Microwave Promoted Epoxidation of a,b-Unsaturated Ketones in Aqueous Sodium Perborate$ Ali Sharifi,* Mohammad Bolourtchian and Farshid Mohsenzadeh Chemistry & Chemical Engineering Research Center of Iran, P.O. Box 14335-186, Tehran, Iran A series of ,-unsaturated ketones has been treated with sodium perborate in water and 1,4-dioxane under microwave irradiation to produce ,-epoxyketones in good yields. Recently, there has been growing interest in applying micro- wave dielectric heating to accelerate organic reactions.1 Oxidation reactions are less considered under microwave irradiation due to unsafe and uncontrollable experimental conditions.2 Sodium perborate is a very cheap and widely used industrial chemical which is utilized as an oxidizing agent in organic chemistry:3 oxidation of anilines, sulRdes, ketones, hydroquinones, aromatic aldehydes, iodoarenes, aromatic nitriles, azines, sulfur heterocycles, benzylic alco- hols, a-hydroxycarboxylic acids, 1,2-diketones, a-hydroxy- ketones, 1,2-diols, unsaturated compounds and oximes under di€erent conditions have been reported.4 a,b-Unsaturated ketones react with sodium perborate in water and a cosolvent to produce the corresponding epoxides over a long period of time.5 Tetrahexylammonium hydrogensulfate is used as a phase transfer catalyst for these reactions, in both biphasic solvent mixtures6 and monophasic aqueous solutions7 at di€erent temperatures to enhance the rate and the yield of products.In this paper, we report epoxidation of a,b-unsaturated ketones by sodium perborate in water and a cosolvent (1,4-dioxane) under microwave irradiation for 2�}3 min to produce the corre- sponding epoxides in good yields (Scheme 1, Table 1). As seen in Table 1, the isolated yield under micro- wave conditions is higher than in thermal reactions. Regio- J. Chem. Research (S), 1998, 668�}669$ Scheme 1 Table 1 Epoxidation of a,b-unsaturated ketones with sodium perborate under microwave irradiation Entry Substrate Product Sodium perborate/substrate (mole ratio) Irradiation time/min Microwave yielda (%) Thermal yieldb (%) 1 3 2 92c (85)d 88c(55)d 2 3 2 100(73) 67(38) 3 2 51(43) 3 3 3 79(68) 78(60) 4 2 84(75) 4 3 3 88(82) 91(56) 5 3 2 83(79) 100(26) 3 3 86(80) 6 3 2 100(93) �} aAll products were characterized by IR, 1H NMR and their spectroscopic data were similar to those reported.bFrom ref. 5. The time of thermal reactions were 5�}26 h.cGC yield. dIsolated yield. speciRcity is observed for entry 4; the spectral data are identical to those of the known compound.5 Other co- solvents such as THF, DMSO, DMF were examined along $This is a Short Paper as deRned in the Instructions for Authors, Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is there- fore no corresponding material in J. Chem. Research (M). *To receive any correspondence (e-mail: ccerci@neda.net) 668 J. CHEM. RESEARCH (S), 1998with water.We observed a lower yield with those solvents than with 1,4-dioxane, under the same conditions. The opti- mum amount of sodium perborate is found to be 3 molar equivalents with respect to the substrate. Irradiation was carried out 3 or 4 times (each time for 15±20 s with 5 min intervals), in order to avoid increase of pressure in the closed Te�on vessel. In conclusion, we have reduced the reaction time com- pared with the thermal method.5 The isolated yields are higher than previously reported.5±7 The reaction constitutes a safe, mild, easy to work-up and convenient method for the synthesis of a,b-epoxyketones.Experimental IR spectra were obtained on a Perkin-Elmer 833 spectrometer, 1H NMR spectra on a Bruker 80 MHz in CDCl3 using Me4Si as internal standard. Microwave induced reactions were carried out in a Moulinex MICRO-CHEF, 900 W at 2450 MHz. General Procedure for Epoxidation of ,-Unsaturated Ketones.� A mixture of ketone (3 mmol) and sodium perborate (9 mmol) in water (9 mL) and 1,4-dioxane (6 mL) in a closed Te�on vessel (volume 250 mL) was irradiated for 2 min (four times, each time 30 s with 5 min intervals). After cooling, the mixture was extracted with dichloromethane (320 mL).The organic layer was separated and dried over magnesium sulfate. After ®ltration the solvent was evaporated and the residue analysed by GC and puri®ed with a short column (eluent: light petroleum±dichloromethane, 10:1).Received, 21st May 1998; Accepted, 14th July 1998 Paper E/8/03846E References 1 S. Galema, Chem. Soc. Rev., 1997, 26, 233; F. Langa, P. De la Cruz, A. De la Hoz, A. Diaz-Ortiz and E. Diez-Barra, Con- temporary Org. Synth., 1997, 373; R. A. Abramovitch, Org. Prep. Proc. Int., 1991, 23, 683; D. M. P. Mingos and D. R. Baghurst, Chem. Soc. 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