Formal C-H insertion of diketocarbene generated by rhodium(II)-catalyzed decomposition of diazodimedone into a benzene molecule

Diketocarbene generated by rhodium(II) acetate-catalyzed decomposition of diazodimedone reacts with benzene at room temperature to give 5,5-dimetlryl-2-phenylcyclohexane-1,3-dione in 88% yield.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 491–493, February, 1996     

Synthesis, Thermolysis, and Mass Spectrometry of Perfluorinated Di- and Triazidopyridines

2,4-Diazido-3,5,6-trifluoropyridine and 2,4,6-triazido-3,5-difluoropyridine were obtained by the reaction of pentafluoropyridine with sodium azide in aqueous acetone. Under the action of electron impact the 2,4-diazidopyridine undergoes sequential fission of the azide groups in positions 2 and 4 of the pyridine ring and ring contraction with the formation of a characteristic [M-2N₂-F]⁺ ion. On the other hand thermolysis of the same diazide is accompanied by the selective decomposition of its -azide group with the formation of 4-amino-2-azido-3,5,6-trifluoropyridine. The effect of selective decomposition of the azide groups in 2,4-diazidopyridines on thermolysis and under electron impact is caused by the different distribution of bonding orbital density at the - and -azide groups respectively in the initial diazide and its radical cation. One of the routes of the triazide decomposition under electron impact is the form! ation of the [M-N₂2]⁺ ion due to decomposition of the -azide group.     

Synthesis of 7-arylmethyl-substituted derivatives of 2-amino-2-pyrrolydin-1-yl-5,6,7,8-tetrahydropyrido-[3,4-<Emphasis Type="Italic">d</Emphasis>]pyrimidine

7-Benzyl-2-pyrrolidin-1-yl-5,6,7,8-tetrahydro-3H-pyrido[3,4-d]pyrimidin-4-one was prepared by condensation of 1-benzyl-4-ethoxycarbonyl-3-oxopiperidine with pyrrolidine-1-carboxamidine. Subsequent treatment of the product with trifluoromethansulfonyl anhydride, aqueous ammonia, and hydrogen in the presence of palladium on carbon gave 4-amino-2-pyrrolidin-1-yl-5,6,7,8-tetrahydropyrido[3,4-d]pyrimidine in 80% yield. The given compound was used in the reductive amination of aldehydes in the synthesis of various 7-arylmethyl-substituted derivatives of 4-amino-2-pyrrolidin-1-yl-5,6,7,8-tetrahydropyrido[3,4-d]pyrimidine. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, 1374–1381, September, 2007.     

EPR spectroscopy of quintet 4-amino-3,5-dichloropyridine-2,6-diyldinitrene isolated in solid argon

An EPR spectrum of solid Ar isolated quintet 4-amino-3,5-dichloropyridin-2,6-diyldinitrene that formed by the photolysis of 4-amino-2,6-diazido-3,5-dichloropyridine at 15 K was recorded. Using computer simulation based on numerical diagonalization of the quintet spin Hamiltonian matrices, it was established that this EPR spectrum corresponds to a quintet spin state with the magnetic parameters g = 2.0023, |D _q| = 0.2100 cm⁻¹, and |E _q| = 0.0560 cm⁻¹. Owing to high resolution of the experimental spectrum, the zero-field splitting parameters of the quintet intermediate were determined to an accuracy of at least 5·10⁻⁴ cm⁻¹. Calculations of the fine-structure energy levels in external magnetic field and the dependences of the EPR signal positions and intensities of the quintet dinitrene on the direction of external magnetic field were performed for the first time. This allowed unambiguous assignment of all EPR lines of quintet molecules having both in-principal-axis and off-principal-axis orientations. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2284–2289, December, 2007.     

Synthesis and regioselective cycloaddition reaction of 2,4,6-triazido-3-chloro-5-cyanopyridine with norbornene

Treatment of 3-cyanotetrachloropyridine with sodium azide gives 2,4,6-triazido-3-chloro-5-cyanopyridine. This compound reacts regioselectively with norbomene to form an aziridinyl cydoadduct only at the azido group in position 4 of the pyridine ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1650–1652, December, 1993.     

