Regiospecific solid-phase synthesis of substituted 1,2,3-triazoles

A traceless and regiospecific solid-phase synthesis of substituted 1,2,3-triazoles is developed using polystyrene-sulfonyl hydrazide resin. The chemistry is applicable to combinatorial library synthesis.     

Substituted 1-(isoxazol-3-yl)methyl-1H-1,2,3-triazoles: Synthesis,palladium(II) complexes,and high-turnover catalysis in aqueous media

New substituted 3-((1H-1,2,3-triazol-1-yl)methyl)-5-arylisoxazoles (aryl?=?Ph, p-Tol) and 2-(5-phenylisoxazol-3-yl)-5-(2-(1-((5-(p-tolyl)isoxazol-3-yl)methyl)-1H-1,2,3-triazol-4-yl)ethyl)-1,3,4-oxadiazole were synthesized by means of click-chemistry procedures. The obtained compounds were used as ligands in preparation of palladium(II) complexes, and the latter proved to be high-turnover-number catalysts for CC cross-coupling reactions under Green Chemistry conditions. One of the ligands was structurally characterized by single crystal X-ray diffraction, and the structure of complexes was determined by ¹H, ¹³C, ¹⁵N NMR spectroscopy and quantum-chemical modeling.     

Tandem synthesis of 1-formyl-1,2,3-triazoles

A tandem method for preparing 4-formyl-1,2,3-triazoles via a two-step one-pot acetal cleavage/CuAAC reaction was developed. Using this method, 4-formyl-1,2,3-triazole analogs with both electron-withdrawing and electron-donating substituents were prepared in good yield and purity. Expansion of this method to a three-step tandem reaction that incorporates an additional step of azide substitution was also successful, circumventing the need for organic azide isolation. This one-pot method, noteworthy in its simplicity and mild conditions, utilizes practical, readily available reactants and relies on protic solvent to promote acid-catalyzed acetal cleavage.     

The one-pot synthesis of 4-aryl-1H-1,2,3-triazoles without azides and metal catalization

In this study, a new methodology for the one-pot synthesis of 4-aryl-1H-1,2,3-triazoles from arylglyoxaldoxime semicarbazone is presented. 4-Aryl-1,2,3-triazoles were obtained in moderate to good yields via sodium dithionite and O₂, which are all efficient, safe and inexpensive reagents. This reaction is more suitable for large-scale syntheses than those using hydrazoic acid, sodium azide, or organic azides.     

Reaction of N-fluoropyridinium fluoride with isonitriles and diazo compounds: a one-pot synthesis of (pyridin-2-yl)-1H-1,2,3-triazoles

Reaction of N-fluoropyridinium fluoride generated in situ with a series of isonitriles and diazo compounds led to the formation of the corresponding (pyridine-2-yl)-1H-1,2,3-triazoles in good yields (37-59%). Best outcome was consistently achieved with both aromatic isonitriles and stabilized diazo derivatives. The proposed reaction mechanism involves the intermediate formation of a highly reactive carbene species.     

On the explosive properties of 1H-benzotriazole and 1H-1,2,3-triazole

For 1H-benzotriazole, no explosive properties are observable, but the relative high exothermic decomposition energy of 1590 J/g should be kept in mind. Nevertheless, an endothermic melting barrier at 100 °C ensures safe handling at lower temperatures. For 1H-1,2,3-triazole, the exothermic decomposition energy is as high as 2600 J/g, but explosive properties are also not detectable. Therefore, both reagents are hazardous with regard to the exothermic decomposition potential and can be handled safely with precautions.     

Synthesis of 5-organostibano-1H-1,2,3-triazoles by Cu-catalyzed azide-alkyne cycloaddition and their application in the acyl-induced deantimonation for the preparation of fully substituted 5-acyl-1,2,3-triazoles

The Cu-catalyzed azide-alkyne cycloaddition by the reaction of various ethynylstibanes with benzylazide in the presence of CuBr (5 mol%) under aerobic conditions led to the formation of trisubstituted 5-organostibano-1H-1,2,3-triazoles. Further, the acyl-induced deantimonation of 5-stibanotriazoles with acyl chlorides in the presence of N,N-dimethyl-4-aminopyridine and triethylamine afforded the corresponding trisubstituted 5-acyltriazoles in moderate-to-good yields.     

