Electrochemical cycloaddition of hydrazones with cyanamide for the synthesis of substituted 5-amine-1,2,4-triazoles

An eco-friendly and efficient electrochemical method for the synthesis of 5-amine-1,2,4-triazole derivatives has been developed by employing hydrazones or in situ generation of hydrazones with cyanamide using KI as the catalyst and electrolyte. This strategy could be smoothly conducted with simple reaction conditions at room temperature without the addition of a chemical oxidant in an undivided cell, and cyanamide has been proven to be of great value in electrosynthesis.

Environmentally Benign and User-Friendly In Situ Generation of Nitrile Imines from Hydrazones for 1,3-Dipolar Cycloaddition

Nitrile imines are highly reactive and versatile dipoles and conventionally generated in situ from unstable hydrazonyl halides under basic conditions. Herein, we report the first green and user-friendly protocol for in situ generation of nitrile imines from Oxone-KBr oxidation of hydrazones and base-promoted dehydrobromination. The nitrile imines were demonstrated for 1,3-dipolar cycloaddition with various dipolarophiles, including alkene and alkyne groups. With its green nature, ease of operation, and air and moisture tolerance, we expect our method will find wide applications in organic synthesis.

Selective Buchwald–Hartwig arylation of C-amino-1,2,4-triazoles and other coordinating aminoheterocycles enabled by bulky NHC ligands and TPEDO activator

A facile method for selective N-(hetero)arylation of coordinating 3(5)-amino-1,2,4-triazoles under Pd/NHC catalysis using TPEDO as a new efficient Pd(ii) to Pd(0) reductant has been developed.

Heterocyclic Nitrilimines and Their Use in the Synthesis of Complex High-Nitrogen Materials

We show the ability of a nitrilimine prepared from 3-amino-5-nitro-1,2,4-triazole to undergo various cyclization and rearrangement reactions, giving a beautiful diversity of nitrogen-rich heterocyclic products. This chemistry includes the first cyclization of a nitrilimine with a diazonium species, giving a tetrazole, a previously unknown transformation, as well as leading to the creation of several new energetic materials with backbones not available by traditional techniques. New materials prepared were characterized both chemically (multinuclear NMR, IR, mass spectrometry, and elemental analysis) and energetically, with sensitivities and performances reported.

Divergent Synthesis of Substituted Amino-1,2,4-triazole Derivatives

A divergent efficient assembly of disubstituted 1,2,4-triazoles was established by cyclization of readily accessible N′-nitro-2-hydrocarbylidene-hydrazinecarboximidamides with moderate to excellent yields under mild reaction conditions. This divergent synthetic strategy was achieved simply by varying the reaction conditions. Under acidic conditions, amino-1,2,4-triazoles were obtained by an intramolecular redox reaction involving the NO2 group. Control experiments and DFT studies revealed that this transformation proceeds via an intramolecular 1,3-hydride transfer pathway leading to HNO2 elimination. Under neutral conditions with water as the solvent, nitroimino-1,2,4-triazoles were obtained by oxidative intramolecular annulation under air.

New methyl 5-(halomethyl)-1-aryl-1H-1,2,4-triazole-3-carboxylates as selective COX-2 inhibitors and anti-inflammatory agents: Design, synthesis, biological evaluation, and docking study

A new method was developed for synthesis of 1,2,4-triazole-3-carboxylates 5a-p and 6 from nitrilimines 3a-p through amination and heterocyclization two-steps reactions. All of 1,2,4-triazole-3-carboxylates 5 and 6 were characterized by spectroscopy technique. Based on the SAR study of anti-inflammation activity, most of these compounds showed potential anti-inflammatory activity on NO inhibition in LPS-induced RAW 264.7 cells (IC₅₀ < 7.0 µM) compared with Celecoxib and Indomethacin. Several potential compounds 5b-h, 5j, 5l, 5n, and 5o were subjected to in vitro cyclooxygenase COX-1/COX-2 inhibition assays. Compound 5d showed extraordinary COX-2 inhibition (IC₅₀ = 17.9 nM) and the best selectivity (COX-1/COX-2 = 1080). Furthermore, 5 mg/kg compound 5d exhibited better in vivo anti-inflammation and gastric protection results compared to 10 mg/kg Indomethacin. Docking experiments of 5d into COX-2 binding pocket have been evaluated. Following the bioactivities experimental data, the potential drug candidate 5d, significantly exhibited better anti-inflammatory effect than Indomethacin.

