Synthesis of Pentafluorosulfanylpyrazole and Pentafluorosulfanyl-1,2,3-triazole and Their Derivatives as Energetic Materials by Click Chemistry

Hydroamination of Triisopropylsilyl Acetylene Sulfur Pentafluoride - a Bench-top Route to Pentafluorosulfanylated Enamines

Synthetic access to a variety of aliphatic and vinylic pentafluorosulfanylated building blocks remains a major challenge in contemporary organofluorine chemistry hampering its investigation in the context of medicinal chemistry, agrochemistry and functional materials. Herein, we report a bench-top protocol to access the virtually unknown class of α-SF5 -enamines under mild reaction conditions in good to excellent yields (up to 95 %). This reaction combines the protodesilylation of the commercially available precursor TASP with the in situ hydroamination of HC≡C-SF5 . The on-site use of highly toxic gases or corrosive reagents is avoided, making access to this motif applicable to a wide chemical audience. The excellent E-diastereoselectivity of this two-step cascade reaction is suggested to be the result of the convergence of the fast Z-/E- isomerization of a vinyl anion as well as the isomerization of the iminium ion. The remarkable thermal stability of these SF5 -enamines encourages further studies of their synthetic utility.

Synthesis of Substituted Pentafluorosulfanylpyrazoles Under Flow Conditions

The development of flow conditions for the synthesis of pentafluorosulfanylpyrazoles is reported. A range of alkyl- and aryl-substituted SF5-alkynes were used in combination with different diazoacetates for this transformation. The corresponding substituted SF5-pyrazoles were obtained in up to 90% yield (average of 74% for 21 examples) as a mixture of isomers (up to 73:27 ratio). Synthetic transformations starting from an SF5-containing pyrazole were also demonstrated.

Recent Advances in Copper-Based Solid Heterogeneous Catalysts for Azide-Alkyne Cycloaddition Reactions

The copper(I)-catalyzed azide−alkyne cycloaddition (CuAAC) reaction is considered to be the most representative ligation process within the context of the “click chemistry” concept. This CuAAC reaction, which yields compounds containing a 1,2,3-triazole core, has become relevant in the construction of biologically complex systems, bioconjugation strategies, and supramolecular and material sciences. Although many CuAAC reactions are performed under homogenous conditions, heterogenous copper-based catalytic systems are gaining exponential interest, relying on the easy removal, recovery, and reusability of catalytically copper species. The present review covers the most recently developed copper-containing heterogenous solid catalytic systems that use solid inorganic/organic hybrid supports, and which have been used in promoting CuAAC reactions. Due to the demand for 1,2,3-triazoles as non-classical bioisosteres and as framework-based drugs, the CuAAC reaction promoted by solid heterogenous catalysts has greatly improved the recovery and removal of copper species, usually by simple filtration. In so doing, the solving of the toxicity issue regarding copper particles in compounds of biological interest has been achieved. This protocol is also expected to produce a practical chemical process for accessing such compounds on an industrial scale.

NHC-catalysed [3 + 2]-asymmetric annulation between pyrazolin-4,5-diones and enals: synthesis of novel spirocyclic pyrazolone γ-butyrolactones and computational study of mechanism and stereoselectivity

Herein we present the first asymmetric synthesis of spiropyrazolone γ-butyrolactones from 1H-pyrazol-4,5-diones and enals by an NHC-catalysed [3 + 2] annulation. DFT calculations carried out predict the experimental configuration of final adducts.

4,5-Dicyano-1,2,3-Triazole-A Promising Precursor for a New Family of Energetic Compounds and Its Nitrogen-Rich Derivatives: Synthesis and Crystal Structures

The nitrogen-rich compounds and intermediates with structure of monocyclic, bicyclic, and fused rings based on 1,2,3-triazole were synthesized and prepared by using a promising precursor named 4,5-dicyano-1,2,3-triazole, which was obtained by the cyclization reaction of diaminomaleonitrile. Their structure and configurational integrity were assessed by Fourier transform-infrared spectroscopy (FT-IR), mass spectrometry (MS), and elemental analysis (EA). Additionally, fourteen compounds were further confirmed by X-ray single crystal diffraction. Meanwhile, the physical properties of four selected compounds (3·H₂O, 6·H₂O, 10·H₂O, and 16) including thermal stability, detonation parameters, and sensitivity were also estimated. All these compounds could be considered to construct more abundant 1,2,3-triazole-based neutral energetic molecules, salts, and complex compounds, which need to continue study in the future in the field of energetic materials.

