Applications of hexabromoacetone for protection-deprotection of acetals and ketals and for bromination of alkanes and dicarbonyl compounds

Abstract

Hexabromoacetone (HBA) has been discovered for over a hundred years, but only a few of its applications have been reported. The carbon-bromine bond is generally weak and could be cleaved by UV irradiation, generating radicals that could be used for activating various reactions. In this research, HBA was used as a catalyst for protection of glycerol with acetone to form solketal, protection of benzaldehyde with methanol, protection of a variety of aldehydes and ketones with 1,3-propanedithiol, deprotection of benzaldehyde dimethyl acetal and other acetals, and deoximation of various oximes. The protection and deprotection were very fast and in most cases provided very high yields of the desired products using very small amount of HBA. Tested by a radical trapping reagent, the reactions likely proceeded via radical intermediates. Additionally, HBA was utilized as a brominating agent for the bromination of adamantane and diethyl malonate at room temperature under UV irradiation. The bromination of adamantane provided good yield and excellent selectivity of 1-bromoadamantane, while diethyl malonate can be both mono- and dibrominated depending on the reaction time and amount of HBA. Approximately 4 out of 6 bromine atoms of HBA can be used for bromination.