• Bulletin of the Korean Chemical Society
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• v.30 no.10
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• pp.2217-2222
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• 2009

The transition structures for the epoxidations of ethylene and the disproportionations by the dioxiranes of phosphines, phosphites and sulfides were studied with density function theory methods using the Becke3LYP functional and 6-311+G(2d,p) basis set. When the dioxiranes have methyl substituents rather than hydrogen substituents, the reaction barriers ($E_{TS}$) become higher in their epoxidations of ethylene by the steric hindrance, but become lower in their disproportionations of phosphines, phosphites and sulfides, which indicates that the nature of the dioxiranes seems to be electrophilic and in their disproportionations the reaction barriers are effected both by the electrophilicity and the steric hindrance. The steric factors in the disproportionations were calculated and more bulky substituents at dioxiranes may be necessary to retard the disproportionation and to enhance the epoxidation.

• Korean Chemical Engineering Research
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• v.46 no.4
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• pp.665-668
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• 2008

Propylene epoxidation by $H_2O_2$ (30% aqueous) as oxidant was studied in a semi-batch reactor using Ti-MCM-22 catalyst: Effects of reaction temperature, pressure, catalyst loading, solvent, and $H_2O_2$ concentration on $H_2O_2$ conversion (limiting reagent) were investigated. Product inhibition by propylene oxide was confirmed. Ti-MCM-22 maintained virtually the same catalytic performance over the 5 repeated cycles.

• Elastomers and Composites
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• v.54 no.4
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• pp.286-293
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• 2019

In this study, flexible poly(ethylene-ter-1-hexene-ter-divinylbenzene) was prepared using four types of metallocene catalysts (rac-Et(Ind)₂ZrCl₂, rac-SiMe₂(Ind)₂ZrCl₂, rac-SiMe₂(2-Me-Ind)₂ZrCl₂, (C₅Me₅)TiCl₂[O-2,6-ⁱPr₂(C₆H₃)]) and two types of borate catalysts (trityl tetrakisborate and dimethylanilinium tetrakisborate). The yield, catalytic activity, molecular weight, structure, composition, and thermal properties of the terpolymers prepared using the various catalysts and cocatalyst systems were evaluated. Epoxidation of the terpolymers was successfully performed and this transformation was studied by ¹H NMR and FTIR.

• Bulletin of the Korean Chemical Society
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• v.28 no.11
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• pp.2051-2055
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• 2007

The solvent effect on sulfur ylide mediated epoxidation reaction was studied systematically. While higher trans/cis ratio of the epoxide was obtained in the more polar solvent, protic solvent produced the lower trans/ cis ratio than any aprotic solvent.

• Bulletin of the Korean Chemical Society
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• v.15 no.11
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• pp.957-961
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• 1994

Epoxidation of olefins catalyzed by iron-tetraarylporphyrins were studied to see the shape selectivity in the competing reaction between cis-and trans- or internal and external olefins. Cis-olefins were more reactive than trans-olefins in the competing reaction between cis-and trans-olefins. Interestingly, in the epoxidation of $cis-{\beta}-methystyrene$ by ${\alpha}{\beta}{\alpha}{\beta}$ atropisomer of Fe(III)TNPPPCl and iodosylbenzene, 27% of total product was phenylacetone. The unusually large amount of phenylacetone may be produced by hydride rearrangement of carbocationic intermediate. Regioselectivity of the reaction was also studied by using the most sterically hindered Fe(III)TTPPPCl. In the epoxidation of limonene with Fe(III)TTPPPCl, the disubstituted double bond was more reactive than trisubstituted double bond. This is in contrast to the results obtained with other iron-tetraarylporphyrins. Similar trend was also observed in the competing reaction between mono-and di-substituted olefins.

• YAKHAK HOEJI
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• v.30 no.6
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• pp.329-333
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• 1986

6-[3-(Hydroxymethyl)-2, 3-epoxybutyl]-3, 5-dimethoxyphenol was synthesized by means of the eight steps, such as allylether, Claissen rearrangement, tosylation, oxidation, Wittig reaction, reduction and epoxidation from 3, 5-dimethoxyphenol. The epoxidation of 6-[3- (hydroxymethyl)-2-butenyl]-3,5-dimethoxy phenol using the L-(+)-diethyltartrate(DET), titanium (IV) isopropoxide Ti[(O-iPr)$_4$] and t-butylhydroperoxide(TBHP) is described.

• Archives of Pharmacal Research
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• v.17 no.4
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• pp.249-255
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• 1994

An efficient synthetic method for 11-deoxyanthracycline AB synthons is described. A verstile key intemediate vinyl bromide 3 was prepared from 5- methodxy-1-tetralone in three steps, and then was converted to the allylic alcohols 4 and 8 which, in tum, fumished highly fuctionalized AB synthons 7 and 12, respectively, via sequential epoxidation-reduction-protection processes.

• Bulletin of the Korean Chemical Society
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• v.29 no.4
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• pp.866-868
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• 2008

• Proceedings of the PSK Conference
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• 2003.10b
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• pp.184.2-184.2
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• 2003

Many naturally occurring polyhydroxylated sterols and oxysterols exhibit potent biologic activities. The role of oxycholesterol including 2, 5(R)-2, 6-hydroxycholesterol is a potent inhibitor of cholesterol biosynthesis in vitro as it is an effective inhibitor of HMG-Coa reductase. Some new polyhydroxylated sterols were showed potent cytotoxicity to cancer cells. And it has also been chown to be an inhibitor of DNA synthesis, In order to synthesize the various oxy derivatives, we tried to positionselective and reagentselective epoxidation and reduction of cholesterol derivatives. (omitted)

• Toxicological Research
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• v.15 no.1
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• pp.95-101
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• 1999

Cytochrome P450 (CYP) 3A4 metabolizes aflatoxin B1 (AFB1) to AFB1-exo-8,9-epoxide (8,9-epoxidation) and aflatoxin Q1 (AFQ1; 3$\alpha$-hydroxylation) simultaneously. We investigated whether each metabolite was formed via its own binding site of CAP3A4 active site. Kinetics of the formation of the two metabolites were sigmoidal and consistent with the kinetics of substrate activation. The HIll model predicted that two substrate binding wites are involved in the oxidationof AFB1 by CYP3A4. Dehydronifedipine, a metabolite of nifedipine generated by CYP3A4, inhibited the formation of AFQ1 without any inhibition in the formation of AFB1-exo-8,9-epoxidation. Dehydronifedipine was found to act as a reversible competitive inhibitor against 3$\alpha$-hydroxylation of AFB1. Vmax and S0.5 of the 8,9-epoxidation were not changed in the presence of 0, 50, or 100 $\mu\textrm{M}$ dehydronifedipine. S0.5 of 3$\alpha$-hydroxylation was increased from 58$\pm$4 $\mu\textrm{M}$ to 111$\pm$8 $\mu\textrm{M}$ in the presence of 100 $\mu\textrm{M}$ nifedipine whereas Vmax was not changed. These results suggest that there exist two independent binding sites in the active site of CAP3A4 . One binding site is responsible for AFB1-exo-8,9-epoxidation and the other is involved in 3$\alpha$-hydroxylation of AFB1. Dehydronifedipine might selectively bind to the site which is responsible for the formation of AFQ1 in the active site of CYP3A4.