Diazotization of o-Aminoamidoximes for the Preparation of Energetic 6,5,6-Fused 1,2,3-Triazine-3-oxides.

Two 6,5,6-fused 1,2,3-triazine-3-oxides (4 and 6) were designed and synthesized via the reaction of o-aminoamidoximes with sodium nitrite. In addition, the ring-opening products (5, 7, and 8) derived from 1,2,3-triazine-3-oxides were isolated and characterized. A comprehensive exploration of the reaction mechanism governing the ring-opening process was performed through a combination of theoretical and experimental studies. Notably, compound 4 exhibited commendable detonation properties and low sensitivity, demonstrating its promising potential as an energetic material.

N-Benzylhydroxylamine as a novel synthetic block in "C1N1" embedding reaction via α-C(sp3)-H activation strategy.

A novel process using N-benzylhydroxylamine hydrochloride as a "C1N1 synthon" in [2+2+1] cyclization for the construction of 1,2,5-trisubstituted imidazoles has been described for the first time. The key to realizing this process lies in capturing arylamines by in situ generated novel acyl ketonitrone intermediates. Subsequent tautomerization activates the α-C(sp3)-H of N-benzylhydroxylamines, and thus breaks through its inherent reaction mode and achieves N, α-C site-selective cyclization. Furthermore, this method enables scale-up synthesis and late-stage modification of complex molecules.

I2-DMSO-Mediated Construction of 2,3- and 2,4-Disubstituted Pyrimido[1,2-b]indazole Skeletons.

An efficient synthetic method for constructing 2,3- and 2,4-disubstituted pyrimidio[1,2-b]indazole skeletons through I2-DMSO-mediated and substrate-controlled regioselective [4 + 2] cyclization is reported. The reaction conditions are mild, its operation is simple, and the substrate scope is wide. More than 60 pyrimidio[1,2-b]indazole derivatives have been synthesized, providing a new methodology for constructing related molecules and potentially enriching bioactive-molecule libraries.

Pushing the limits of the heat of detonation via the construction of polynitro bipyrazole.

The trinitromethyl group is a highly oxidized group that is found as an active functionality in many high-energy-density materials. The most frequently used previous synthetic method for the introduction of the trinitromethyl group is the nitration of heterocyclic compounds containing an acetonyl/ethyl acetate/chloroxime group. Now a novel strategy for constructing a trinitromethyl group (5) via nitration of an ethylene bridged compound, dipyrazolo[1,5-a:5',1'-c]pyrazine (2), is reported. In addition, the other two nitrated products (3 and 4) were obtained under different nitrating conditions. Compound 5 has excellent detonation performance (Dv = 9047 m s-1, P = 35.6 GPa), and a low mechanical sensitivity (IS = 10 J, FS = 216 N), with an especially attractive heat of detonation of 6921 kJ kg-1, which significantly exceeds that of the state-of-the-art explosive CL-20 (Q: 6162 kJ kg-1).

From Tetranitromethane to Gem-Dinitro-Bridged Nitrogen-Rich Heterocyclic Compound: Achieving High Heat of Detonation.

Improving the detonation performance of tetranitromethane (TNM) by introducing energetic moieties is an intriguing area in the field of energetic materials. Incorporation of a mono nitrogen-rich skeleton into TNM usually results in unsatisfactory detonation performance. Now, we reported the design and synthesis of an advanced TNM-like molecule (3) containing nitrogen-rich triazole and nitro-triazinane moieties. In addition, two of its analogues (4 and 5) were also obtained. Taking advantage of the positive heat of formation brought by triazole and triazinane rings and high-density properties donated by many nitro groups, 3 shows promising heat of detonation (Q = 5859 kJ kg-1), which is 2.8 times of TNM and higher than most of its mono ring-modified derivatives (Q: 2076 to 5594 kJ kg-1). The detonation velocity and detonation pressure of 3 (Dv = 8964 m s-1 and P = 35.7 GPa) are competitive with those of RDX (Q = 5763 kJ kg-1, Dv = 8782 m s-1, and P = 34.7 GPa). Structural modification by using triazole and nitro-triazinane rings may be helpful in exploring more TNM derivatives and other types of high-performance explosives.

I2-DMSO-Mediated Transannulation of Benzo[d]isoxazol-3-amine: Direct Access to 2,4,5-Substituted Pyrimidine Derivatives.

