Flash Vacuum Pyrolysis of Isoxazoles, Pyrazoles and Related Compounds

Yranzo, Gloria I.; Moyano, Elizabeth L.

doi:10.2174/1385272043370113

Cited by 22 publications

(21 citation statements)

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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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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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“…[16] There are no previous mechanistic studies on the gasphase dehydrogenation of benzylimidazolidinones. Therefore, it became very important to acknowledge that precursor 3 can be present in tautomeric equilibrium and, therefore, the mechanism would strongly depend on which tautomer is reacting.…”

Section: Resultsmentioning

confidence: 99%

“…In addition, this kind of mechanistic information can be better retrieved through the use of FVP techniques to obtain kinetic and thermodynamic parameters. [16] There are no previous mechanistic studies on the gasphase dehydrogenation of benzylimidazolidinones. We suggest two main ways of analyzing the mechanism: a stepwise manner via a radical intermediate (Scheme 2, paths A and B) and a concerted route (Scheme 2, paths C-F).…”

Section: Resultsmentioning

confidence: 99%

Highly Efficient Dehydrogenation of 5‐Benzyl‐3‐phenyl‐2‐thioxoimidazolidin‐4‐one: Microwave versus Flash Vacuum Pyrolysis Conditions

et al. 2012

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5‐Benzyl‐3‐phenyl‐2‐thioxoimidazolidin‐4‐one underwent thermal dehydrogenation to afford 5‐benzylidene‐2‐thioxoimidaxolidin‐4‐one under microwave and flash vacuum pyrolysis conditions. A high predominance of the Z‐isomer over the E‐isomer of the imidazolidinone product was achieved. By using DFT and NBO calculations, the mechanism of the dehydrogenation and the selectivity were also explored.

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“…The 2H-azirines can also undergo ring cleavage to give nitrile ylides 187 followed by recyclization to give oxazoles 189 as the final product. However, thermolysis of isoxazoles unsubstituted at C3 usually leads to nitriles 188 (Scheme 9.75) [284,285]. Thermolysis of 3-unsubstituted 1,2-benzisoxazoles yields the corresponding salicylnitriles 190 [286].…”

Section: 2-benzisothiazolesmentioning

confidence: 99%