Isolation of diazacycloheptatetraenes from thermal nitrene-nitrene rearrangements

Wentrup, Curt; Winter, Hans

doi:10.1021/ja00539a039

Cited by 112 publications

(58 citation statements)

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“…The azide forms cannot be detected in solution at room temperature but are readily formed on mild FVT at 100-2008C and isolated at low temperatures. [53] The azide cyclizes back to the tetrazole at ,-108C. FVT of the tetrazole/azide mixture at 370-5008C causes decomposition to the open-shell singlet S 1 2-pyridylnitrene 53 (Scheme 8).…”

Section: -Pyridylnitrene ] 2-and 4-pyrimidinylcarbenes ] Cyanopyrrolesmentioning

confidence: 99%

Chemical Activation in Azide and Nitrene Chemistry: Methyl Azide, Phenyl Azide, Naphthyl Azides, Pyridyl Azides, Benzotriazoles, and Triazolopyridines

Wentrup¹

2013

Aust. J. Chem.

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Chemical activation (the formation of 'hot' molecules due to chemical reactions) is ubiquitous in flash vacuum thermolysis (FVT) reactions, and awareness of this phenomenon is indispensable when designing synthetically useful gas-phase reactions. Chemical activation is particularly prevalent in azide chemistry because the interesting singlet nitrenes are high-energy intermediates, and their reactions are highly exothermic. Consequently, chemical activation is observed in the isomerization of methylnitrene CH 3 N to methylenimine (methanimine) CH 2 ¼NH, facilitating the elimination of hydrogen to form HCN or HNC. Rearrangements of phenylnitrene, 1-and 2-naphthylnitrenes, and 2-, 3-and 4-pyridylnitrenes afford cyanocyclopentadiene, 3-and 2-cyanoindenes, and 2-and 3-cyanopyrroles, all showing the effects of chemical activation by undergoing facile interconversion of isomers. Chemical activation can often be reduced or removed entirely by increasing the pressure, thereby promoting collisional deactivation. Larger molecules having more degrees of freedom are better able to dissipate excess energy; therefore the effects of chemical activation are less pronounced or completely absent in the formation of 3-cyanoindole and 1-cyanobenzimidazoles from 3-and 4-quinolylnitrenes and 4-quinazolinylnitrenes, respectively. In compounds possessing nitro groups, chemical activation can cause the loss of the nitro group at nominal temperatures far below those normally needed to cleave the C-NO 2 bond.

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Section: -Pyridylnitrene ] 2-and 4-pyrimidinylcarbenes ] Cyanopyrrolesmentioning

confidence: 99%

Chemical Activation in Azide and Nitrene Chemistry: Methyl Azide, Phenyl Azide, Naphthyl Azides, Pyridyl Azides, Benzotriazoles, and Triazolopyridines

Wentrup¹

2013

Aust. J. Chem.

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“…This inconsistency can be explained by taking into account the fact that calculations were carried out on isolated molecules in the gas phase with no solvent effects included. As is known from the work of Wentrup and co-workers 5,10,17 and from other theoretical calculations, 19,20 the azido form is much more stable than the tetrazole form in the gas phase. Differences in calculated SCF energies for both the azide and tetrazole forms are helpful in studying this type of equilibrium.…”

Section: Resultsmentioning

confidence: 82%

“…À1 increase in intensity and can be assigned to the azido form. 10 The IR spectra in the solid state and in solutions are useful but only for qualitative estimation. To characterize fully the type of equilibria considered, NMR methods are irreplaceable.…”

Section: Resultsmentioning

confidence: 99%

1H,13C and15N NMR and IR studies of halogen-substituted tetrazolo[1,5-a]pyridines

Cmoch

Korczak

Stefaniak

et al. 1999

J. Phys. Org. Chem.

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The tetrazole-azide tautomerization of some halogen-substituted tetrazolo [1,5-a] N NMR spectroscopy at various temperatures. The tetrazolopyridines can exhibit equilibrium between the azide and the tetrazole forms. For some of them slow exchange occurs on the NMR time-scale, such that it is possible to estimate equilibrium constants. The position and nature of the substituent in the pyridine ring result in stabilization or destabilization of the tetrazole form and exert a strong influence on the values found for the equilibrium constants. A saturation transfer experiment was carried out for 5-bromotetrazolo[1,5-a]pyridine and the rate constants were estimated. Moreover, based on the van't Hoff equation, the enthalpy DH°and entropy DS°for the tautomerization were calculated. Ab initio calculated energies and charge distribution are in good agreement with differences observed in the tetrazole-azide equilibrium constants.

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“…The cyclic carbodiimide 115, obtained from tetrazolophenanthridine 114, is relatively long-lived, being easily isolable below Ϫ100°C and dimerizing in high yield to the diazete derivative 116 at ca Ϫ45°C; the structure of 114 has been proved by X-ray crystallography, [75] and it has been synthesized and analyzed a second time using a different type of precursor (Scheme 16) [76] .…”

Section: Carbodiimides From Tetrazolesmentioning

confidence: 99%

Formation of Cumulenes, Triple-Bonded, and Related Compounds by Flash Vacuum Thermolysis of Five-Membered Heterocycles

Yranzo¹,

Elguero²,

Flammang³

et al. 2001

Eur. J. Org. Chem.

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Isolation of diazacycloheptatetraenes from thermal nitrene-nitrene rearrangements

Cited by 112 publications

References 0 publications

Chemical Activation in Azide and Nitrene Chemistry: Methyl Azide, Phenyl Azide, Naphthyl Azides, Pyridyl Azides, Benzotriazoles, and Triazolopyridines

Chemical Activation in Azide and Nitrene Chemistry: Methyl Azide, Phenyl Azide, Naphthyl Azides, Pyridyl Azides, Benzotriazoles, and Triazolopyridines

1H,13C and15N NMR and IR studies of halogen-substituted tetrazolo[1,5-a]pyridines

Formation of Cumulenes, Triple-Bonded, and Related Compounds by Flash Vacuum Thermolysis of Five-Membered Heterocycles

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