An alternatively metal-free synthesis of 1,3,5-triazines or 1,2,4-thiadiazoles from benzyl chlorides and benzylamines mediated by elemental sulfur

Sustainable Synthesis of Substituted 1,3,5-Triazines by [ONO]-Pincer-Supported Nickel(II) Complexes via an Acceptorless Dehydrogenative Coupling Strategy

A facile, cost-effective, and sustainable synthesis of substituted triazines from primary alcohols by newly synthesized nickel pincer-type complexes (1-3) has been described. Herein, we report the synthesis of a set of three well-defined Ni(II) O^N^O pincer-type complexes, structurally characterized by analytical, spectral, and X-ray diffraction techniques. Further, the nickel complexes are explored as efficient catalysts (4 mol %) for the construction of 2,4,6-substituted 1,3,5-triazines from readily available alcohols via an acceptorless dehydrogenative coupling (ADC) strategy. A wide range of substituted triazine derivatives (33 examples) has been synthesized from the coupling of alcohols and benzamidine/guanidine hydrochloride with a maximum isolated yield of 92% under mild conditions, with eco-friendly H2O and H2 gas as the only byproducts. A plausible mechanism has been proposed based on a sequence of control experiments. Interestingly, the short synthesis of the antiulcer drug irsogladine and the large-scale synthesis of 2,4-diphenyl-6-(p-tolyl)-1,3,5-triazine highlight the convenience of the current methodology.

Functionalized Triazines and Tetrazines: Synthesis and Applications

The molecules possessing triazine and tetrazine moieties belong to a special class of heterocyclic compounds. Both triazines and tetrazines are building blocks and have provided a new dimension to the design of biologically important organic molecules. Several of their derivatives with fine-tuned electronic properties have been identified as multifunctional, adaptable, switchable, remarkably antifungal, anticancer, antiviral, antitumor, cardiotonic, anti-HIV, analgesic, anti-protozoal, etc. The objective of this review is to comprehensively describe the recent developments in synthesis, coordination properties, and various applications of triazine and tetrazine molecules. The rich literature demonstrates various synthetic routes for a variety of triazines and tetrazines through microwave-assisted, solid-phase, metal-based, [4+2] cycloaddition, and multicomponent one-pot reactions. Synthetic approaches contain linear, angular, and fused triazine and tetrazine heterocycles through a combinatorial method. Notably, the triazines and tetrazines undergo a variety of organic transformations, including electrophilic addition, coupling, nucleophilic displacement, and intramolecular cyclization. The mechanistic aspects of these heterocycles are discussed in a detailed way. The bioorthogonal application of these polyazines with various strained alkenes and alkynes provides a new prospect for investigations in chemical biology. This review systematically encapsulates the recent developments and challenges in the synthesis and possible potential applications of various triazine and tetrazine systems.

Ligand centered redox enabled sustainable synthesis of triazines and pyrimidines using a zinc-stabilized azo-anion radical catalyst

Herein, we report ligand-centered redox controlled Zn(II)-catalyzed multicomponent approaches for synthesizing pyrimidines and triazines. Taking advantage of the ligand-centered redox events and using a well-defined Zn(II)-catalyst (1a) bearing (E)-2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline (L1a) as the redox-active ligand, a wide variety of substituted pyrimidines and triazines were prepared via dehydrogenative alcohol functionalization reactions. Pyrimidines were prepared via two pathways: (i) dehydrogenative coupling of primary and secondary alcohols with amidines and (ii) dehydrogenative coupling of primary alcohols with alkynes and amidines. Triazines were prepared via dehydrogenative coupling of alcohols and amidines. Catalyst 1a is well tolerant to a wide range of substrates yielding the desired pyrimidines and triazines in moderate to good isolated yields. A series of control reactions were performed to predict the plausible mechanism, suggesting that the active participation of the ligand-centered redox events enables the Zn(II)-complex 1a to act as an efficient catalyst for synthesizing these N-heterocycles. Electron transfer processes occur at the azo-aromatic ligand throughout the catalytic reaction, and the Zn(II)-center serves only as a template.

Optoelectronic and charge transport properties of D-n-A type 1,3,5-triazine derivatives: A combined experimental and DFT study

The synthesis of five D-n-A type star-shaped octupolar molecules is presented in the current work. The exploration of the potential applicability of molecules under study in organic optoelectronics as electron or hole transporting materials is carried out by DFT methods. All the molecules have a 1,3,5-triazine core, which acts as an electron acceptor (A). Phenyl ring and pyridine ring act as electron donors (D) in AZ and PZ series of molecules respectively. The donor and acceptor core are connected by -NH bridge (n). The crystal structure of a molecule in the PZ series is elucidated. Thermogravimetric studies are carried out to confirm the thermal stability of molecules. The frontier molecular orbitals of molecules are characterized with the help of cyclic voltammetry. With the assistance of DFT methodologies, the whole research presented in this work focuses on the electronic excitations, reorganization energies, electron affinity, ionization potential and features of frontier molecular orbitals of molecules. The investigation of the variation of optoelectronic properties of molecules with changing patterns of nucleophilic substitution on 1,3,5-triazine core and presence of a hetero (nitrogen) atom in the donor part of the molecule is also accomplished.

Chromatography-Free Multicomponent Synthesis of Thioureas Enabled by Aqueous Solution of Elemental Sulfur

The development of a new three-component chromatography-free reaction of isocyanides, amines and elemental sulfur allowed us the straightforward synthesis of thioureas in water. Considering a large pool of organic and inorganic bases, we first optimized the preparation of aqueous polysulfide solution from elemental sulfur. Using polysulfide solution, we were able to omit the otherwise mandatory chromatography, and to isolate the crystalline products directly from the reaction mixture by a simple filtration, retaining the sulfur in the solution phase. A wide range of thioureas synthesized in this way confirmed the reasonable substrate and functional group tolerance of our protocol.