Development of brominating agents for syntheses of alkyl bromides and acid bromides

Abstract

Two new brominating agents, ethyl tribromoacetate (Br₃CCO₂Et) and hexabromoacetone (Br₃CCOCBr₃) have been developed and utilized in combination with triphenylphosphine (PPh₃) for conversion of primary and secondary alcohols into the corresponding alkyl bromides in high yield under mild conditions within short reaction time. The general mechanism was believed to occur via S[sbiscript N]2 supporting by the evidence of the inversion of configuration of the analogous alkyl bromide. In addition, Br₃CCOCBr₃/PPh₃ could be utilized as an efficient reagent to prepare acid bromides form carboxylic acid. This developed methodology was efficiently applied for the synthesis of carboxylic acid derivatives such as amides, esters, acid anhydrides and thioesters in one-pot reaction. The stability of Br₃CCOCBr₃ at 80℃ and under UV irradiation was thoroughly studied and it was found that this reagent was quite stable and reactive with high chemoselectivity.