Halogenation of N-Oxygenated Pyrazoles. Preparation of N-Oxygenated 4-Halopyrazole and 4,4-Dihalo-4H-pyrazole Derivatives

Article abstract of DOI:10.1021/jo01289a017

Reaction of some 1-hydroxypyrazoles and 1-hydroxypyrazole 2-oxides with iodine or with 1 equiv of N-chloro- or N-bromosuccinamide (NCS or NBS) gives high yields of the 4-halo derivatives.With 2 equiv of NBS or NCS or with tert-butyl hypochlorite the products are 4,4-dihalo-4H-pyrazole 1-oxides or 1,2-dioxides.Reaction of 3,5-diphenylpyrazole with 2 equiv of tert-butyl hypochlorite gives 1,4-dichloro-3,5-diphenylpyrazole, which rearranges to 4,4-dichloro-3,5-diphenyl-4H-pyrazole.Silver ion assisted solvolysis of the gem-dihalides to form 4-chloro-3H-pyrazole derivatives is described.