Equilibration of 2H-azirine with vinylnitrene

Nishiwaki, Tarozaemon

doi:10.1039/c39720000565

Cited by 25 publications

(11 citation statements)

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“…Trapping with triphenylphosphine has suggested the existence of an equilibrium between 1-azirines and vinylnitrenes at 50–60 °C . Epimerization of azirine 25 on FVP at 400 °C (10 –5 hPa) suggests a thermal equilibrium between the azirine and the vinylnitrene in the gas phase.…”

Section: Azidesmentioning

confidence: 99%

Flash Vacuum Pyrolysis of Azides, Triazoles, and Tetrazoles

2017

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Flash vacuum pyrolysis (FVP) of azides is an extremely valuable method of generating nitrenes and studying their thermal rearrangements. The nitrenes can in many cases be isolated in low-temperature matrices and observed spectroscopically. NH and methyl, alkyl, aralkyl, vinyl, cyano, aryl and N-heteroaryl, acyl, carbamoyl, alkoxycarbonyl, imidoyl, boryl, silyl, phosphonyl, and sulfonyl nitrenes are included. FVP of triazoloazines generates diazomethylazines and azinylcarbenes, which often rearrange to the energetically more stable arylnitrenes. N elimination from monocyclic 1,2,3-triazoles can generate iminocarbenes, 1H-azirines, ketenimines, and cyclization products, and 1,2,4-triazoles are precursors of nitrile ylides. Benzotriazoles are preparatively useful precursors of cyanocyclopentadienes, carbazoles, and aza-analogues. FVP of 5-aryltetrazoles can result in double N elimination with formation of arylcarbenes or of heteroarylcarbenes, which again rearrange to arylnitrenes. Many 5-substituted and 2,5-disubstituted tetrazoles are excellent precursors of nitrile imines (propargylic, allenic, or carbenic), which are isolable at low temperatures in some cases (e.g., aryl- and silylnitrile imines) or rearrange to carbodiimides. 1,5-Disubstituted tetrazoles are precursors of imidoylnitrenes, which also rearrange to carbodiimides or add intramolecularly to aryl substituents to yield indazoles and related compounds. Where relevant for the mechanistic understanding, pyrolysis under flow conditions or in solution or the solid state will be mentioned. Results of photolysis reactions and computational chemistry complementing the FVP results will also be mentioned in several places.

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Section: Azidesmentioning

confidence: 99%

Flash Vacuum Pyrolysis of Azides, Triazoles, and Tetrazoles

2017

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“…To describe equilibrium structures of 2-formyl-2H-azirine in low-lying electronic states, one needs the π and π * orbitals of both C= =N and C= =O groups, the σ and σ * orbitals of both C-C and C-N single bonds in the azirine ring, and the nonbonding orbitals of the nitrogen and oxygen atoms, that is, 12 electrons in ten orbitals, referred to as CAS (12,10) hereafter. For isoxazole, a CAS(12,10) active space, including the π and π * orbitals of both C= =N and C= =C groups, the σ and σ * orbitals of both C-C and N-O bonds, and the nonbonding orbitals of the nitrogen and oxygen atoms, was also used in the equilibrium structure optimizations.…”

Section: A Electronic Structure Calculationsmentioning

confidence: 99%

“…In addition, ab initio based dynamics simulations were performed at the SA2-CAS (12,10) or SA3-CAS(12,10) level of theory. A comparison with the CASPT2 calculations with the (12,10) active space is given in Table S2 of the supplementary material 86 for all CASSCF optimized geometries, which provides an evaluation of the accuracy of the CASSCF calculations.…”

