Gas-phase thermal isomerization of some aminomethylisoxazoles

Perez, J. D.; DIAZ, R. G. DE; Yranzo, Gloria I.

doi:10.1021/jo00330a025

Cited by 33 publications

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“…2 H -Azirines are strained unsaturated heterocyclic compounds possessing a CN double bond within a three-membered ring. The chemistry of 2 H -azirines has thrived over the past few decades, and these compounds have been utilized for the construction of various heterocyclic compounds. , In particular, 2-acyl-3-alkyl-2 H -azirines ( 2a ) are key intermediates in the transformation of isoxazoles ( 1a ) to oxazoles ( 3a ) , − and they can be directly transformed into oxazoles under photoirradiation (Figure a) . As shown in Figure b, the intermediacy of a nitrile ylide, formed through C–C bond cleavage, in this transformation was proposed on the basis of observation of the infrared (IR) spectra in an argon matrix at 15K .…”

Section: Introductionmentioning

confidence: 99%

Base-Induced Transformation of 2-Acyl-3-alkyl-2H-azirines to Oxazoles: Involvement of Deprotonation-Initiated Pathways

2017

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An experimental study of base-induced transformation reaction of 2-acyl-3-alkyl-2H-azirines to oxazoles indicated that a deprotonation-initiated mechanism is involved, in addition to nucleophilic addition to the imine functionality. Calculations suggested the participation of a ketenimine (ethenimine) intermediate generated by azirine ring opening of the carbanion intermediate formed by α-deprotonation of 2H-azirine. The ketenimine intermediate possessing methyl substituents at C(3) appears to be more stable than the tautomeric nitrile ylide which was proposed to be involved in photoinduced and pyrolysis reactions of 2-acyl-3-alkyl-2H-azirines to afford oxazoles. Thus, intermediacy of ketenimine is consistent with both experimental and computational results, at least under strongly basic reaction conditions.

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Section: Introductionmentioning

confidence: 99%

Base-Induced Transformation of 2-Acyl-3-alkyl-2H-azirines to Oxazoles: Involvement of Deprotonation-Initiated Pathways

2017

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“…[27][28][29] The thermal decomposition of isoxazoles has been studied under different conditions, and many products, such as nitriles, 2H-azirines, and oxazoles, were observed in previous experimental studies. [30][31][32][33][34][35][36][37][38][39][40][41][42] Recently, Nunes et al 43 revisited the pyrolysis of parent isoxazole and its 5-methyl and 3,5dimethyl derivatives in argon matrices by the high-pressure pulsed pyrolysis method. Ketenimine and carbon monoxide were observed to be the primary products.…”

Section: Introductionmentioning

confidence: 99%

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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“…In contrast, 1c formed the previously identified products, azirine 3c and oxazole 5c. 8 Concurrently, we engaged in quantum chemical calculations to simulate and assign the observed IR spectra and to model the potential surfaces on which the observed rearrangements take place. We paid particular attention to the possible involvement of the elusive yet pivotal vinylnitrene 2, which is known to have a triplet ground state and whose lowest singlet state is of open-shell nature.…”

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The Pyrolysis of Isoxazole Revisited: A New Primary Product and the Pivotal Role of the Vinylnitrene. A Low-Temperature Matrix Isolation and Computational Study

et al. 2011

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This paper describes the pyrolysis of parent isoxazole and of its 5-methyl and 3,5-dimethyl derivatives by the high-pressure pulsed pyrolysis method, where activation of the precursor molecules occurs predominantly by collisions with the host gas (Ar in our case), rather than with the walls of the pyrolysis tube, where catalyzed processes may occur. The products were trapped at 15 K in Ar matrices and were characterized by vibrational spectroscopy. Thereby, hitherto unobserved primary products of pyrolysis of isoxazole and of its 5-methyl derivative, 3-hydroxypropenenitrile or 3-hydroxybutenenitrile, respectively, were observed. E-Z photoisomerization could be induced in the above hydroxynitriles. On pyrolysis of isoxazole, ketenimine and CO were observed as decomposition products, but this process did not occur when the 5-methyl derivative was pyrolyzed. Instead, the corresponding ketonitrile was formed. In the case of 3,5-dimethylisoxazole, 2-acetyl-3-methyl-2H-azirine was detected at moderate pyrolysis temperatures, whereas at higher temperatures, 2,5-dimethyloxazole was the only observed rearrangement product (next to products of dissociation). These findings are rationalized on the basis of quantum chemical calculations. Thereby it becomes evident that carbonyl-vinylnitrenes play a pivotal role in the observed rearrangements, a role that had not been recognized in previous theoretical studies because it had been assumed that vinylnitrenes are closed-shell singlet species, whereas they are in fact open-shell singlet biradicaloids. Thus, the primary processes had to be modeled by the multiconfigurational CASSCF method, followed by single-point MR-CISD calculations. The picture that emerges from these calculations is in excellent accord with the experimental findings; that is, they explain why some possible products are observed while others are not.

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Gas-phase thermal isomerization of some aminomethylisoxazoles

Abstract: Scheme III concentrated, and a chromatographic separation under the same conditions as above gave 4b: 75% yield; mp 229-230 °C; mass spectrum, m/e 438; NMR (CDClg) 6.67-6.92 (s, 4 H), 5.7 (d, 1

Cited by 33 publications

References 1 publication

Base-Induced Transformation of 2-Acyl-3-alkyl-2H-azirines to Oxazoles: Involvement of Deprotonation-Initiated Pathways

Base-Induced Transformation of 2-Acyl-3-alkyl-2H-azirines to Oxazoles: Involvement of Deprotonation-Initiated Pathways

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

The Pyrolysis of Isoxazole Revisited: A New Primary Product and the Pivotal Role of the Vinylnitrene. A Low-Temperature Matrix Isolation and Computational Study

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