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 ...
