α-BROMINATION OF KETONES USING HEXABROMOACETONE

Abstract

The new synthetic method for α-bromoketones under mild conditions with short reaction time using hexabromoacetone (HBA) is disclosed. Propiophenone was used as a model substrate. Various factors including types of brominating agent, reaction time with UV-irradiation, solvents and molar ratio of propiophenone: HBA were scrutinized. The optimum conditions as the ratio of substrate to HBA (1:1) in THF at RT for 5 min under UV (254 nm) was uncovered. 2-Bromopropiophenone was obtained as a sole product in almost quantitative yield. The developed protocol could be successfully utilized for other selected ketones, such as acetophenone, 2-hydroxyacetophenone, 4-hydroxyacetophenone, 4-methoxyaceto-phenone, α-tetralone, cyclohexanone and 2-hexanone with moderate to high yield. Furthermore, α-bromination of certain ketones with HBA could be conducted in refluxing THF instead of using UV-irradiation. The scale-up of α-bromination of propiophenone into 2-bromopropiophenone was also attempted with success.