Selenium Dioxide-Mediated Bromination of α,β-Unsaturated Ketones Using N‑Bromosuccinimide in the Presence of p‑Toluenesulfonic Acid: A Versatile Route for the Synthesis of α′-Bromo-4-arylbut-3-en-2-one and α′,α′-Dibromo-4-arylbut-3-en-2-one

An efficient method for the synthesis of α,β-unsaturated α′-bromoketones and α,β-unsaturated α′,α′-dibromoketones is described using N-bromosuccinimide (NBS) as the brominating agent mediated by selenium dioxide (SeO2) in the presence of p-toluenesulfonic acid (PTSA) monohydrate in toluene. The method is simple, employing easily available shelf reagents to afford a wide range of products in good yields. The method highlighted that simple fine-tuning of the reaction conditions and molar equivalents of the reactants easily affords either mono- or dibrominated products in excellent yields. A number of these products have not been reported in the literature. All of the reactions were carried out in gram-scale quantities.