising the chemical structure. Potential binding mode determination in the enzyme and the analysis of the key features in the catalytic site are also described. Furthermore, the ability of pyrazolotriazinones to cross the blood-brain barrier (BBB) was evaluated by passive diffusion and those who showed great GSK-3 inhibition and permeation to the central nervous system (CNS) showed neuroprotective properties against tau hyperphosphorylation in a cell-based model. These new brain permeable pyrazolotriazinones may be used for key in vivo studies and may be considered as new leads for further optimisation for the treatment of AD.

Reactions of 3H-furan-2-ones and 2H-chromen-2-ones with pyrazole-3(5)-diazonium salts

Derivatives of the new heterocyclic system, 6H-chromeno[4,3-e]pyrazolo[5,1-c][1,2,4]triazin-6-one, were obtained by the reaction of pyrazole-3(5)-diazonium salts with 4-hydroxy-2H-chromen-2-one. Similar reactions with 5-phenyl-3H-furan-2-one followed by intramolecular heterocyclization furnished 6-(4-halophenyl)-7-alkyl-2-phenylfuro[2,3-e]pyrazolo[5,1-c][1,2,4]triazines.