An I2-DMSO-mediated multicomponent [3+1+2] cascade annulation reaction using aryl methyl ketones, enaminones, and benzo[d]isoxazol-3-amine as substrates has been developed. This metal-free reaction involved the transannulation of benzo[d]isoxazol-3-amines with the formation of two C-N bonds and a C-C bond in one pot. Notably, a pyrimidine ring with a 1,4-dicarbonyl scaffold could efficiently transform into a pyrimido[4,5-d]pyridazine skeleton. The phenolic hydroxyl group of the target product could undergo further modification with pharmaceuticals, demonstrating the utility of this method.

Triazole-induced planarization of a twisted tetrazole-based molecule towards energetic materials with improved thermostability and insensitivity.

Pursuing the structural planarization of energetic materials is an efficient method for achieving improved performance. Although many planar energetic molecules have been prepared so far, the innovation of advanced planar explosives still relies on the scientific intuition, experience and trial-and-error of researchers. Now, a triazole-induced planarization strategy is proposed based on the regulation of aromaticity, charge distribution, and hydrogen bonds. The incorporation of a triazole ring into the non-planar molecule 5-amino-1-nitriminotetrazole (VII) results in a planar energetic material named N-[5-amino-1-(1H-tetrazol-5-yl)-1H-1,2,4-triazol-3-yl]nitramide (3). Compared with VII (Td = 85 °C; IS < 0.25 J; FS < 5 N), 3 shows remarkably improved thermal stability (Td = 145 °C) and reduced sensitivities (IS = 20 J; FS > 360 N). The variation of thermal stability and mechanical sensitivity from VII to 3 reflects the effectiveness and superiority of the planarization strategy. Benefiting from the properties of 3, its energetic salt 5 exhibits excellent overall performance (Dv = 9342 m s-1; P = 31.6 GPa; Td = 201 °C; IS = 20 J; FS = 360 N), which is comparable to that of HMX. Moreover, the triazole-induced planarization strategy may serve as a guide for exploring advanced energetic materials.

N, S Co-Coordinated Zinc Single-Atom Catalysts for N-Alkylation of Aromatic Amines with Alcohols: The Role of S-Doping in the Reaction.

S-doping emerged as a promising approach to further improve the catalytic performance of carbon-based materials for organic synthesis. Herein, a facile and gram-scale strategy was developed using zeolitic imidazole frameworks (ZIFs) as a precursor for the fabrication of the ZIF-derived N, S co-doped carbon-supported zinc single-atom catalyst (CNS@Zn1-AA) via the pyrolysis of S-doped ZIF-8, which was modified by aniline, ammonia and thiourea and prepared by one-pot ball milling at room temperature. This catalyst, in which Zn is dispersed as the single atom, displays superior activity in N-alkylation via the hydrogen-borrowing strategy (120 °C, turnover frequency (TOF) up to 8.4 h-1). S-doping significantly enhanced the catalytic activity of CNS@Zn1-AA, as it increased the specific surface area and defects of this material and simultaneously increased the electron density of Zn sites in this catalyst. Furthermore, this catalyst had excellent stability and recyclability, and no obvious loss in activity after eight runs.

The design and synthesis of new advanced energetic materials based on pyrazole-triazole backbones.

A series of derivatives of the nitropyrazole-triazole backbone were designed through units' screening of 219 N-heterocycle compounds and were synthesized. Among them, the thermal stability of DNPAT (Tdec = 314 °C) is close to that of traditional heat-resistant explosive HNS (318 °C) while the detonation performance and sensitivity (D = 8889 m s-1; IS = 18 J) are better than those of HNS (D = 7612 m s-1; IS = 5 J) and traditional high-energy explosive RDX (D = 8795 m s-1; IS = 7.4 J), which is rarely reported in heat-resistant explosives. Moreover, compounds 4 and 6 show excellent performances (IS > 15 J, D > 9090 m s-1, P > 37.0 GPa), illustrating that compounds 4 and 6 may be used as secondary explosives. All these results enrich prospects for the development of energetic materials.

Site-Selective Oxidative Coupling Reaction of Diamines toward Aminoazo Compounds.

A selective oxidative coupling reaction of a diamine containing both C- and N-NH2 was achieved using acidic potassium permanganate as the coupling reagent. The reaction conditions were optimized, and the reaction selectivity was illustrated by quantum calculations. Furthermore, the azo-coupled product was derivatized to four nitroamine energetic materials with excellent detonation performances.