Synthesis and [3,3]-sigmatropic rearrangements of 5-(pentafluorosulfanyl)-pent-3-en-2-ol, its homologues, and trifluoromethyl analogues

The synthesis of aliphatic (pentafluoro-λ6-sulfanyl)(SF5)-substituted compounds is more challenging than that of the related CF3-substituted analogues. Previous investigations of [3,3]-sigmatropic rearrangements of γ-SF5-substituted allylic alcohols failed to yield 3-SF5-substituted carboxylic acid derivatives. Herein, we present the synthesis of a series of 1-SF5-alk-1-en-3-ols and our efforts to apply them in Johnson-Claisen, ester enolate-Claisen, and Ireland-Claisen rearrangements. Unfortunately, these reactions failed to include the 1-SF5-substituted 1,2-double bond, although successful reactions of analogous CF3-allylic alcohols were reported. Further experiments revealed that bulkiness rather than electronic properties of the SF5 group prevented [3,3]-sigmatropic rearrangements. Indeed, the introduction of a competing second vinyl group into the system (1-SF5-penta-1,4-dien-3-ol) confirmed that a Johnson-Claisen rearrangement was successful (92% yield of methyl 7-SF5-hepta-4,6-dienoate) with incorporation of the unsubstituted 4,5-double bond while the 1-SF5-substituted 1,2-double bond remained unchanged. Efforts to apply 1-(SF5CF2)-substituted 1,2-double bond systems, which are similar to CF3 analogues in steric requirements, in Johnson-Claisen or ester enolate-Claisen rearrangements failed because of the instability of the SF5CF2 substituent under various reaction conditions. On the other hand, when the SF5 group was separated from the reaction center by a CH2 group instead (5-SF5-pent-3-en-2-ol), Johnson-Claisen rearrangements using six orthoesters provided the target 2-substituted 3-(CH2SF5)-hex-4-enoates in 55-76% yields as ∼1 : 1 mixtures of diastereomers. As an example to demonstrate the utility of these products, methyl 3-(CH2SF5)-hex-4-enoate was reduced, and the formed alcohol was oxidized to the aldehyde. Finally, initial experiments showed that the synthetic sequence developed for SF5 compounds is also applicable for analogous CF3-substituted allylic alcohols (5-CF3-pent-3-en-2-ol) and their Johnson-Claisen rearrangement.

Selective Synthesis of Bis(3-(3-(trifluoromethyl)-1H-1,2,4-triazol-5-yl)-4,4'-azo- and -azoxyfurazan Derivatives

In this paper, we report the synthesis of two new derivatives, bis(3-(3-(trifluoromethyl)-1H-1,2,4-triazol-5-yl)-4,4'-azo- and -azoxyfurazans by selective oxidation of 4-(3-(trifluoromethyl)-1H-1,2,4-triazol-5-yl)-1,2,5-oxadiazol-3-amine. Ammonium salts of these derivatives were prepared, and all of them were fully characterized by multinuclear NMR, FTIR spectroscopy, elemental analysis, differential scanning calorimetry (DSC), and single-crystal X-ray diffraction. All of the new compounds have high measured crystal densities, and the energetic properties have been investigated.

Recent approaches towards one-carbon homologation-functionalization of aldehydes

One-carbon homologation-functionalization in organic synthesis is a quite challenging and difficult task in terms of atom economy, ease of reaction, selectivity and number of steps involved. Due to the reactivity associated with most classes of carbonyls, these groups have always attracted a great deal of attention from synthetic chemists to transform them into various functionalities. In this context various researchers developed new methods for one-carbon extension-functionalization of carbonyls that serve as effective synthetic methodologies and are widely used in target-oriented and natural product synthesis. On account of the vast applicability associated with these transformations, herein we seek to summarize and highlight the important synthetic achievements in this advancing arena for various one-carbon homologation cum functionalization reactions of aldehydes and deep dive into some modern approaches adopted by organic chemists.

Synthesis of vinyl-1,2,3-triazole derivatives under transition metal-free conditions

Synthesis of vinyl triazole derivatives with alkynes and triazoles promoted by an inorganic base under transition metal-free conditions is reported.

Thermochemistry and Initial Decomposition Pathways of Triazole Energetic Materials

A thorough investigation of the initial decomposition pathways of triazoles and their nitro-substituted derivatives has been conducted using the MP2 method for optimization and DLPNO-CCSD(T) method for energy. Different initial thermolysis mechanisms are proposed for 1,2,4-triazole and 1,2,3-triazole, the two kinds of triazoles. The higher energy barrier of the primary decomposition path of 1,2,4-triazole (H-transfer path, ∼52 kcal/mol) compared with that of 1,2,3-triazole (ring-open path, ∼45 kcal/mol) shows that 1,2,4-triazole is more stable, consistent with experimental observations. For nitro-substituted triazoles, more dissociation channels associated with the nitro group have been obtained and found to be competitive with the primary decomposition paths of the triazole skeleton in some cases. Besides, the effect of the nitro group on the decomposition pattern of the triazole skeleton has been explored, and it has been found that the electron-withdrawing nitro group has an opposite effect on the primary dissociation channels of 1,2,4-triazole derivatives and 1,2,3-triazole derivatives.

