Bromination of 1,3,5-Trimethyl-4-Chloropyrazole

Article abstract of DOI:10.1007/BF00475561

The bromination of 1,3,5-trimethyl-4-chloropyrazole with N-bromosuccinimide (NBS) in the presence of benzoyl peroxide leads to 5-bromomethyl-1,3-dimethyl-4-chloropyrazole, whereas 3,5-bis(bromomethyl)-1-methyl-4-chloropyrazole predominates in the case of a twofold excess of NBS.Products of subsequent substitution in the 3- and 5-bromomethyl groups of the 3,5-bis(bromomethyl) compound in a ratio of 3:1 were detected in small amounts; this is evidently associated with the syn orientation of the bromine atom in the 5-bromomethyl group, which hinders attack by the bromine radical.