Dehydrogenative Syntheses of Biazoles via a "Pre-Join" Approach.

The structural motif of biazoles is the predominant substructure of many natural products, pharmaceuticals, and organic materials. Considerable efforts have focused on synthesizing these compounds; however, a limited number of processes have been reported for the efficient formation of biazoles. Herein, we report a "pre-join" approach for the dehydrogenative synthesis of biazoles, which are challenging to prepare using conventional methods. A bench-stable and easily synthesized pyrazine-based group is critical for this transformation. This strategy enables the homocoupling of biazoles and the heterocoupling of two different azoles. Due to the broad substrate scope, this strategy exhibits potential for use in other fields, such as medicine, materials, and natural product chemistry.

Effects of nitric acid concentration for nitration of fused [1,2,5]oxadiazolo[3,4-d]pyrimidine-5,7-diamine.

Nitration reactions are very often used for the selective synthesis of novel, high performing nitramine-based materials. Now nitration reactions of the fused 5,7-diamino pyrimidine derivative 1, under different nitric acid concentrations were examined. Concentrated nitric acid gave selectively N-(5-amino-4,5-dihydro-[1,2,5]oxadiazolo[3,4-d]pyrimidin-7-yl)nitramide, 2, while the fused ring nitrate salt, 4, and ring open nitrate salt, 3 were obtained using low concentrations of nitric acid (<70%). In addition, the cesium salt of the fused nitramine derivative 5 was synthesized. All new compounds were isolated in high yields and comprehensively characterized by NMR, FTIR spectroscopy, and elemental analyses. The molecular structures of 2, 3, and 5 were analyzed by single X-ray crystallographic data. These compounds have high calculated heats of formation and high crystal densities. Detonation properties for compounds 2 and 3 were calculated using EXPLO5 software. Fused ring compound 2 (vD, 8549 m s-1; P, 29.62 GPa), and nitrate salt, 3 (vD, 8392 m s-1; P, 29.37 GPa) have superior detonation properties compared with TNT (vD, 7303 m s-1; P, 21.30 GPa). In addition, electrostatic potentials, two-dimensional (2D)-fingerprints, and Hirshfeld surface analysis were used to predict the sensitive properties of compounds 2 and 3. The experimental sensitives suggest possible applications with insensitive energetic applications.

I2-DMSO Mediated Multicomponent [3+2] Annulation Reaction: An Approach to Pyrrolo[2,1-a]isoquinoline Derivatives with a Quaternary Center.

An I2-DMSO mediated multicomponent [3+2] cascade annulation reaction using methyl ketones, 1,2,3,4-tetrahydroisoquinolines (THIQ) and cyclopropenones as readily available substrates has been developed. This metal-free process involves N-H/α-C(sp3)-H trifunctionalization of THIQ and C-C bond cleavage of cyclopropenone, providing a direct approach to obtain pyrrolo[2,1-a]isoquinoline derivatives with a quaternary carbon center. Two C-C bonds and one C-N bond are formed efficiently in one pot.

Toward Advanced High-Performance Insensitive FOX-7-like Energetic Materials via Positional Isomerization.

For an energetic molecule with a definite elemental composition, the substituent type and position are the most important factors to influence its detonation performance and mechanical sensitivities. In this work, two pairs of FOX-7-like energetic isomers based on (2 and HTz-FOX; 5 and 6) were synthesized and characterized. Through positional isomerization, advanced high-performance insensitive explosives were obtained. Compounds 2 and 5 with an amino group adjacent to the electron-withdrawing side of the ethene bridge show both higher thermal stability and lower mechanical sensitivities (2: Td = 258 °C, impact sensitivity (IS) = 25 J, and friction sensitivity (FS) = 300 N; 5: Td = 264 °C, IS = 30 J, and FS = 320 N). In addition, 2 shows ultrahigh detonation performance (Dv = 9224 m s-1 and P = 31.1 GPa). These promising physicochemical properties are comparable to those of HMX (Dv = 9193 m s-1, P = 37.8 GPa, Td = 275 °C, IS = 7.4 J, and FS = 120 N), which suggests that 2 may be a promising energetic material in future applications.

An advanced primary explosive and secondary explosive based on a zwitterionic pyrazole-triazole derivative.

