The electrophilic addition of dimethylbromosulfonium bromide to conjugated enones: efficient synthesis of α-bromo enones

Dimethylbromosulfonium bromide reacted readily with many enones at 0 °C or lower to precipitate a-bromo-β-sulfonium conjugated enones. These salts eliminate a proton and dimethylsulfide readily with aqueous potassium carbonate to give excellent yields of α-bromo conjugated enones cleanly. The mechanism of the addition was explained by the bromonium ion initiated 1,4-addition followed by tautomerization of enol hypobromites.