Understanding the 1,3-Dipolar Cycloadditions of Allenes

We have quantum chemically studied the reactivity, site-, and regioselectivity of the 1,3-dipolar cycloaddition between methyl azide and various allenes, including the archetypal allene propadiene, heteroallenes, and cyclic allenes, by using density functional theory (DFT). The 1,3-dipolar cycloaddition reactivity of linear (hetero)allenes decreases as the number of heteroatoms in the allene increases, and formation of the 1,5-adduct is, in all cases, favored over the 1,4-adduct. Both effects find their origin in the strength of the primary orbital interactions. The cycloaddition reactivity of cyclic allenes was also investigated, and the increased predistortion of allenes, that results upon cyclization, leads to systematically lower activation barriers not due to the expected variations in the strain energy, but instead from the differences in the interaction energy. The geometric predistortion of cyclic allenes enhances the reactivity compared to linear allenes through a unique mechanism that involves a smaller HOMO-LUMO gap, which manifests as more stabilizing orbital interactions.

Carbodiimide-based synthesis of N-heterocycles: moving from two classical reactive sites to chemical bond breaking/forming reaction

Carbodiimides are a unique class of heterocumulene compounds that display distinctive chemical properties. The rich chemistry of carbodiimides has drawn increasing attention from chemists in recent years and has made them exceedingly useful compounds in modern organic chemistry, especially in the synthesis of N-heterocycles. This review has outlined the extensive application of carbodiimides in the synthesis of N-heterocycles from the 1980s to today. A wide range of reactions for the synthesis of various types of N-heterocyclic systems (three-, four-, five-, six-, seven-, larger-membered and fused heterocycles) have been developed on the basis of carbodiimides and their derivatives.

Aminonitrones as highly reactive bifunctional synthons. An expedient one-pot route to 5-amino-1,2,4-triazoles and 5-amino-1,2,4-oxadiazoles – potential antimicrobials targeting multi-drug resistant bacteria

A four-component one-pot reaction proceeds very rapidly under mild conditions and gives the heterocyclic systems in good yields.

Amant C, Sun S, Xing Y. Synthesis of 1,2,4-oxadiazolidines via [3+2] cycloaddition of nitrones with carbodiimides

An efficient [3+2] cycloaddition of nitrones and carbodiimides has been developed.

Synthesis of 3-(5-amino-1H-1,2,4-triazol-3-yl)propanamides and their tautomerism

Two complementary pathways for the preparation of N-substituted 3-(5-amino-1H-1,2,4-triazol-3-yl)propanamides (5) were proposed and successfully realized in the synthesis of 20 representative examples. These methods use the same types of starting materials viz. succinic anhydride, aminoguanidine hydrochloride, and a variety of amines. The choice of the pathway and sequence of the introduction of reagents to the reaction depended on the amine nucleophilicity. The first pathway started with the preparation of N-guanidinosuccinimide, which then reacted with amines under microwave irradiation to afford 5. The desired products were successfully obtained in the reaction with aliphatic amines (primary and secondary) via a nucleophilic opening of the succinimide ring and the subsequent recyclization of the 1,2,4-triazole ring. This approach however failed when less nucleophilic aromatic amines were used. Therefore, an alternative pathway, with the initial preparation of N-arylsuccinimides and their subsequent reaction with aminoguanidine hydrochloride under microwave irradiation, was applied. The annular prototropic tautomerism in the prepared 1,2,4-triazoles 5 was studied using NMR spectroscopy and X-ray crystallography.

Two complementary pathways for the preparation of N-substituted 3-(5-amino-1H-1,2,4-triazol-3-yl)propanamides were proposed and successfully realized in the synthesis of 20 representative examples.