Categories: Synthesis of N-Heterocycles, Synthesis of O-Heterocycles >
Synthesis of isoxazoles
Recent Literature
A large number of functionally substituted 2-alkyn-1-one O-methyl oximes
have been cyclized under mild reaction conditions in the presence of ICl to give
the corresponding 4-iodoisoxazoles in moderate to excellent yields. The
resulting 4-iodoisoxazoles undergo various palladium-catalyzed reactions to
yield 3,4,5-trisubstituted isoxazoles.
J. P. Waldo, R. C. Larock, J. Org. Chem., 2007,
72, 9643-9647.
The direct regioselective synthesis of 3,5-disubstituted isoxazoles was achieved
through a sequence involving a net bromination of an electron-deficient alkene,
in situ generation of a nitrile oxide, 1,3-dipolar cycloaddition, and loss of
HBr from an intermediate bromoisoxazoline. This one-pot process enables the
direct synthesis of 3,5-disubstituted isoxazoles from electron-deficient
alkenes.
J. Xu, A. T. Hamme II, Synlett, 2008,
919-923.
The consecutive Sonogashira coupling of acid chlorides with terminal alkynes,
followed by 1,3-dipolar cycloaddition under dielectric heating of in situ
generated nitrile oxides from hydroximinoyl chlorides furnishes isoxazoles in
moderate to good yields in the sense of a one-pot three-component reaction.
B. Willy, F. Rominger, T. J. J. Müller, Synthesis, 2008,
293-303.
A 1,3-dipolar cycloaddition of phenyl vinylic selenide to nitrile oxides and
subsequent oxidation-elimination furnished 3-substituted isoxazoles with
good yields in a one-pot, two-step transformation.
S.-R. Sheng, X.-L. Liu, Q. Xu, C.-S. Song, Synthesis, 2003, 2763-2764.
The dehydration of primary nitro compounds can be performed by bases in the
presence of dipolarophiles. Among the organic bases examined, DABCO gave the
best results. The reaction is applicable to activated nitro compounds and to
phenylnitromethane and affords isoxazoline derivatives in higher yields
compared with those of other methods. The reaction, however, is not
compatible with nitroalkanes.
L. Cecchi, F. De Sarlo, F. Machetti, Eur. J. Org. Chem., 2006,
4852-4860.
3,5-Disubstituted isoxazoles are regioselectively obtained in good yields by
a mild and convenient one-pot, three-step procedure utilizing a
copper(I)-catalyzed cycloaddition reaction between in situ generated
nitrile oxides and terminal acetylenes.
T. V. Hansen, P. Wu, V. V. Fokin, J. Org. Chem., 2005, 70, 7761-7764.
Pyrazole or isoxazole derivatives are prepared by a palladium-catalyzed four-component coupling of a terminal alkyne, hydrazine (hydroxylamine),
carbon monoxide under ambient pressure, and an aryl iodide.
M. S. M. Ahmed, K. Kobayashi, A. Mori, Org. Lett.,
2005, 7, 4487-4489.
The reaction of
various 2-alkyn-1-one O-methyl oximes with ICl, I2, Br2, or PhSeBr
provided 3,5-disubstituted 4-halo(seleno)isoxazoles
in good to excellent yields under mild reaction conditions.
J. P. Waldo, R. C. Larock, Org. Lett.,
2005, 7, 5203-5205.
A series of 4-alkyl-5-aminoisoxazoles have been synthesized in high yield by
nucleophilic addition of lithiated alkyl nitriles to (α)-chlorooximes.
M. P. Bourbeau, J. T. Rider, Org. Lett.,
2006, 8, 3679-3680.
3-Acylisoxazoles were synthesized by the reaction of alkenes or alkynes with
ketones (acetone or acetophenone), as both a reagent and the solvent, by
three methods: iron(III) nitrate under reflux, iron(III) salt-nitrogen
dioxide (NO2) at room temperature, and iron(III) nitrate under microwave
irradiation (MW).
K.-I. Itoh, H. Sakamaki, N. Nakazato, A. Horiuchi, E. Horn, C. A. Horiuchi, Synthesis, 2005, 3541-3548.
