کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5230692 | 1383703 | 2007 | 6 صفحه PDF | دانلود رایگان |
Treatment of 3,4,5-tribromopyrazole with 1,2-dibromoethane and triethylamine gave 3,4,5-tribromo-1-vinylpyrazole, which underwent regioselective bromine-lithium exchange at the 5-position. Subsequent addition of an electrophile gave 5-substituted 3,4-dibromo-1-vinylpyrazoles. These underwent bromine-lithium or bromine-magnesium exchange predominantly at the 4-position, with the regioselectivity between the 3- and 4-positions being influenced by the nature of the metal and the 5-substituent. The 5-substituted products were de-vinylated by mild treatment with KMnO4 affording 3-substituted pyrazoles. Alternatively, the 1-vinyl group could be used in ring-closing metathesis. Thus, 5-allylthio-1-vinylpyrazole produced 5H-pyrazolo[5,1-b][1,3]thiazine upon treatment with Grubbs' second-generation catalyst.
Journal: Tetrahedron - Volume 63, Issue 1, 1 January 2007, Pages 56-61