Synthesis of alpha,beta-dibromo ketones by photolysis of alpha-bromo ketones with N-bromosuccinimide: Photoinduced beta-bromination of alpha-bromo ketones

Abstract

Irradiation of alpha-bromopropiophenones in the presence of NBS results in the formation of alpha,beta-dibromopropiophenones, which can be viewed as beta-bromination of alpha-bromopropiophenones. The reaction is believed to go through a series of reactions; photoinduced C-Br bond cleavage, elimination of HBr to give alpha,beta-unsaturated ketone intermediates, and addition of Br-2, which are formed by the reaction between HBr and NBS. From mechanistic studies of the reaction, we have also found a very convenient method for alpha-debromination of the alpha,beta-dibromopropiophenones which is by simple irradiation of the dibromo ketones in acetone or 2-propanol without the use of any additives. Our results demonstrate that bromine can be added into or eliminated from the alpha, beta, or both positions to the carbonyl group by photochemical methods, which make synthetic options of bromine containing carbonyl compounds versatile. (C) 2019 Elsevier Ltd. All rights reserved.