Enamines with molecular bromine

Interpretation of these studies, as well as those involving reaction with methyl acrylate and acrylonitrile as electrophiles, are complicated by the possibility that these reactions are reversible. Conversely, reaction with molecular bromine is considerably faster than regioisomerization, an observation that has been used to prepare separate samples of 2-bromo-6-methyl- and 2-bromo-2-methyl-cyclohexanone. Thus, in the reaction of a nearly one to one mixture of the less and more substituted enamines derived from methylcyclohexanone with 0.5 equiv. of bromine, only the less substituted isomer is converted to the intermediate immonium ion, which precipitates from ether solution at -50 C (Scheme 8). Separation, and then addition of more bromine to the filtrate, then effected reaction of the more substituted isomer. 

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