Base-promoted ring expansion of 3-aminopyrimidine-2-thiones into 1,2,4-triazepine-3-thiones

Nickel(II) complexes with 14-membered bis-thiosemicarbazide and bis-isothiosemicarbazide ligands: synthesis, characterization and catalysis of oxygen evolution reaction

Design and development of novel, low-cost and efficient electrocatalysts for oxygen evolution reaction (OER) in alkaline media is crucial for lowering the reaction overpotential and thus decreasing the energy input during the water electrolysis process. Herein, we present the synthesis of new 14-membered bis-thiosemicarbazide and bis-isothiosemicarbazide macrocycles and their nickel(II) complexes characterized by spectroscopic techniques (1H and 13C NMR, IR, UV-vis), electrospray ionization mass spectrometry, single crystal X-ray diffraction, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) and cyclic voltammetry. Finally, the activity of nickel(II) complexes towards OER is reported. NiIILSEt delivered a current density of 10 mA cm-2 at the lowest overpotential of 350 mV with the lowest Tafel slope of 93 mV dec-1. The high performance of NiIILSEt might be attributed to its high surface area and thus abundant active sites with the observed low charge-transfer resistance enabling the effective current flow through the electrocatalyst. Square-planar coordination geometry and increment in Ni oxidation state are believed to favor its OER performance. Beside high activity towards OER, NiIILSEt demonstrated excellent long-term stability with continuous operation, advocating its possible application in commercial systems.

Different Modes of Acid-Promoted Cyclooligomerization of 4-(4-Thiosemicarbazido)butan-2-one Hydrazone: 14-Membered versus 28-Membered Polyazamacrocycle Formation

Unprecedented self-assembly of a novel 14-membered cyclic bis-thiosemicarbazone or/and a 28-membered cyclic tetrakis-thiosemicarbazone upon acid-promoted cyclooligomerization of 4-(4-thiosemicarbazido)butan-2-one hydrazone has been discovered. A thorough study of the influence of various factors on the direction of macrocyclization provided the optimal conditions for the highly selective formation of each of the macrocycles in excellent yields. Plausible pathways for macrocyclizations have been discussed. The macrocycle precursor was prepared by the reaction of readily available 4-isothiocyanatobutan-2-one with an excess of hydrazine.

New Reaction Products of Acetylacetone with Semicarbazide Derivatives

A new approach is suggested herein for the synthesis of pyrazole derivatives by reacting 4-nitrosemicarbazide with acetylacetone. Additional studies were done on the reaction of acetylacetone with semicarbazide and its derivatives (4-aminosemicarbazide, methylsemicarbazide, and dimethylsemicarbazide). The study on the reaction with acetylacetone resulted in monocyclic 3,5-dimethyl-N-nitropyrazole-1-carboxamide, monocyclic 5-hydroxy-3,5-dimethyl-2-pyrazoline, and bicyclic bis(3,5-dimethylpyrazole-1-carbonyl)hydrazine, and conditions for the formation of acetone semicarbazone were identified. The structures of the resultant compounds were validated by physicochemical analytical methods, including X-ray diffraction. The computer-aided screening in the PASS prediction software discovered a high biological activity of the newly obtained compounds.

A convenient stereoselective access to novel 1,2,4-triazepan-3-ones/thiones via reduction or reductive alkylation of 7-membered cyclic semicarbazones and thiosemicarbazones

Stereoselective syntheses of 1-unsubstituted and 1-alkylsubstituted 1,2,4-triazepane-3-thiones/ones based on reduction or reductive alkylation of 2,4,5,6-tetrahydro-3H-1,2,4-triazepine-3-thiones/ones are reported.