The conversion of isothiazoles into pyrazoles using hydrazine
摘要:
The conversion of isothiazoles into pyrazoles on treatment with hydrazine is investigated. The influence of various C-3, C-4 and C-5 isothiazole substituents and some limitations of this ring transformation are examined. When the isothiazole C-3 substituent is a good nucleofuge, 3-aminopyrazoles are obtained. However, when the 3-substituent is not a leaving group it is retained in the pyrazole product. Treatment of 4-bromo-3-chloro-5-phenylisothiazoie 56 or 3-chloro-4,5-diphenylisothiazole 57 with anhydrous hydrazine at ca. 200 degrees C for a few minutes gives the corresponding 3-hydrazinoisothiazoles 61 and 64 respectively in high yields; the stability of these new hydrazines is investigated. 5,5'-Diphenyl-3,3'-biisothiazole-4,4'-dicarbonitrile 78 reacts with hydrazine to give 5,5'-diphenyl-3,3'-bi(1H-pyi-azole)-4,4'-dicarbonitrile 79. Methylhydrazine reacts with 3-chloro-5-phenytisothiazole-4-carbonitrile 1 to give 3-(1-methylhydrazino)-5-phenylisothiazole-4-carbontrile 83 and 3-amino-lmethyl-5-phenylpyrazole-4-carbonitrile 84. All products are fully characterised and rational mechanisms for the isothiazole into pyrazole transformation are proposed. (C) 2009 Elsevier Ltd. All rights reserved.
The conversion of isothiazoles into pyrazoles using hydrazine
摘要:
The conversion of isothiazoles into pyrazoles on treatment with hydrazine is investigated. The influence of various C-3, C-4 and C-5 isothiazole substituents and some limitations of this ring transformation are examined. When the isothiazole C-3 substituent is a good nucleofuge, 3-aminopyrazoles are obtained. However, when the 3-substituent is not a leaving group it is retained in the pyrazole product. Treatment of 4-bromo-3-chloro-5-phenylisothiazoie 56 or 3-chloro-4,5-diphenylisothiazole 57 with anhydrous hydrazine at ca. 200 degrees C for a few minutes gives the corresponding 3-hydrazinoisothiazoles 61 and 64 respectively in high yields; the stability of these new hydrazines is investigated. 5,5'-Diphenyl-3,3'-biisothiazole-4,4'-dicarbonitrile 78 reacts with hydrazine to give 5,5'-diphenyl-3,3'-bi(1H-pyi-azole)-4,4'-dicarbonitrile 79. Methylhydrazine reacts with 3-chloro-5-phenytisothiazole-4-carbonitrile 1 to give 3-(1-methylhydrazino)-5-phenylisothiazole-4-carbontrile 83 and 3-amino-lmethyl-5-phenylpyrazole-4-carbonitrile 84. All products are fully characterised and rational mechanisms for the isothiazole into pyrazole transformation are proposed. (C) 2009 Elsevier Ltd. All rights reserved.
The conversion of isothiazoles into pyrazoles using hydrazine
作者:Heraklidia A. Ioannidou、Panayiotis A. Koutentis
DOI:10.1016/j.tet.2009.06.041
日期:2009.8
The conversion of isothiazoles into pyrazoles on treatment with hydrazine is investigated. The influence of various C-3, C-4 and C-5 isothiazole substituents and some limitations of this ring transformation are examined. When the isothiazole C-3 substituent is a good nucleofuge, 3-aminopyrazoles are obtained. However, when the 3-substituent is not a leaving group it is retained in the pyrazole product. Treatment of 4-bromo-3-chloro-5-phenylisothiazoie 56 or 3-chloro-4,5-diphenylisothiazole 57 with anhydrous hydrazine at ca. 200 degrees C for a few minutes gives the corresponding 3-hydrazinoisothiazoles 61 and 64 respectively in high yields; the stability of these new hydrazines is investigated. 5,5'-Diphenyl-3,3'-biisothiazole-4,4'-dicarbonitrile 78 reacts with hydrazine to give 5,5'-diphenyl-3,3'-bi(1H-pyi-azole)-4,4'-dicarbonitrile 79. Methylhydrazine reacts with 3-chloro-5-phenytisothiazole-4-carbonitrile 1 to give 3-(1-methylhydrazino)-5-phenylisothiazole-4-carbontrile 83 and 3-amino-lmethyl-5-phenylpyrazole-4-carbonitrile 84. All products are fully characterised and rational mechanisms for the isothiazole into pyrazole transformation are proposed. (C) 2009 Elsevier Ltd. All rights reserved.