Thermal decomposition of 2,4,6-triazido-1,3,5-triazine

The thermal decomposition of 2,4,6-triazido-1,3,5-triazine in the melt and a dinonyl phthalate solution is studied by thermogravimetry, manometry, mass spectrometry, and IR spectroscopy. The kinetic and activation parameters of the process are determined. The only gaseous product of the reaction is nitrogen. This fact, along with the structure of the condensed residue formed during the thermal decomposition of 2,4,6-triazido-1,3,5-triazine in the melt, are indicative of the abstraction of a nitrogen molecule from an azide group at the initial stage and of the subsequent reactions leading to the formation of a planar network of polyconjugated bonds between C and N atoms. For the thermal decomposition of 2,4,6-triazido-1,3,5-triazine in solution the preexponential factor and activation energy are found to be 10^12.8 s^–1 and 34100 cal/mol, respectively, which are characteristic of the thermal decomposition of most azides. To explain why these parameters are substantially higher for the reaction in the melt (10^17.4 s^–1 and 42300 cal/mol), it is assumed that, in this case, the process proceeds by the polymerization (polycondensation) mechanism to form twodimensional networks, with the apparent kinetic parameters being effective quantities. Based on these data, it is concluded that the high sensitivity of 2,4,6-triazido-1,3,5-triazine to external influences is of kinetic nature.     

Thermal decomposition of 2,4,6-triazidopyridine

The thermal decomposition of 2,4,6-triazidopyridine in the melt is studied using thermogravimetry, manometry, mass spectrometry, and IR spectroscopy. In the temperature range of 120–160°C, the process obeys the first-order kinetic law, being described by the Arrhenius equation k [s^–1] = 10^{12.8 ± 0.4}exp[–(31200 ± 1500)]/RT with values of the parameters typical of the thermal decomposition of aromatic and heterocyclic azides. The reaction produces nitrogen, as the only gaseous product. Unlike the other heterocyclic azides, the decomposition of which is characterized by anomalously high values of the Arrhenius parameters, the thermal decomposition of 2,4,6-triazidopyridine yields a condensed product having a system of polyconjugated bonds with higher force characteristics. It is concluded that the decomposition of 2,4,6-triazidopyridine proceeds by a mechanism in which the rate-limiting step is the dissociation of the nitrogen molecule from the azide group to form a nitrene.     

The properties of quintet dinitrenes in 2,4,6-triazido-3,5-dichloropyridine crystals

The gamma radiolysis of crystalline 2,4,6-triazido-3,5-dichloropyridine (TACP) was studied by the EPR method. The molecular and crystal structure of TACP was determined by X-ray structure analysis. The prolonged radiolysis of TACP at 77 K caused the appearance of characteristic EPR signals of quintet 2,6-dinitreno-4-azido-3,5-dichloropyridine (2,6-DN) and 2,4-dinitreno-6-azido-3,5-dichloropyridine (2,4-DN). The predominant decomposition of the α-azide groups of TACP was explained by the special features of its molecular and crystal structure. The saturation of the EPR signals of quintet 2,6-DN and 2,4-DN and one-electron radicals with S = 1/2 as the microwave field power increased was studied. The quintet dinitrenes were found to be thermally unstable; they remained in TACP crystals up to 245–250 K.     

Magnetic anisotropy parameters of matrix-isolated septet 1,3,5-trinitreno-2,4,6-trichlorobenzene

An ESR spectrum of high-symmetry septet 1,3,5-trinitreno-2,4,6-trichlorobenzene generated under photolysis of 1,3,5-triazido-2,4,6-trichlorobenzene in solid argon at 15 K was recorded. Computer simulation revealed that the spectrum corresponds to the septet spin state with the fine structure parameters D _S = ?0.0957±0.0006 cm^?1 and E _S = 0±0.0004 cm^?1. These values of the magnetic anisotropy parameters D _S and E _S are in good agreement with the results of UDFT calculations. The spin-spin (D _SS) and spin-orbit (D _SO) coupling parameters of septet molecules with D _3h symmetry are negative and mutually enhance the magnetic anisotropy of these molecules. The contribution of the spin-orbit coupling to the magnetic anisotropy of 1,3,5-trinitreno-2,4,6-trichlorobenzene is higher than 11% due to the presence of three chlorine atoms in the molecule. This suggests the possibility of further strengthening the magnetic properties of septet 1,3,5-trinitrenobenzenes by introducing bromine and iodine atoms into positions 2, 4, and 6 of their benzene rings.