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.
Manifestation of zeolitic pore characteristics of modified montmorillonite in oxazole synthesis by propargylation and cycloisomerization reactions
Venkatesha,Bhat,Jai Prakash
, p. 51 - 57 (2015)
Zeolitic micropores are found to be developed on montmorillonite clay by treatment with phenoldisulphonic acid (PDSA). The micropores developed have the ability to enhance the cycloisomerization of the alkynylamide to form oxazole product. Pore characteristics by surface measurement techniques and acidity by pyridine adsorption using FT-IR were evaluated. Surface measurements showed significant increase in the surface area, acidity and the micropore volume but neither of them correlated well with the cycloisomerization activity. Variation in Br?nsted and Lewis acidity and pore volume by surface coverage using Br?nsted (B) and Lewis (L) acid compounds, caused variation in cycloisomerization activity. Best correlation with the amount of oxazole formed was observed when volume accessibility factor (VAF), a product of micropore volume and ratio of B to L acidity were considered. Based on this, a reaction scheme for cycloisomerization is proposed involving both B and L sites within the micropores.
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.
The pyrolysis of isoxazole revisited: A new primary product and the pivotal role of the vinylnitrene. A low-temperature matrix isolation and computational study
Nunes, Claudio M.,Reva, Igor,Pinho E Melo, Teresa M. V. D.,Fausto, Rui,Solomek, Tomas,Bally, Thomas
supporting information; experimental part, p. 18911 - 18923 (2012/02/05)
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.
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.
Antibacterial monic acid derivatives
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, (2008/06/13)
A compound of the formula (I) STR1 wherein R is a group STR2 R1 is hydrogen, phenyl, C1-20 alkyl, C2-8 alkenyl or C2-8 alkynyl each of which may optionally be substituted; or C3-7 cycloalkyl, X is a divalent group --Y--C=C--, and Y is oxygen or sulphur, have antibacterial and/or antimycoplasmal activity.
Base-Catalyzed Cyclization of N-Propargylamides to Oxazoles
Nilsson, Bjoern M.,Hacksell, Uli
, p. 269 - 275 (2007/10/02)
The base-catalyzed cyclization of some N-propargylamides to oxazoles has been studied in the presence of sodium hydride and potassium carbonate.The α-arylsubstituted propargylamides 1c-d (Ar = p-OMeC6H4 (1c), C6H5 (1d), and p-O2NC6H4 (1e)) cyclized with markedly higher rates (1e > 1d > 1c) than the unsubstituted and α-methyl substituted propargylamides 1a and 1b.A 1H nmr spectroscopic experiment demonstrated the presence of an allenic intermediate in the potassium carbonate-catalyzed ring closure of 1e.The observed rank order of reactivities correlates well withthe acidities of the respective propargylic hydrogens of the amides and with the ability of the ring closed intermediates to stabilize an oxazole anion.The results demonstrate that the base-catalyzed formation of oxazoles from propargylamides may proceed via an allenic intermediate.