Computational study of energetic derivatives of 3,3′-bridged ditriazoles

A series of energetic bridged ditriazole was designed by incorporating different bridges and substituents into 4H-1,2,4-triazole ring. The geometrical structures, heats of formation, detonation properties, electronic structures, thermodynamic properties, free spaces, impact sensitivities, and thermal stabilities of the designed compounds were evaluated by employing density functional theory. The results elucidate that the –N3 substituent and –N=N– bridge can sufficiently increase their heats of formation. The calculated values of detonation properties show that –NF2, –ONO2, –O–, and –N=N(O)– are useful structural fragments to improve their detonation performance. The incorporation of the oxy (–O–) bridge increases their HOMO–LUMO energy gaps. An analysis of h50 values indicate that most of the designed compounds are less sensitive. The N(ring)-NO2 bond in the majority of the derivatives may be a possible trigger bond in thermal decomposition process. The incorporation of –CH2–CH2– and –O– is helpful to enhance their thermal stabilities. Based on appropriate thermal stabilities and superb detonation properties, six compounds were screened as promising high energy density compounds.

Effect of Fluoro Substituents on Polynitroarylenes: Design, Synthesis and Theoretical Studies of Fluorinated Nitrotoluenes

The replacement of traditional polynitroarylenes by their fluorinated derivatives has attracted great attention due to the improvements on detonation performance caused by the fluorine effect. A straightforward synthesis of three novel fluorinated nitrotoluenes with different degrees of nitration was achieved under selected high temperatures. The fluorine exerted remarkable influence on the nitration process through the electron-withdrawing effect and a mechanism of the transformation was proposed according to the experimental results. Thermal decomposition behavior of the fluorinated nitrotoluenes was investigated by differential scanning calorimetry and all the compounds showed ideal low melt points for the melt-cast process. X-ray analysis of the fluorinated derivatives were carried out as well as density functional calculations to establish the electronic density and electrostatic potential on the molecular surface of the optimized structures. The good thermal and detonation properties make the newly developed fluorinated nitrotoluenes possible replacements for trinitrotoluene and dinitrotoluene in the formation of melt-cast energetic materials.

Pyridine tetrafluoro-λ6-sulfanyl chlorides: spontaneous addition to alkynes and alkenes in the presence or absence of photo-irradiation

A radical addition reaction of Py-SF₄Cl to alkynes and alkenes provide pyridine-SF₄-alkenes and pyridine-SF₄-alkanes under blue LED light irradiation or absence of light irradiation in CPME or without solvent.

Palladium-catalyzed oxidative homocoupling of pyrazole boronic esters to access versatile bipyrazoles and the flexible metal–organic framework Co(4,4′-bipyrazolate)

A facile catalytic protocol achieves the homocoupling of pyrazole boronic esters, enabling access to the structurally-flexible metal–organic framework Co(bpz).

Synthesis of N-Arylpyrazoles by Palladium-Catalyzed Coupling of Aryl Triflates with Pyrazole Derivatives

A method for the synthesis of N-arylpyrazoles by palladium-catalyzed coupling of aryl triflates with pyrazole derivatives is described. Using tBuBrettPhos as a ligand, the palladium-catalyzed C-N coupling of a variety of aryl triflates including ortho-substituted ones with pyrazole derivatives proceeded efficiently to give N-arylpyrazole products in high yields. 3-Trimethylsilylpyrazole was found to be an excellent pyrazole substrate for the coupling, and the corresponding product, 1-aryl-3-trimethylsilylpyrazole, also served as a great template for the syntheses of N-arylpyrazole derivatives, as demonstrated by regioselective halogenation at the 3-, 4-, and 5-positions of the pyrazole ring.

Surface plasmon resonances enhanced click chemistry through synergistic photothermal and hot electron effects

Surface plasmon resonance excitation on Au enhances a visible light-assisted click reaction through synergistic photothermal and hot electron effects.

Synthesis of aryl and heteroaryl tetrafluoro-λ6-sulfanyl chlorides from diaryl disulfides using trichloroisocyanuric acid and potassium fluoride

A catalyst-free method for the synthesis of (Het)ArSF₄Cl by using trichloroisocyanuric acid and potassium fluoride in acetonitrile is disclosed.

A nitrogen-rich ligand as a scaffold for slow magnetic relaxation in dysprosium-based 0D and 1D architectures

A recently designed nitrogen-rich ligand is successfully applied as a scaffold for lanthanide ions to show that the intricate chemistry of energetic materials can be combined with other fields of research, including that of molecular magnetism. Herein, we report the synthesis of two different types of molecular architectures using a single ligand template, in which the discrete monomer exhibits single-molecule magnet-like behaviour along with two well-isolated modes of magnetic relaxation.

An eccentric rod-like linear connection of two heterocycles: synthesis of pyridine trans-tetrafluoro-λ6-sulfanyl triazoles

The trans-tetrafluoro-λ6-sulfane (SF4) group has been utilized as a unique three-dimensional building block for the linear connection of two independent N-heterocycles, pyridines and triazoles. The linearly connected heterocyclic compounds were synthesized by thermal Huisgen 1,3-dipolar cycloaddition between previously unknown pyridine SF4-alkynes and readily available azides, providing a series of rod-like SF4-connected N-heterocycles in good to excellent yields. X-ray crystallographic analysis of the target products revealed the trans-geometry of the SF4 group, which linearly connects two independent N-heterocycles. This research will open the field of chemistry of SF4-connected heterocyclic compounds.