Synthesis of 4(5)-acyl-, 1-substituted 5-acyl- and 1-substituted 4-acyl-1H-imidazoles from 4-aminoisoxazoles (original) (raw)
1987, The Journal of Organic Chemistry
4-Aminoisoxazoles can be acylated with a wide variety of activated carboxylic acids. Hydrogenation of the resulting amides gives a-(acylamino)enaminones, which cyclize to 46)-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 a-(acylamino)enaminones, derived from N-unsubstituted isoxazoles, with primary amines leads to incorporation of the amine at the P-position with concomitant expulsion of ammonia. This sequence efficiently yields 1-substituted and 1,2-disubstituted 4acylimidazoles but does not give satisfactory yields of 5-substituted 4-acylimidazoles due to steric inhibition of the amine exchange.
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