Two zwitterionic energetic materials containing a pyrazole-triazole backbone were synthesized and fully characterized. Compound 3 can serve as an ideal secondary explosive due to its high decomposition temperature (>200 °C), low impact sensitivity (>40 J), and excellent calculated detonation velocity (9090 m s-1). The good priming ability of compound 4 demonstrates that it is a potential candidate as a primary explosive, which was confirmed in the test. These results indicate that zwitterionic molecules are an efficient promising class for the future design of new high-energy density materials.

I2-DMSO-Mediated N-H/α-C(sp3)-H Difunctionalization of Tetrahydroisoquinoline: Formal [2 + 2 + 1] Annulation for the Construction of Pyrrolo[2,1-a]isoquinoline Derivatives.

An I2-DMSO-mediated cascade reaction using methyl ketones and 1,2,3,4-tetrahydroisoquinolines (THIQs) as commercially available substrates has been developed for the construction of pyrrolo[2,1-a]isoquinoline derivatives. This metal-free process involves N-H/α-C(sp3)-H difunctionalization of THIQ. Two C-C bonds and one C-N bond are formed in one pot under mild conditions. Besides, a quaternary carbon center has been constructed in this transformation efficiently.

From Nitro- to Heterocycle-Functionalized 1,2,4-Triazol-3-one Derivatives: Achieving High-Performance Insensitive Energetic Compounds.

5-Nitro-1,2,4-triazol-3-one, a nitro-functionalized 1,2,4-triazol-3-one (TO) derivative, shows excellent energetic properties and promising application potential. However, the use of the TO skeleton as an energetic material is still largely underexplored both theoretically and practically. We report here a mild and efficient method for obtaining the TO skeleton via a reaction of aminocarbohydrazide with BrCN. Two energetic compounds (2 and 5) were synthesized and fully characterized by 15N nuclear magnetic resonance, two-dimensional 1H-15N heteronuclear multiple-bond correlation, and single-crystal X-ray diffraction. The reaction mechanism was also studied with the aid of quantum calculations. Compound 2 shows promising properties as a high-performance insensitive energetic material.

Copper-Catalyzed Oxidative C(sp3)-H/C(sp3)-H Cross-Coupling Reaction of 3-Methylbenzo[c]isoxazoles with Methyl Ketones: Access to Indigoid Analogues.

A copper-catalyzed oxidative C(sp3)-H/C(sp3)-H cross-coupling reaction of methyl ketones and 3-methylbenzo[c]isoxazoles has been developed for the direct synthesis of 3-oxoindolin-2-ylidene derivatives. This process involves an intermolecular nucleophilic addition/ring-opening/aza-Michael addition cascade, providing indigoid analogues with high atom economy and as single isomers exclusively under mild conditions.

Energetic Tricyclic Polynitropyrazole and Its Salts: Proton-Locking Effect of Guanidium Cations.

An axisymmetric polynitro-pyrazole molecule, 3,5-di(3,5-dinitropyrazol-4-yl)]-4-nitro-1H-pyrazole (5), and its salts (6-12) were prepared and fully characterized. These compounds not only show promising energetic properties but also show a unique tautomeric switch via combining different cations with the axisymmetric compound (5). Its salts (6-9) remain axisymmetric when the cations are potassium, ammonium, or amino-1,2,4-triazolium. However, when the cations are guanidiums, the salts (10-12) dramatically become asymmetric owing to the fixed proton. The introduction of guanidium cations breaks the tautomeric equilibrium by blocking the prototropic transformations and results in the switch-off effect to tautomerism. The structural constraints of 1H NMR and 13C NMR spectra provide strong evidence for the unusual structural constraint phenomenon. These stabilized asymmetric tautomers are very important from the point of molecular recognition, and this research may promote further developments in synthetic and isolation methodologies for novel bioactive pyrazole-based compounds.

I2-DMSO mediated oxidative amidation of methyl ketones with anthranils for the synthesis of α-ketoamides.

An I2-DMSO mediated oxidative amidation of methyl ketones using anthranils as masked N-nucleophiles has been developed for the direct synthesis of α-ketoamides with high atom-economy. This metal-free process involves reductive N-O bond cleavage of anthranils and oxidative C-N bond formation of methyl ketones under mild conditions. The iodo group and electrophilic formyl group provide multiple possibilities for further functionalization of α-ketoamides.