23012-11-5Relevant articles and documents
Gas-Phase Thermal Isomerization of Some Aminomethylisoxazoles
Perez, Jorge D.,Diaz, Rosario G. de,Yranzo, Gloria I.
, p. 3505 - 3508 (1981)
The kinetic results from the gas-phase thermal isomerization of 5-amino-3,4-dimethylisoxazole (1), 3,5-dimethylisoxazole (2), and 3-amino-5-methylisoxazole (3) are reported.Compound 1 afforded quantitatively 3-carbamoyl-2,3-dimethyl-1-azirine (4).On the other hand, 2 and 3 gave the isomeric oxazoles 5 and 7, respectively.Different reaction pathways are discussed according to the activation parameters.
Capture of an elusive nitrile ylide as an intermediate in isoxazole-oxazole photoisomerization
Nunes, Claudio M.,Reva, Igor,Fausto, Rui
, p. 10657 - 10665 (2013/11/19)
The unimolecular photochemistry of 3,5-dimethylisoxazole (1) induced by a narrow-band tunable UV laser was studied using low-temperature matrix isolation coupled with infrared spectroscopy. Monomers of 1 were isolated in argon matrices at 15 K and characterized spectroscopically. Irradiation of matrix-isolated 1 at λ = 222 nm (near its absorption maximum) led to the corresponding 2H-azirine 3 and ketenimine 6 as primary photoproducts and also to nitrile ylide 4 and 2,5-dimethyloxazole (5). The photoproducts were identified (i) by comparison with infrared spectra of authentic matrix-isolated samples of 3 and 5 and (ii) using additional irradiations at longer wavelengths (where 1 does not react) which induce selective photoisomerizations of 4 and 6. In particular, irradiation with λ = 340 nm led to the unequivocal identification of the nitrile ylide anti-4, which was transformed into oxazole 5. The details of the 1,5-electrocyclization of the carbonyl nitrile ylide 4 and its structural nature (propargyl-like versus allene-like geometry) were also characterized using theoretical calculations. Thus, the elusive carbonyl nitrile ylide 4 was captured and characterized for the first time as an intermediate in the isoxazole-oxazole photoisomerization.
Gold catalysis: Mild conditions for the synthesis of oxazoles from N-propargylcarboxamides and mechanistic aspects
Hashmi, A. Stephen K.,Weyrauch, Jan P.,Frey, Wolfgang,Bats, Jan W.
, p. 4391 - 4394 (2007/10/03)
(Chemical Equation Presented) 2,5-Disubstituted oxazoles are synthesized from the corresponding propargylcarboxamides under mild reaction conditions via homogeneous catalysis by AuCl3. While monitoring the conversion via 1H NMR spectroscopy, an intermediate 5-methylene-4,5-dihydrooxazole can be observed and accumulated up to 95%, being the first direct and catalytic preparative access to such alkylidene oxazolines. The intermediate was fully characterized and can be trapped at -25°C for several weeks. Deuteration experiments show a stereospecific mode of the two first steps of the reaction.