Section: A Electronic Structure Calculationsmentioning

confidence: 99%

“…11 The thermal and photochemical reactions of 2H-azirines have been studied extensively. Pyrolysis of 2Hazirines usually gives products derived from the C-N single bond cleavage of the azirine ring, [12][13][14] whereas photoexcitation of 2H-azirines leads most frequently to the C-C single bond cleavage of the azirine ring, yielding the corresponding nitrile ylides. [15][16][17][18][19][20] However, photochemical cleavage of the C-N single bond was observed in some 2H-azirine derivatives that have an electron-withdrawing substitution at the C 2 atom of the azirine ring.…”

Section: Introductionmentioning

confidence: 99%

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Photoinduced reactions of both 2-formyl-2H-azirine and isoxazole: A theoretical study based on electronic structure calculations and nonadiabatic dynamics simulations

Cao

2015

The Journal of Chemical Physics

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In the present work, the combined electronic structure calculations and dynamics simulations have been performed to explore photocleavages of 2-formyl-2H-azirine and isoxazole in the gas phase and the subsequent rearrangement reactions. The carbonyl n → π(*) transition induces a cleavage of the C-N single bond of 2-formyl-2H-azirine to yield β-formylvinylnitrene in open-shell singlet state. However, the n → π(*) excitation of the imine chromophore results in a cleavage of the C-C single bond, producing a nitrile ylide intermediate through an internal conversion to the ground state. β-formylvinylnitrene and nitrile ylide with the carbonyl group are easily transformed into 2-formyl-2H-azirine and oxazole, respectively. The N-O bond cleavages on both S1((1)ππ(*)) and S2((1)nNπ(*)) of isoxazole are ultrafast processes, and they give products of 2-formyl-2H-azirine, 3-formylketenimine, HCN + CHCHO, and HCO + CHCHN. Both 2H-azirines and ketenimines were suggested to be formed from the triplet vinylnitrenes by intersystem crossing in the previous studies. However, our calculations show that the singlet β-formylvinylnitrene is responsible for the formation of 2-formyl-2H-azirine and 3-formylketenimine, and the singlet vinylnitrenes can play a key role in the photoinduced reactions of both 2H-azirines and isoxazoles.

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“…Evidence for the existence of this intermediate comes from the thermal ring opening of 2,3-diaryl-2-cyano-2H-azirine where the vinylnitrene was trapped with phosphanes [4]. On the other hand, it was known that heating a solution of 3-phenyl-2H-azirine-2-carboxaldehyde (5a) at 200°C leads to 3-phenylisoxazole (6a) in high yield [5a].…”

Section: Introductionmentioning

confidence: 99%

4-Halo-1,3-oxazoles: Unambiguous structural assignment of 2-halo-2-benzoyl-2H-azirine-3-carboxylates thermal ring expansion products

Lopes

Nunes

Fausto

et al. 2009

Journal of Molecular Structure

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a b s t r a c t IR spectroscopy in cryogenic argon matrix of methyl 4-chloro-5-phenyl-1,3-oxazole-2-carboxylate and methyl 4-chloro-5-phenylisoxazole-3-carboxylate was applied for the structural assignment of these isomeric heterocycles. It was demonstrated that methyl 2-benzoyl-2-halo-2H-azirine-3-carboxylates undergo thermal ring expansion to give 4-halo-5-phenyl-1,3-oxazole-2-carboxylates and not the isomeric isoxazoles.

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Equilibration of 2H-azirine with vinylnitrene

Abstract: Treatment of 2,3-diaryl-2H-azirine-2-carboxamide with triphenylphosphine and carbon tetrachloride affords the triphenyliminophosphorane (4).

Cited by 25 publications

References 0 publications

Flash Vacuum Pyrolysis of Azides, Triazoles, and Tetrazoles

Flash Vacuum Pyrolysis of Azides, Triazoles, and Tetrazoles

Photoinduced reactions of both 2-formyl-2H-azirine and isoxazole: A theoretical study based on electronic structure calculations and nonadiabatic dynamics simulations

4-Halo-1,3-oxazoles: Unambiguous structural assignment of 2-halo-2-benzoyl-2H-azirine-3-carboxylates thermal ring expansion products

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