A systematic study of the inverse electron demand Diels–Alder reactions of 1,2,3-triazines is disclosed, including an examination of the impact of a C5 substituent. Such substituents were found to exhibit a remarkable impact on the cycloaddition reactivity of the 1,2,3-triazine without altering, and perhaps even enhancing, the intrinsic cycloaddition regioselectivity. The study revealed not only that the reactivity may be predictably modulated by a C5 substituent (R = CO2Me > Ph > H) but also that the impact is of a magnitude to convert 1,2,3-triazine (1) and its modest cycloaddition scope into a heterocyclic azadiene system with a reaction scope that portends extensive synthetic utility, expanding the range of participating dienophiles. Significantly, the studies define a now powerful additional heterocyclic azadiene, complementary to the isomeric 1,2,4-triazines and 1,3,5-triazines, capable of dependable participation in inverse electron demand Diels–Alder reactions, extending the number of complementar...

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Inverse electron demand Diels-Alder reactions of 1,2,3-triazines: pronounced substituent effects on reactivity and cycloaddition scope.

3.01 – Pyrazoles

Reaction of the dinuclear M(II)-bis(mu-hydroxo) complexes of nickel and cobalt, [(M(II)(TpR)]2(mu-OH)2] (M = Ni; 3Ni M = Co: 3Co), with one equivalent of H2O2 yields the corresponding M(III)-bis(mu-oxo) complexes, [[M(III)(TpR)]2-(mu-O)2] (M=Ni; 2Ni, M=Co: 2Co). The employment of a series of TpMe2,X (TpMe2,X = hydrotris(3,5-dimethyl-4-X-1-pyrazolyl)borate; X = Me, H, Br) as a metal supporting ligand makes it possible to isolate and structurally characterize the thermally unstable M(III)-bis-(mu-oxo) complexes 2Ni and 2Co. Both the starting (3Ni and 3Co) and resulting complexes (2Ni and 2Co) contain five-coordinate metal centers with a slightly distorted square-pyramidal geometry. Characteristic features of the nickel complexes 2Ni, such as the two intense absorptions around 400 and 300 nm in the UV-visible spectra and the apparent diamagnetism, are very similar to those of the previously reported bis(mu-oxo) species of Cu(III) and Ni(III) with ligands other than TpR, whereas the spectroscopic properties of the cobalt complexes 2Co (i.e., paramagnetically shifted NMR signals and a single intense absorption appearing at 350 nm) are clearly distinct from those of the isostructural nickel compounds 2Ni. Thermal decomposition of 2Ni and 2Co results in oxidation of the inner saturated hydrocarbyl substituents of the TpR ligand. Large kH/kD values obtained from the first-order decomposition rates of the TpMe3 and Tp(CD3)2,Me derivatives of 2 evidently indicate that the rate-determining step is an hydrogen abstraction from the primary C-H bond of the methyl substituents. mediated by the M(III)2-(mu-O)2 species. The nickel complex 2Ni shows reactivity about 10(3) times greater than that of the cobalt analogue 2Co. The oxidation ability of the M(III)(mu-O)2M(III) core should be affected by the hindered TpR ligand system, which can stabilize the +2 oxidation state of the metal centers.

Structural Characterization and Intramolecular Aliphatic C−H Oxidation Ability of MIII(μ-O)2MIII Complexes of Ni and Co with the Hydrotris(3,5-dialkyl-4-X-pyrazolyl)borate Ligands Tp (X=Me, H, Br) and Tp

