Epoxidation of (E,E)‐Cinnamylideneacetophenones with Hydrogen Peroxide and Iodosylbenzene with Salen‐Mn^III as the Catalyst

Abstract

Keywords: Cinnamylideneacetophenones / Epoxidation / Jacobsen's catalyst / Hydrogen peroxide / Iodosylbenzene (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)-2Ј-hydroxycinnamylid-

Dimethyldioxirane Oxidation of Exocyclic (E,E)-Cinnamylideneketones

“…From the 2D-COSY experiments, all the proton resonances of the α,β:γ,δ-diepoxide system were assigned, H-3 (doublet at δ H 3.24-3.70), H-2 (double doublet at δ H 2.97-3.18), and H-3 (doublet at δ H 3.90-4.69). The coupling constant values J H2 -H3 ∼1.7-2.1 Hz are consistent with a trans configuration of the γ,δ-epoxide, [9,14] whereas those of J H3 -H2 are dependent on the size of the cyclanone ring and on the stereochemistry of the diastereomers (4a-c, J 3.8-4.9 Hz for A and J 5.6-6.0 Hz for B; 4d-f, J 4.4-6.0 Hz for A and J 6.1-6.6 Hz for B; 4g-i, J 5.0-6.3 Hz for A and J 6.8-7.2 Hz for B). The aromatic region of the 1 H NMR spectra of α,β:γ,δ-diepoxides 4a-i presents several multiplets, which were assigned with the aid of all 2D NMR spectra.…”

“…This effect results in the formation of the α,β-monoepoxides 5a-c from the oxidation of orthonitro-2-cinnamylidenebenzacyclanones 3c,f,i, as in the case of the epoxidation of 4-nitrocinnamylideneacetophenone with iodosylbenzene and a catalytic amount of salen Mn III . [9] NMR Spectroscopy The main features of the 1 H NMR spectra of 2-cinnamylidenebenzocyclanones 3a-i are the resonances of their vinylic protons. H-3 appears as a doublet, as a result of the coupling with H-2 at δ H 7.0-7.2 ppm and the coupling constant 3 J H3 -H2 15-16 Hz indicates the trans configuration of the C2 =C3 double bond.…”

“…[7] Previously, we also investigated the epoxidation of (E,E)-cinnamylideneacetophenones with different oxidizing agents. [8,9] When isolated dimethyldioxirane was used as oxidant, diastereomeric mixtures of α,β:γ,δ-diepoxides were obtained, in some cases together with α,β-monoepoxides as minor by-products. When (E,E)-2 -hydroxycinnamylideneacetophenones were oxidized under the same reaction conditions, 2 -hydroxy-γ,δ-epoxycinnamylideneacetophenones could also be detected and isolated.…”

Tandem mass spectrometry based investigation of cinnamylideneacetophenone derivatives: valuable tool for the differentiation of positional isomers

“…The (β,γ)(1,2) A + , α,β B + and (0,α)(1,2) B + product ions are observed in all the nitro derivatives 2 and 2a–k ; MS 2 spectra and their structures are shown in Scheme . The concurrent cleavage of the C1–C2 bond and C0–Cα, and a one proton transfer, lead to the formation of a primary carbocation, but a ‐hydrogen shift allows the formation of a more stable tertiary carbocation (0,α)(1,2) B + ( 16 , Scheme ) at m/z at 145 ( m/z 175 and 190 for 2c and 2d , respectively) observed in all the MS 2 spectra. The cleavage of the C1–C2 bond also occurs simultaneously with the cleavage of Cβ–Cγ leading to the formation of the product ion (β,γ)(1,2) A + ( 17 , Scheme ), common to all the nitro compounds.…”

“…( E , E )‐1,5‐Diarylpenta‐2,4‐dien‐1‐ones (cinnamylideneacetophenones) are a well‐known and important group of unsaturated ketones that have been widely used in a variety of synthetic transformations . One important use of these derivatives is their exploitation as very simple starting materials to construct cyclohexane derivatives with five new stereocenters.…”