- 65. Herstellung von substituierten 2-Aminooxazol-4-carbonitrilen.
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During our synthetic programme to convert 4-isoxazolylthioureas 3 into the corresponding carbodiimides 5, a side reaction leading to the hitherto unknown 2-aminooxazole-4-carbonitriles 6 was observed.By selecting appropriate reaction conditions, it was po
- Pascual, Alfons
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p. 556 - 569
(2007/10/02)
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- Flash Vacuum Pyrolysis of Some 4-Nitroisoxasoles
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Flash vacuum pyrolysis (FVP) of some 5-alkyl-3-methyl-4-nitroisoxasoles affords 1-nitro-1-cyanoacetone as the only product.A general mechanism is suggested which involves isomerization of the isoxazole to a 1-azirine.A nonclassical reaction of 3-methyl-4-nitroisoxazoles is assumed as a consequence of the electron-withdrawing ability of the nitro group, which precludes ring closure of the nitrile ylide intermediate to the oxazole isomer.The formation of 1-nitro-1-cyanoacetone by FVP of the 3-unsubstituted 5-methyl-4-nitroisoxazole suggests that the activation barrier for a 1,2-hydrogen shift from a 1-azirine or vinylnitrene is lower than that for the formation of nitrile ylide.The FVP of 5-ethyl-3-methylisoxzaole affords 5-ethyl-2-methyloxazole.
- Perez, Jorge Daniel,Wunderlin, Daniel A.
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p. 3637 - 3640
(2007/10/02)
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- Synthesis of 4(5)-Acyl-, 1-Substituted 5-Acyl, and 1-Substituted 4-Acyl-1H-imidazoles from 4-Aminoisoxazoles
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4-Aminoisoxazoles can be acylated with a wide variety of activated carboxylic acids.Hydrogenation of the resulting amides gives α-(acylamino)enaminones, which cyclize to 4(5)-acylimidazoles upon treatment with base.This method allows for the synthesis of acylimidazoles with a wide range of substituents at C-2.Utilization of N-substituted 4-aminoisoxazoles in the same sequence of reactions yields 1-substituted 5-acylimidazoles, a substitution pattern not otherwise easily prepared.Treatment of α-(acylamino)enaminones, derived from N-unsubstituted isoxazoles, with primary amines leads to incorporation of the amine at the β-position with concomitant expulsion of ammonia.This sequence efficiently yields 1-substituted and 1,2-disubstituted 4-acylimidazoles but does not give satisfactory yields of 5-substituted 4-acylimidazoles due to steric inhibition of the amine exchange.
- Reiter, Lawrence A.
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p. 2714 - 2726
(2007/10/02)
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