A tandem of the Cornforth rearrangements of 4-(1,2,3-triazol-1-yl)iminomethyl-1,2,3-thiadiazole

The method for the synthesis of 5-(2,6-dimethylmorpholino)-1,2,3-thiadiazole-4-carbaldehyde was proposed. Its reaction with sodium 1-amino-4-(N-methyl)carbamoyl-1,2,3-triazol-5-olate proceeds through a tandem of the Cornforth rearrangements. The initially formed azomethine isomerizes into sodium 4"-(2,6-dimethylmorpholino)thiocarbonyl-4-(N-methyl)carbamoyl-1,1"-bis[1,2,3]triazolyl-5-olate, which then rearranges to give sodium 4-{N-[4-(2,6-dimethylmorpholinothiocarbonyl)-1,2,3-triazol-1-yl]carbamoyl}-1-methyl-1,2,3-triazol-5-olate.     

Synthesis of 1,2,3,4-tetrazine 1,3-dioxides annulated with 1,2,3-triazoles and 1,2,3-triazole 1-oxides

1,2,3,4-Tetrazine 1,3-dioxides annulated with 1,2,3-triazoles and 1,2,3-triazole 1-oxides have been synthesized by the reaction of 4-amino-5-(tert-butyl-NNO-azoxy)-2-R-2H-1,2,3-triazoles (R=Me, i-Pr, t-Bu) and their 1-oxides (R=H, Me, Et, i-Pr) with the HNO₃/H₂SO₄/Ac₂O system. Their thermal stability, spectroscopic, and X-ray properties have been studied.     

Preparation of 4,5 disubstituted-2H-1,2,3-triazoles from (Z)-2,3-diaryl substituted acrylonitriles

2H-1,2,3-Triazoles (2) were synthesized by [3+2] cycloaddition of (Z)-2,3-diaryl substituted acrylonitriles (1) with sodium azide and ammonium chloride in DMF/water. This method represents a facile and efficient reaction procedure for the synthesis of 4,5-diaryl-2H-1,2,3-triazoles in modest to good yields.     

Synthesis and Characterization of Novel 2-(1,2,3-Triazol-4-yl)-4,5-dihydro-1H-pyrazol-1-yl)thiazoles and 2-(4,5-Dihydro-1H-pyrazol-1-yl)-4-(1H-1,2,3-triazol-4-yl)thiazoles

Reactions of 1-(5-methyl)-1H-1,2,3-triazol-4-yl)ethan-1-ones and benzaldehydes in ethanol under basic conditions gave the corresponding chalcones. Reactions of the chalcones combined with thiosemicarbazide in dry ethanol containing sodium hydroxide afforded the corresponding pyrazolin-N-thioamides. Reactions of the synthesized pyrazolin-N-thioamides and several ketones (namely, ethyl 2-chloro-3-oxobutanoate, 2-bromoacetylbenzofuran, and hydrazonoyl chloride) gave the corresponding novel 2-(1,2,3-triazol-4-yl)-4,5-dihydro-1H-pyrazol-1-yl)thiazoles in high yields (77–90%). Additionally, 2-(4,5-dihydro-1H-pyrazol-1-yl)-4-(1H-1,2,3-triazol-4-yl)thiazoles were obtained in high yields (84–87%) from reactions with N-pyrazoline-thioamides and 4-bromoacetyl-1,2,3-triazoles under basic conditions. The structures of six of the newly synthesized heterocycles were confirmed by X-ray crystallography.     

Synthesis and Biological Activity of Novel 1-Substituted Phenyl(glycosyl)-4-{4-[(4,6-dimethoxy)pyrimidin-2-yl] Piperazin-1-yl}methyl-1H-1,2,3-triazoles

A series of novel 1-substituted phenyl or glycosyl 1,2,3-triazoles was designed and synthesized by azide-alkyne 1,3-dipolar cycloaddition between 4,6-dimethoxy-2-[(4-prop-2-ynyl)piperazin-1-yl]pyrimidine and each of different azides catalysed by in situ generated Cu(I). The O-acyl protecting groups on glycosyl 1,2,3-triazoles were removed by triethylamine in wet methanol. Their chemical structures were established on the basis of corresponding ¹H NMR, ¹³C NMR, MS and elemental analysis. The fungicidal activities of target compounds were evaluated in vitro against Fusarium omysporum, Physalospora piricola, Alternaria solani, Phytophthora capsici, Cercospora arachidicola and Gibberella zeae at 50 μg/mL. The bioassay results indicate that some of the compounds exhibited mode-rate but promising fungicidal activities. In particular, acetylated glucopyranosyl triazole displayed a good fungicidal activity against Physalospora piricola, which is equal to that of the positive control compound chlorothalonil.     

