4-Phenyl-1,2,4-triazole-3,5-dione as a novel and reusable reagent for the aromatization of 1,4-dihydropyridines under mild conditions

Synthesis of trifold-labeled versatile reagent [3,5-13 C2 ,4-15 N]4-phenyl-1,2,4-triazoline-3,5-dione

Triazolinediones are an important class of derivatization agents that have found application in various research disciplines. Their unique reactivity often allows precise and selective tagging of relevant molecular scaffolds to facilitate structural elucidation, tracking in biological systems, and stabilization of labile compounds. Recent research efforts mainly focused on the development of novel fluorescent and ionizable or isotopically labeled tags improving the quantification and identification of the parent molecule by suitable analytical methods. However, these concepts often lack the ability to improve properties facilitating the analysis by nuclear magnetic resonance (NMR) spectroscopy. We herein describe the first synthesis of 13 C and 15 N labeled [3,5-13 C2 ,4-15  N]4-phenyl-1,2,4-triazoline-3,5-dione utilizing the Cookson/Zinner-Deucker synthesis of urazoles. The introduced isotopic labels are ideally suited to support the structural elucidation of unknown and complex derivatization mixtures by NMR, thereby exploiting the increased sensitivity of detecting long-range JHC and additional JCC and JCN couplings within the derivatized compounds of interest.

Tetramethylguanidine-functionalized melamine as a multifunctional organocatalyst for the expeditious synthesis of 1,2,4-triazoloquinazolinones

Novel nano-ordered 1,1,3,3-tetramethylguanidine-functionalized melamine (Melamine@TMG) organocatalyst was prepared and adequately identified by various techniques including FTIR, EDX, XRD and SEM spectroscopic or microscopic methods as well as TGA and DTG analytical methods. The Melamine@TMG, as an effective multifunctional organocatalyst, was found to promote smoothly the three-component synthesis of 1,2,4-triazoloquinazolinone derivatives using cyclic dimedone, 3-amino-1,2,4-triazole and different benzaldehyde derivatives in EtOH at 40 °C. This practical method afforded the desired products in high to excellent yields (86-99%) and short reaction times (10-25 min). The main advantages of this new method are the use of heterogeneous multifunctional nanocatalyst, simple work-up procedure with no need for chromatographic purification, highly selective conversion of substrates and recyclability of the catalyst, which could be used in five consecutive runs with only a small decrease in its activity.

The first computational study for the oxidative aromatization of pyrazolines and 1,4-dihydropyridines using 1,2,4-triazolinediones: an anomeric-based oxidation

The oxidative aromatization of 1,3,5-trisubstituted pyrazolines and 1,4-dihydropyridines using 1,2,4-triazolinediones as oxidizing agents was studied. It is confirmed that the “anomeric-based oxidation” passes through a concerted oxidation via hydrogen abstraction–addition.

Studies on tautomerism in the triazoline dione

The chemical properties of the triazoline dione have been extensively studied. The relative stability of three tautomers in the gas phase and solution (using PCM model) are evaluated using HF and DFT methods and compared with MP2 level using different basis sets. The results of the calculations indicate that 4H-1,2,4-triazole-3,5-dione (K form) is more stable in the gas phase than in solution. In addition, the transition states of proton transfer reaction is calculated. The vibrational frequencies and corresponding normal mode assignments of 4H-1,2,4-triazole-3,5-dione and 5-hydroxy-3H-1,2,4-triazol-3-one (E1 form) are also theoretically examined. In addition, the variation of dipole moments and charges on atoms with change of solvent is studied. Specific solvent effects with addition of one molecule of water near the electrophilic centers of three tautomers and the transition state of proton transfer assisted by a water molecule was investigated. Aggregation with water molecules does not change the order of stability of isomers, but proton transfer reaction assisted by a water molecule needs less energy than the intramolecular process.

A convenient and efficient protocol for oxidative aromatization of Hantzsch 1,4-dihydropyridines using benzyltriphenylphosphonium peroxymonosulfate under almost neutral reaction conditions

Oxidative aromatization of 4-alkyl or aryl and heterocyclic-substituted derivatives of Hantzsch 1,4-dihydropyridines to the corresponding pyridine derivatives has been studied using benzyltriphenylphosphonium peroxymonosulfate as an oxidant in the presence of BiCl(3) under nearly neutral reaction conditions at ambient temperature.