Stilbenes, epoxidation

All the reactions were carried out at 0°C, with the substrate (1 equivalent), ketone (3 equivalents), Oxone (5 equivalents), and NaHCC>3 in CH3CN aqueous EDTA for 2 hours. High enantioselectivity can generally be obtained for trans- and trisubstituted olefins. The favored spiro and planar transition states have been proposed for ketone 130-mediated rrans-stilbene epoxidation (Scheme 4-48). 

Like the trichloromethyl peroxide radical, peroxothio compounds can perform even nucleophilic oxygenation of substrates that are inert to Oj" in aprotic solvents. For example, stilbene is not changed in dry benzene containing 18-crown 6-ether and KOj. In the presence of diphenylsul-fide, however, the interaction takes place and results in the formation of stilbene epoxide. According to Oae et al. (1981), stilbene initially gives PhCH(00 )CH Ph anion-radical adduct. Abstraction of O from the adduct leads to stilbene epoxide with 40% yield (Oae et al. 1981). 

Table 9. Aminolytic kinetic resolution (AKR) of tra/is-stilbene epoxides using recyclable catalysts with aniline under different reaction conditions...

Figure 10.2 UV/Vis spectra for (a) RuCb in ethanol, (b) Ru2(p-cymene)2Cl4 in CH2CI2, (c) 1 in CH2CI2, (d) the supported Ru complex 3, (e) the unsaturated Ru complex (5) activated by 02/iBA and (f) the supported Ru catalyst after 100 cycles of stilbene epoxidation. Spectra (a)-(c) were measured in a transmission mode (left-hand axis abs) and (d)-(f) in a diffuse reflectance mode (left-hand axis KM).

Table 10.1 Catalytic activities of Ru catalysts for stilbene epoxidation .

The three-coordinated unsaturated structure of the Ru complex remained unchanged after 1000 cycles of the stilbene epoxidation as suggested by XPS, DR-UV/Vis and XAFS. The unsaturated Ru complex 5 is active for the epoxidation reaction. Notably, the three-coordinate Ru complex 5 is quite stable under the reaction conditions and also in air despite its unsaturated structure. This remarkable stability and durability made the immobilized catalyst 5 recyclable for the catalytic reactions, maintaining 100% conversion with selectivity higher than 80% [17]. 

E-Stilbene (18 mg, 0.1 mmol) and ketone (3.8 mg, 0.01 mmol) were dissolved in CH3CN (1.5 mL) at r.t. An aqueous Na2(EDTA) solution (1 mL, 4 x 10-4 M) was added. To the stirred mixture was added in portions a mixture of Oxone (307 mg, 0.5 mmol) and sodium bicarbonate (130 mg, 1.55 mmol). On completion of the reaction according to TLC analysis (20 min), the reaction mixture was poured into water (20 mL) and extracted with CH2CI2 (3 x 20 mL). The combined organic layers were dried over anhydrous Na2S04. After removal of the solvent under reduced pressure, the residue was purified by flash column chromatography on silica gel (hexane, then 95 5 hexanes ethyl acetate) to give trans-stilbene epoxide (19.4 mg, 99% yield) in 47% ee. 

In fact, the addition of BQ (10 3 M) to the reaction mixture reduced the rate of formation of benzaldehyde and minor products such as trans-stilbene epoxide and benzil, whereas no effect on the yield of eiy-stilbene was observed (Scheme 4). 

Si04)Mn2ln- Wu036H6]4-,[Mn4n- (H20)2(PW9034)2]10- stilbene cisjtr aws-stilbene epoxides... 

The reagent catalyzes the isomerization of epoxides to carbonyl compounds. Thus frans-stilbene epoxide reacts to give desoxybenzoin and diphenylacetaldehyde... 

P. Lignier, F. Morfin, S. Mangematin, L. Massin, J.-L. Rousset, V. Caps, Stereoselective stilbene epoxidation over supported gold-based catalysts, Chem. Commun. (2007) 186. 

Finally, we address the question of the reasons for the superiority of Co(II) compounds as the catalysts for the alkene epoxidation by 02/aldehyde system. We have studied the catalytic activity of Co(II) compounds using imKS-stilbene as a model substrate. Kinetic curves for the Iran -stilbene epoxide accumulation are given in Fig. 3. The kinetic curves show autocatalytic character. The time of the complete alkene conversion depends on both the induction time and the rate of the reaction after the completion of the induction period. It should be noted that the induction time increases considerably with decreasing aldehyde concentration and goes through a maximum with increasing Co(II) concentration (in the range 10 - 10 M). One can see from Fig. 3 that the rate of the epoxidation lowers in the order PW1 iCo, CoW 12 > CoNaY, Co(N03)2 >CoPc. 

