Trans- stilbene oxide

The effect of substrate structure on product profile is further illustrated by the reactions of cis- and trons-stilbene oxides 79 and 83 with lithium diethylamide (Scheme 5.17) [32]. Lithiated cis-stilbene oxide 80 rearranges to enolate 81, which gives ketone 82 after protic workup, whereas with lithiated trans-stilbene oxide 84, phenyl group migration results in enolate 85 and hence aldehyde 86 on workup. Triphenylethylene oxide 87 underwent efficient isomerization to ketone 90 [32]. 

The observation that addition of imidazoles and carboxylic acids significantly improved the epoxidation reaction resulted in the development of Mn-porphyrin complexes containing these groups covalently linked to the porphyrin platform as attached pendant arms (11) [63]. When these catalysts were employed in the epoxidation of simple olefins with hydrogen peroxide, enhanced oxidation rates were obtained in combination with perfect product selectivity (Table 6.6, Entry 3). In contrast with epoxidations catalyzed by other metals, the Mn-porphyrin system yields products with scrambled stereochemistry the epoxidation of cis-stilbene with Mn(TPP)Cl (TPP = tetraphenylporphyrin) and iodosylbenzene, for example, generated cis- and trans-stilbene oxide in a ratio of 35 65. The low stereospecificity was improved by use of heterocyclic additives such as pyridines or imidazoles. The epoxidation system, with hydrogen peroxide as terminal oxidant, was reported to be stereospecific for ris-olefins, whereas trans-olefins are poor substrates with these catalysts. 

Phenobarbital, trans stilbene oxide, 2-acetyl aminofluorene Various, including phenobarbital... 

Mn impregnated into MCM-4i, a silicalite containing uniform mesopores of approximately 22 A, catalyzes TBHP epoxidation of alkenes.88 Over Mn-MCM-41, both cis- and trans-stilbene yield trans-stilbene oxide, which the authors conclude signals a radical mechanism.88 In contrast, over Ti—MCM-41, trans-stilbene cannot be oxidized, only cis-stilbene is epoxidized to the cis-stilbene oxide, which suggest a radical-free mechanism.89 Finally, emphasizing the shape selectivity possibilities, only trans-stilbene (not cis-stilbene) can be epoxidized over Mn-ZSM-5, a zeolite with relatively small pores of 5.1 x 5.4 A (Fig. 6.14).88... 

Rearrangement of trans-Stilbene Oxide to Diphenylacetaldehyde with Catalytic Methylaluminum Bis(4-bromo-2,6-di-tert-butylphenoxide). 

The checkers report that GLC analysis (Note 13) at this point shows that the product is contaminated with ca. 4% of trans-stilbene oxide and <1% of the Tischenko product (Note 14). 

Gas chromatography conditions are as follows Supelco fused silica capillary SPB-1 column (30 m, 0.32-mm ID, 0.25 micrometers df), 100°C initial temperature, 280°C final temperature, 10°C/min. The following retention times were obtained diphenylacetaldehyde (6.7 min), trans-stilbene oxide (7.4 min), Tischenko product (18.2 min). 

T. Ooi, K. Maruoka, and H. Yamamoto 95 REARRANGEMENT OF trans-STILBENE OXIDE TO DIPHENYL-ACETALDEHYDE WITH CATALYTIC METHYLALUMINUM BIS(4-BROMO-2,6-DI-tert-BUTYLPHENOXIDE)... 

Figure 2.10 Chromatograms of ( + )-trans-stilbene oxide. Conditions column, Chiralpak OP( + ), 25 cm x 4.6 mm i.d. eluent, methanol column temperature, ambient flow rate, 1 ml min -detector A, polarimeter B, refractive index.

The human cytosolic epoxide hydrolase (cytosolic EH, cEH, also known as soluble EH) has 554 amino acids (Mr 62.3 kDa) and is the product of the EPHX2 gene [49]. Its specific substrate is trans-stilbene oxide, and it appears... 

Fig. 10.28. The stereochemistry of enzymatic hydrolysis of stilbene oxide. The achiral (meso) r/.v-sli Ibene oxide (10.7) yields only one of the two enantiomers of IhreoA,2-diphcnylethane-1,2-diol (10.122). In contrast, the chiral trans-stilbene oxide (10.121) is hydrated exclusively to meso-l -diphenylethane-l -diol [182][183]. 

The chiral substrate trans- stilbene oxide (10.121) behaved differently, yielding meso-l,2-diphenylethane-l,2-diol (meso-10.122) [183], This means that, in both enantiomeric substrates, the enzyme does not discriminate between the two oxirane C-atoms, bringing about inversion of configuration at the C-atom attacked. Interestingly, the various stereoisomers of 1,2-diphenylethane-l, 2-diol can be interconverted metabolically by alcohol/ketone equilibria catalyzed by alcohol dehydrogenases. 

Table 8 Recycling data of catalyst 67 for AKR of trans stilbene oxide using aniline as...

We have previously reported that when the rearrangement of trans-stilbene oxide was carried out with CF3SO3H, the solution turned red and the product diphenylacetaldehyde was less pure than that obtained with bismuth triflate. This observation points to the role of bismuth(III) triflate as a Lewis acid in the rearrangement of epoxides and not to protic acid catalysis by triflic acid released by hydrolysis of bismuth triflate. 

