Microwave-induced synthesis and regio- and stereoselective epoxidation of 3-styrylchromones

The microwave-assisted solvent-free synthesis of (E)-3-styrylchromones from 3-formylchromones and phenylmalonic acid on sodium acetate support has been developed; the method affords the styryl derivatives in moderate to good yields and with complete diastereoselectivity. Protocols for the highly regioselective epoxidation of (E)- and (Z)-3-styrylchromones have been elaborated. Treatment of the alkenes with dimethyldioxirane led to the exclusive formation of 3-(3-aryloxiran-2-yl)chromones with complete diastereoselectivity, whereas treatment with hydrogen peroxide under alkaline conditions afforded the corresponding 2,3-epoxy-3-styrylchromanones as the only products. Epoxidation performed in the presence of chiral, nonracemic cinchona-alkaloid-based quaternary ammonium salts allowed the synthesis of enantiomerically enriched 2,3-epoxy-3-styrylchromanones, but with only moderate ee values. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).