- Synthesis of silylated β-enaminones and applications to the synthesis of silyl heterocycles
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Silyl β-enaminones have been synthesized by reductive cleavage of silylisoxazoles. These versatile synthons bearing the silyl group in different positions of the enamino ketonic system are of great interest in the construction of a variety of penta- and hexaheterocycles, which, in general, retain the silyl group attached at the ring or in a side chain.
- Calvo, Luis A.,González-Nogal, Ana M.,González-Ortega, Alfonso,Sa?udo
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p. 8981 - 8984
(2007/10/03)
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- Reactions of β-aminoenones with acetylhydrazine, semicarbazide and methoxycarbonylhydrazine. Synthesis of 1-acetyl-, 1-carboxamide- or methyl 1- carboxylated pyrazole derivatives
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Acetylhydrazine, semicarbazide and methoxycarbonylhydrazine react with β-aminoenones to give regioselectively the corresponding N-acetyl- or N- carboxypyrazole derivatives. The reaction are highly regioselective and occurs via 5-hydroxypyrazolines which in several case can be isolated and characterized.
- Alberola, Angel,Calvo, Luis,Ortega, Alfonso Gonzalez,Sadaba, M. Luisa,Sanudo, M. Carmen,Granda, Santiago Garcia,Rodriguez, Elena Garcia
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p. 2675 - 2686
(2007/10/03)
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- ORGANIC REACTIONS IN THE AQUEOUS MEDIUM Part VI. Synthesis of Substituted Pyrazoles and Pyrazolones
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The reactions of semicarbazide hydrochloride and hydrazine monohydrate with ethyl acetoacetate, acetylacetone, benzoylacetone and dibenzoylmethane leading to the formation of pyrazole and pyrazolone derivatives have been intensively studied in the aqueous as well as in the nonaqueous medium under various sets of conditions. This has resulted in the development of simple and convenient methods for the synthesis of pure ethyl acetoacetate semicarbazone (I), 3-methylpyrazol-5-one-1-carboxamide (II), 3-methylpyrazol-5-one (III), 3,5-dimethylpyrazol-1-carboxamide (V), 3,5-dimethylpyrazole (VI), 3-phenyl-5-methylpyrazole-1-carboxamide (VII), 3-phenyl-5-methylpyrazole (VIII) and 3,5-diphenylpyrazole (IX). It has been suggested that the reaction of semicarbazide hydrochloride with β-diketo compounds proceeds through four stages. A reaction scheme has been proposed to explain the formation of different products. Key words.Synthesis, Pyrazole and Pyrazolone derivatives.
- Ali, Sh. Shaukat,Ashraf, C. M.,Younas, M.,Ehsan, A.
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p. 502 - 510
(2007/10/02)
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- An Improved Synthesis of 3,6-Diamino-1,2,4,5-tetrazine. I
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Treatment of 1,3-diaminoguanidine monohydrochloride (1) with 2,4-pentanedione (2) in alcohols under carefully controlled conditions gave 3,6-diamino-1,2-dihydro-1,2,4,5-tetrazine monohydrochloride (3) in 45-50percent yields along with 3,5-dimethyl-1H-pyrazole (4) and its hydrochloride 5.Oxidation of 3 with sodium perborate produced 3,6-diamino-1,2,4,5-tetrazine (6) in quantitative yield.
- Coburn, Michael D.,Ott, Donald G.
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p. 1941 - 1945
(2007/10/02)
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- Synthesis of 1-Oxo-1H-pyrazolotriazol-4-ium-3-olates. - A Ring-Chain Tautomerism in the Series of Bicyclic Dipolar Heterocycles
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1-(Trimethylsilyl)pyrazole (12) reacts with chlorocarbonyl isocyanate to give a compound, which - dependent on the state of aggregation - may exist both as a bicyclic dipolar heterocycle (7) and as monocyclic 1-pyrazolyl carbonyl isocyanate (8).Methyl-substituted derivatives (19a, b) show a similar behaviour.MNDO calculations for the parent systems (7, 8) are in accord with these experimental observations.The structure of 5,6,7-trimethyl-1-oxo-1H-pyrazolotriazol-4-ium-3-olate (19b) has been clarified by X-ray analysis.
- Boettcher, Andreas,Debaerdemaeker, Tony,Radziszewski, Juliusz G.,Friedrichsen, Willy
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p. 895 - 908
(2007/10/02)
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