Tetrahedron

The N-vinyl group as a protection group of the preparation of 3 (5)-substituted pyrazoles via bromine–lithium exchange

B Iddon, JE Tønder, M Hosseini, M Begtrup

Index: Iddon, Brian; Tonder, Janne Ejrnaes; Hosseini, Masood; Begtrup, Mikael Tetrahedron, 2007 , vol. 63, # 1 p. 56 - 61

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Citation Number: 24

Abstract

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 ...