The unique and facile synthesis of 7-nitro-4-oxo-4,8-dihydro-[1,2,4]triazolo[5,1-d][1,2,3,5]tetrazine 2-oxide (HBCM) and a proposed mechanism for its formation are described. The hygroscopicity of HBCM was overcome by transforming it into salts. The energetic salts of HBCM were characterized by 1H and 13C nuclear magnetic resonance spectroscopy, infrared spectroscopy, differential scanning calorimetry (DSC) and elemental analysis. The crystal structures of the sodium and guanidinium salts were determined by single-crystal X-ray diffraction. The densities of the salts ranged from 1.77 to 1.97 g cm−3. Most of the energetic salts decomposed above 230 °C and tended to be insensitive to impact, friction and electrostatic discharge. Theoretical performance calculations (Gaussian 03 and EXPLO5) for the energetic salts provide detonation pressures and velocities within the ranges of 25.2 to 39.5 GPa and 7856 to 9069 m s−1, respectively. The hydroxylammonium salt showed high density (1.97 g cm−3), acceptable decomposition temperature (Td = 197 °C), low sensitivities, and excellent detonation velocity (9069 m s−1) and pressure (39.5 GPa), which suggests that it has the potential to be used as a high-energy-density material.

The unique synthesis and energetic properties of a novel fused heterocycle: 7-nitro-4-oxo-4,8-dihydro-[1,2,4]triazolo[5,1-d][1,2,3,5]tetrazine 2-oxide and its energetic salts

A mild and efficient method for the regioselective iodination of pyrazoles

Reactions of N-aminopyrazoles with halogenating reagents (Cl2, Br2, I2, BrCl, ICl, IBr, N-chlorosuccinimide, and N-bromosuccinimide) were examined. Some of these reagents preferentially lead to oxidation of the amino group to give the corresponding 1, 2, 3-triazines as major products, while others mainly gave either or both of 1-amino-4-halopyrazoles and 5-halo-1, 2, 3-triazines as the result of halogenation of the 4-position of the pyrazole ring prior to the oxidation of the amino group. In some cases, the oxidation of the amino group and the halogenation of the pyrazole ring proceeded concurrently to form not only the unhalogenated triazines but also the l -amino-4-halopyrazoles and the 5-halotriazines. Various reagents and reaction conditions were explored to utilize the reaction for the synthesis of halogenated and unhalogenated 1, 2, 3-triazines.

Reactions of N -Aminopyrazoles with Halogenating Reagents and Synthesis of 1, 2, 3-Triazines

The reactivity of unsubstituted 1,2,3-triazine was investigated using various nucleophilic and electrophilic reagents, molecular orbital calculations, and low temperature nmr measurements

The reactivity of monocyclic 1,2,3-triazine

The N-oxidation products of 4, 5, 6-triaryl-1, 2, 3-triazines were decided to be the 2-oxides on the basis of spectral data and X-ray crystallography; the structures are different from those reported previously.

Revised Structure of N-Oxidation Products of 4,5,6-Triaryltriazines: 1,2,3-Triazine 2-Oxides.

Halo-1, 2, 3-triazines (1 and 3) were synthesized by treating 1-aminopyrazoles (2) with chlorine and bromine, without isolating intermediary triazines or halogenated 1-aminopyrazoles.

A facile synthesis of halo-1, 2, 3-triazines

I): l'amino-1 phenyl-3 pyrazole, C 9 H 9 N 3 , cristallise dans P2 1 /n avec a=18,729, b=5,742 et c=15,807 A, β=104,39 o , Z=8; affinement jusqu'a R=0,053. II: l'amino-1 methyl-5 phenyl-3 pyrazole, C 10 H 11 N 3 , cristallise dans Pcab avec a=10,945, b=21,535 et c=57,619 A, Z=8; affinement jusqu'a R=0,060. L'azote amino a le caractere sp 3 dans les deux cas

C. Kawabata

Papers

Reactions of N -Aminopyrazoles with Halogenating Reagents and Synthesis of 1, 2, 3-Triazines

The reactivity of monocyclic 1,2,3-triazine

Revised Structure of N-Oxidation Products of 4,5,6-Triaryltriazines: 1,2,3-Triazine 2-Oxides.

A facile synthesis of halo-1, 2, 3-triazines

Structures of aminopyrazole derivatives