Solvent free, light induced 1,2-bromine shift reaction of alpha-bromo ketones

초록

Photolysis of alpha-bromopropiophenones in acetonitrile results in formation of beta-bromopropiophenones with good product selectivity, which can be coined as 1,2-Br shift reaction. The product selectivity increases when the reaction is done in neat or solid state, where only the 1,2-Br shift product is formed in some cases. The reaction is suggested to proceed by C-Br bond homolysis to give a radical pair, followed by disproportionation and conjugate addition of HBr to the alpha,beta-unsaturated ketone intermediate. When the unsaturated intermediate is stabilized by an extra conjugation, the reaction stops at the stage, in which the unsaturated ketone becomes a major product. The synthetic method described in this research fits in a category of eco-friendly organic synthesis nicely since the reaction does not use volatile organic solvents and any other additives such as acid, base or metal catalysts, etc. Besides, the method fits into perfect atom economy, which does not give any side products. The synthetic method should find much advantage over other alternative methods to obtain beta-bromo carbonyl compounds. (C) 2018 Elsevier Ltd. All rights reserved.

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