Stereoselectivity is also observed in the oxidation of stilbens with the zeolite-entrapped t-butyl substituted FePc catalyst. With the cis-stilben as substrate the ratio of trans to cis product (trans-stilben is produced via the epoxidation of cis-stilben)is remarkably higher for FePc(t-Bu)4/NaY, compared with those for FePc(t-Bu)4+NaY and even for FePc/NaY and FePc+NaY samples under the similar conditions, as shown in Table 2. It was found that the stereoselectivities toward trans-products (trans-stilben + trans-stilben oxide) kept remained(48-53% sel) for the different conversions of cis-stilben. The... 

The specific development of a batch process is illustrated in the following example, namely the separation of the enantiomers of racemic trans-stilbene oxide (TSO) [28], For this example, supercritical fluid chromatography was particularly appropriate for the resolution. 

X Y Yield (%) cis-trans- cis-trans-Stilbene oxide Stilbene ... 

Mnm(Por)X also catalyze oxygen transfer from iodosobenzene to hydrocarbons.12 The reactions are apparently stepwise, for example, cyclohexane hydroxylation accompanies halogenation by the counterion X, and cis-stilbene gives a mixture of cis- and trans-stilbene oxide (1.6 1). The active species is proposed to be O—Mnv(Por)X. 

Benzoin, methylbenzoin, ethylbenzoin, isopropylbenzoin, benzoin oxime, cyclobutyldianilide carbamate, 1,1 -binaphthyl-2,2 -diol, trans-stilbene oxide, and Trogers s base Polymethacrylate 104, 96... 

J. Seidegard, R.W. Pero, The Hereditary Transmission of High Glutathione Transferase Activity towards trans-Stilbene Oxide in Human Mononuclear Leukocytes , Human Genet., 69, 66-68 (1985). 

Lynam and Nicolas have evaluated chiral separations by HPLC versus SFC [14] The enantiomers studied were pharmaceutical synthetic precursors. Repeated injections of trans-stilbene oxide and carbobenzyloxy phe-nylalaninol were made and the chromatographic parameters Rs, N, and a were calculated daily. SFC gave superior enentiomeric resolution of peaks and there was a faster solvent equilibration. The columns were quite stable in both SFC and HPLC systems. 

Fig. 10.1 Selected chiral sulfides and results obtained using alkylation/ deprotonation catalytic methodology for the asymmetric synthesis of trans-stilbene oxide, dr = trans cis solvents and additives vary.

E-Stilbene (0.181 g, 1 mmol) was dissolved in 1 2 acetonitrile DMM (15 mL). To this solution were added buffer (10 mL, 0.05 M solution of Na2B4O7l0H2O in 4 x 10-4 M aqueous Na2(EDTA)), tetrabutylammonium hydrogen sulfate (0.015 g, 0.04 mmol), and ketone catalyst (77.4 mg, 0.3 mmol). The mixture was cooled in an ice bath. A solution of Oxone (0.85 g, 1.38 mmol) in aqueous Na2(EDTA) (4 x 10-4 M, 6.5 mL) and a solution of K2CO3 (0.8 g, 5.8 mmol) in water (6.5 mL) were added dropwise separately over a period of 1.5 h (via syringe pumps or addition funnels). The best results were obtained if these solutions were added in a steady, uniform manner. After 2 h, the reaction was diluted with water (30 mL), and extracted with hexanes (4 x 40 mL). The combined extracts were washed with brine, dried (Na2S04), filtered, concentrated, and purified by FC on silica gel (previously buffered with 1% triethylamine solution in hexane) using 1 0 to 50 1 hexane ether as eluent. This provided trans-stilbene oxide (0.153 g, 78%) with 98.9% ee. 

Capillaries packed with poly-A-acryloyl-L-phenylalanine ethyl ester (Chiraspher) modified silica were used for electrochromatographic enantiomer separation of ben-droflumethiazide. To suppress bubble formation, the inlet buffer vial was pressurized to 12 bar and the outlet buffer vial to 4 bar [42], Acetonitrile or methanol were used as organic modifier whereby acetonitrile was superior to methanol. Non-aqueous p-CEC was performed on helical poly(diphenyl-2-pyridylmethylmethacrylate) coated on wide-pore aminopropyl silica [56]. With this chiral stationary phase, the enantiomer separation of Trogers base, benzoin acetate, methylbenzoin and trans-stilbene oxide was achieved by pressure-supported CEC, applying a higher pressure to the inlet than to the outlet buffer vial. 

Several ruthenium complexes bearing chiral Schiff s base ligands have been published. RuL(PPh3)(H20)2], complex C (Fig. 11), with PhIO produced (S)-styrene oxide in 80% ee [61]. Chiral Schiff s base complex D was examined using molecular oxygen with aldehyde, with or without 2,6-dichloropyridine N-oxide as an axial ligand. Styrene oxide was produced in up to 24% ee[62]. A chiral bis(oxazolinyl)pyridine ruthenium complex E with iodosylbenzene diacetate PhI(OAc)2 produced (lS,2S)-fra s-stilbene oxide in 74% ee [63]. Similarly, chiral ruthenium bis(bipyridine) sulfoxide complex F [64] was effective in combination with PhI(OAc)2 as an oxidant and resulted in in 33% ee for (R,R) trans-stilbene oxide and 94% ee for (R,R) trans-/i-Me-styrene (after 75 h at 25 °C). 

SYNTHESIS OF EPOXIDES USING DIMETHYLDIOXIRANE trans-STILBENE OXIDE... 

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