We have studied efficiency of MNaY and MNaZSM-5 type zeolites with M= Co(II), Cu(II), Ni(n) and Fe(III) in aerobic epoxidation using /roras-stilbene as model substrate and isobutyraldehyde (IBA) as reductant. The results are summarized in Table 1. Trons-stilbene epoxide was found to be the main oxidation product, isobutyric add being the main product of transformation of IBA. Order of the catalytic activity of the metal ions introduced into NaY zeolites (Co > Cu Ni, Fe, NaY) is similar to that obtained previously for M-substituted heteropolytungstates [13]. Pronounced catalytic activity of CoNaY and NiNaY zeolites was earlier observed for co-oxidation of linear alkenes with acetaldehyde at 70°C [15]. The extents of ion exchange that can be attained for NaZSM-5 catalysts are less than those for NaY... 

The epoxide hydrolases are very important enzymes that render the epoxides formed by CYP enzymes harmless. Mammals have three distinct epoxide hydrolases. One microsomal form is specific for cholesterol-5,6a-oxide. It is induced by the same substances that induce the CYP enzymes. Another, less specific epoxide hydrolase is located in the endoplasmatic reticulum close to the CYP enzymes and is more important for xenobiotic substances. A third type, of some importance, is located in the cytosol. A typical substrate is trans-stilbene oxide, which also is an inducer. Some epoxides, such as diel-drin, are not detoxicated by these enzymes due to steric hindrance, but stilbene epoxide is a good substrate that is frequently used in experimental studies of these enzymes. 

A detailed study has been made of the base-catalysed deoxygenation of carbonyl compounds with diphenylphosphine oxide (52) at high temperatures. The known formation of good yields of frun -stilbene (56a) from benzaldehyde (53a) has been shown to involve the intermediate formation of cis- and mw5-stilbene epoxides, and their subsequent deoxygenation by (52). Similar deoxygenation of benzoylferrocene (53b) results in the formation of the ketones (54) and (55), as well as the hydrocarbons (56b) and (57). The rationalization given in Scheme 9 has been presented to explain these observations. ... 

The addition of aldehydes to carb - rCHN, to form stilbene epoxides prepared from 10-mercaptoisobc Jes derived from 48 on aldehydes i - -nciple underlies a synthesis of chn... 

The addition of aldehydes to carbenoids derived from the Cu-catalyzed decomposition of ArCHNj to form stilbene epoxides is subject to asymmetric induction by 1,3-oxathiane 47 prepared from 10-mercaptoisobomeol and acetaldehyde. The attack of sulfonium ylides derived from 48 on aldehydes also affords epoxides of high optical purity. The same principle underlies a synthesis of chiral aziridines. ... 

In order to characterize the nature of the oxygenating species formed in the reactions of H2O2, PhIO, MCPBA, and dioxygen plus aldehyde, we studied stereoselectivity in c/5-stilbene epoxidation, regioselectivity in (+)-limonene and norbornene epoxidations, and intermolecular competitive reactions between cyclohexene... 

This formation was linear as a function of time and cyclohexanol was only detected as a very minor product. Cyclooctane was similarly oxidized with the formation of cyclooctanone as a major product. Other iron(III)porphyrins involving different axial ligands, like Fe(TDCPP)Q and Fe(TPP)Cl, were much less efficient and less selective. Irradiation of Fe(TDCPP)OH in the presence of 02 and cis-stilbene failed to give any formation of stilbene epoxide, and cyclohexene was mainly oxidized on its allylic position with formation of cyclohex-2-enol and cyclohex-2-enone under such conditions. Finally, the intermediate formation of OH radicals was detected by spin trapping experiments during cyclohexane oxidation by 02 with photochemically-activated Fe(TDCPP)OH. 

The site-isolated Ru complex (I) exhibited significant activity for alkene epoxidation using IBA and O2 for catalyst activation [23]. The homogeneous Ru precursor complex (G) lost its activity in the reaction mixture for trons-stilbene epoxidation, whereas the Si02-supported Ru complex (I) was active under similar... 

Mn(TPP)Cl Ascorbate Cyclohexenol Styrene Styrene oxide Cyclohexene, Epoxide CIS and trans stilbenes, Epoxides CIS- and trans-2-hexenes, Epoxides 2,3-Dimethyl-2-butene, Epoxides [83]... 

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