ISSN 1070-4280, Russian Journal of Organic Chemistry, 2012, Vol. 48, No. 4, pp. 519–522. © Pleiades Publishing, Ltd., 2012. Original Russian Text © Yu.V. Ostapyuk, V.S. Matiichuk, N.I. Pidlypnyi, N.D. Obushak, 2012, published in Zhurnal Organicheskoi Khimii, 2012, Vol. 48, No. 4, pp. 521–524. 519 Convenient Synthesis of α-Bromo Ketones by the Meerwein Reaction Yu. V. Ostapyuk, V. S. Matiichuk, N. I. Pidlypnyi, and N. D. Obushak Ivana Franko Lviv National University, ul. Kirilla i Mefodiya 6, Lviv, 79005 Ukraine e-mail: obushak@in.lviv.ua Received September 27, 2011 Abstract—A simple and convenient procedure was proposed for the synthesis of 4-aryl-3-bromobutan-2-ones from methyl vinyl ketone and arenediazonium bromides under Meerwein reaction conditions. α-Bromo ketones are widely used in organic syn- thesis [1], e.g., as difunctional electrophiles in the syn- thesis of heterocycles [1, 2] and intermediate products in the preparation of biologically active substances [3]. α-Bromo ketones are generally prepared by bromina- tion of the corresponding ketones with N-bromosuccin- imide or bromine in the presence of an acid [1, 4]. In recent time other synthetic approaches have also been proposed [5]. The present communication describes a new proce- dure for the synthesis of α-bromo ketones by reaction of methyl vinyl ketone with arenediazonium salts. Arylation of unsaturated compounds with diazonium salts (Meerwein reaction) provides a convenient method for the preparation of polyfunctionalized com- pounds [6, 7]. Bromoarylation of α, β-unsaturated ketones according to Meerwein was not described previously. We examined copper-catalyzed reaction of ben- zenediazonium bromide (Ia) with methyl vinyl ketone (IV). The reaction was carried out at room tempera- ture, by adding an aqueous solution of diazonium salt Ia to a solution of methyl vinyl ketone (IV) in acetone in the presence of a catalytic amount of copper(II) bromide. As a result, 3-bromo-4-phenylbutan-2-one (Va) was formed in a moderate yield (40%) together with bromobenzene (37%) as product of side Sand- meyer reaction. We also tried to synthesize compound Va by three-component reaction, i.e., using benzenedi- azonium tetrafluoroborate ( II ) or hydrogen sulfate (III) and potassium bromide instead of benzenediazo- nium bromide (Ia) (Scheme 1). In all cases, compound Va was isolated in approximately equal yields. Varia- tion of the solvent showed that no reaction occurs in nonpolar solvents, carboxylic acids, and alcohols. The reactions in DMF, DMSO, and dioxane gave, respec- tively, 14, 15, and 5% of compound Va. After having determined the optimal conditions, we extended the above reaction over a number of arene- diazonium salts Ia–Iq prepared by diazotization of the corresponding aromatic amines with sodium nitrite in 40% aqueous HBr. In all cases, bromo ketones Va–Vq were formed in 40–50% yield (Scheme 2). The reac- tion temperature was varied from 20 to 44°C, depend- ing on the substituent in the aromatic ring of initial diazonium salt I. The yield of bromo ketones Va–Vq increased when a mixture of methyl vinyl ketone (IV) and copper(II) bromide was preliminarily stirred over a period of 10 min (prior to addition of arenediazoni- um salt I ). Presumably, a complex of methyl vinyl DOI: 10.1134/S1070428012040094 Ia, X = Br; II, X = BF 4 ; III, X = HSO 4 . N 2 X – Ia, II, III + H 2 C Me O IV Va Br O Me CuBr 2 , Me 2 CO–H 2 O (X = Br) or KBr, CuBr 2 , Me 2 CO–H 2 O (X = BF 4 , HSO 4 ) Scheme 1.