Magnetically recoverable copper ferrite catalyzed cascade synthesis of 4-Aryl-1H-1,2,3-triazoles under microwave irradiation

Magnetically active CuFe₂O₄ catalyzed cascade synthesis of 4-Aryl-1H-1,2,3-triazoles under microwave irradiation starting from aromatic aldehydes, sodium azide and nitromethane has been developed and demonstrated here. The catalyst system needed for the purpose was prepared following a procedure by A. Dandiya et al. with a slight modification and was characterized using FT-IR, XRD, SEM-EDX and TEM analysis. The most notable advantage of the developed methodology is the excellent time economy to carry out the transformation. Other features include simple operating procedure, wide substrate coverage and easy recovery of the catalyst. Reusability of the catalyst has been tested and found to be very satisfactory up to sixth cycle without significant loss in efficiency. All the synthesized compounds have been characterized using FTIR, ¹H & ¹³CNMR spectroscopy, HRMS.     

Efficient Pd(0)-catalyzed synthesis of 1,2,3-triazolo-3′-deoxycarbanucleosides and their analogues

The racemic synthesis of hitherto unknown 5-substituted-[1,2,3]-triazolo-3′-deoxycarbanucleosides and [1,2,3]-triazolo-[4,5-c]pyridin-4-one analogues is described. The key iodinated intermediate 10 was prepared in 10 steps using a malonic synthesis. Various alkynes were introduced at the C-5 position of 10 under optimized Pd(0)-catalyzed Sonogashira cross-coupling alkynylation to yield after deprotection 12a-i. The synthesis of their 8-aza-3-deazapurine analogues (13a-h) was also accomplished through the heteroannulation of internal alkynes under aqueous dimethylamine.     

Efficient synthesis of 5-fluoroalkylated 1H-1,2,3-triazoles and application of the bromodifluoromethylated triazole to the synthesis of novel bicyclic gem-difluorinated 1H-pyrano[3,4-d][1,2,3]-triazol-4-one compounds

A series of 5-fluoroalkylated 1H-1,2,3-triazoles were synthesized in good yield by the regiospecific 1,3-dipolar cycloaddition reaction of (Z)-ethyl 3-fluoroalkyl-3-pyrrolidino-acrylates with aryl or benzyl azides. In the cases of benzyl azides, addition of Na₂CO₃ was crucial for a high yield of the triazoles. Tetrakis(dimethylamino)ethylene (TDAE) promoted reaction of bromodifluoro-methylated triazole with aldehydes affording a new class of β,β-difluoro-β-triazolyl alcohol derivatives, which were lactonized with catalytic amount of p-toluenesulfonic acid in toluene at 80-90°C to give a series of novel bicyclic gem-difluorinated 1H-pyrano[3,4-d][1,2,3]-triazol-4-one compounds in good yield.     

A new synthetic method for the 2H-[1,2,3]thiadiazolo[5,4-b]indoles

The systematic study of oxidative cyclization of 3-hydrazono-1,3-dihydroindole-2-thiones has been carried out and a series of new 2H-[1,2,3]thiadiazolo[5,4-b]indoles has been prepared. The elaborated reaction represents an efficient method for the synthesis of fused 1,2,3-thiadiazoles.     

2-(1,2,3-Triazol-4-yl)pyridine-containing ethynylarenes as selective ‘turn-on’ fluorescent chemosensors for Ni(II)

A series of ethynylarene compounds containing 2-(1,2,3-triazol-4-yl)pyridine chelating units were studied as fluorescent chemosensors for metal cations in aqueous solution. Analogs possessing two chelating units bridged by either 1,4-diethynylphenyl or 2,7-diethynylnaphthyl subunits displayed large hypsochromic shifts coupled with signal intensification when exposed to increasing concentrations of Ni(II), a unique response among 22 metal cation analytes. This response was shown to be reversible, and is proposed to derive from disruption of aggregate formation upon Ni(II) binding at the peripheral chelating units.     

Synthesis of novel 2,3-substituted quinazolin-4-ones by condensation of alkyl or aromatic diamines with 5-(N-arylimino)-4-chloro-5H-1,2,3-dithiazoles

The work described in this paper is a further example of the utility of Appel's salt in the conception of novel heterocyclic rings. We confirmed that primary alkyldiamines may react easily with the methyl N-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)-anthranilates to afford quinazolines, which are very interesting starting materials for the access to novel 2,3-condensed quinazolin-4-ones. On the other side, aromatic amines allow the synthesis of polycyclic molecules, which are structurally close to the model natural products (e.g., rutaecarpine, luotonine, tryptanthrine and vasicinone).     

Synthesis of substituted 4-(1H-indol-6-yl)-1H-indazoles as potential PDK1 inhibitors

The development of a preparative route to a series of novel 4-(1H-indol-6-yl)-1H-indazole compounds as potential PDK1 inhibitors is described. The synthetic strategy centres on the late-stage Suzuki cross-coupling of N-unprotected indazole and indole fragments. The use of a monoligated palladium catalyst system was found to be highly beneficial in the cross-coupling reaction. The indazole and indole fragments were constructed by diazotisation/cyclisation and S_NAr/reductive cyclisation sequences, respectively.