(E,E)-Cinnamylideneacetophenones 3a–j were epoxidized under mild conditions with Jacobsen's catalyst 4 and hydrogen peroxide or iodosylbenzene as oxidants. γ,δ-Monoepoxides and a diastereomeric mixture of α,β:γ,δ-diepoxides were obtained in each case, and only the α,β-monoepoxide of 4-nitrocinnamylideneacetophenone (3d) was isolated. The presence of a methyl group in the vinylic moiety of substrates 3i,j allowed the formation of two γ,δ-monoepoxide diastereomers. The epoxidation of (E,E)-2′-hydroxycinnamylideneacetophenones 3h,j led to the formation of the corresponding γ,δ-monoepoxides as well as (E)-2,3-trans-3-hydroxy-2-styryl-4-chromanones, which originated from the in situ cyclisation of 2,3-epoxy-1-(2-hydroxyphenyl)-5-phenyl-4-penten-1-ones. The structures of all new compounds and the stereochemistry of the mono- and diepoxide diastereomers were established by NMR studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)