Epoxidation conjugated diene

Active anions have been used so far with epoxies, but epoxidation can be obtained by other means, as long as the polymer contains double bonds. It is possible to react an epoxidized conjugated diene polymer with a white filler, forming chemical bonds between rubber and silica without using a coupling... 

Epoxide opening with nucleophiles occurs at the less substituted carbon atom of the oxlrane ting. Cataiytic hydrogenolysis yields the more substituted alcohol. The scheme below contains also an example for trons-dibromination of a C—C double bond followed by dehy-drobromination with strong base for overall conversion into a conjugated diene. The bicycKc tetraene then isomerizes spontaneously to the aromatic l,6-oxido[l0]annulene (E. Vogel, 1964). 

Epoxidation of conjugated dienes can be regioselective when one double bond is more electron-rich than the other otherwise mixtures of mono- and diepoxides will be obtained. When the alkene contains an adjacent stereocenter, the epoxidation can be diastereoselective [2]. Hydroxy groups can function as directing groups, causing the epoxidation to take place syn to the alcohol [2, 3]. 

Conjugated dienes can be epoxidized to provide vinylepoxides. Cyclic substrates react with Katsuki s catalyst to give vinylepoxides with high ees and moderate yields [17], whereas Jacobsen s catalyst gives good yields but moderate enantiose-lectivities [18]. Acyclic substrates were found to isomerize upon epoxidation (Z, )-conjugated dienes reacted selectively at the (Z)-alkene to give trans-vinylepoxides (Scheme 9.4a) [19]. This feature was utilized in the formal synthesis of leuko-triene A4 methyl ester (Scheme 9.4b) [19]. 

Cumulenes have also been prepared by treating alkynyl epoxides with boron trifluoride. 1,4 Elimination of BrC C=C—CBr has been used to prepare conjugated dienes (C=C—C=C). ... 

Studies conducted by Barenghi eta.1. (1990) and Lodge etal. (1993) independently have demonstrated the facile, multicomponent analysis of a wide range of PUFA-derived peroxidation products (e.g. conjugated dienes, epoxides and oxysterols) in samples of oxidized LDL by high-field H-NMR spectroscopy. Figure 1.9 shows the applications of this technique to the detection of cholesterol oxidation products (7-ketocholesterol and the 5a, 6a and 5/3,60-epoxides) in isolated samples of plasma LDL pretreated with added coppcr(Il) or an admixture of this metal ion with H2O2, an experiment conducted in the authors laboratories. 

Some derivatization methods mentioned in other sections of this review include chemical ionization by nitric oxide (MS) or epoxidation (MS), formation of jr-complexes for NMR (shift agents) etc. Also, the Diels-Alder reaction, which was mentioned several times as a tool for derivatization of conjugated dienes and polyenes, was extensively described and reviewed in the literature. 

Asymmetric monoepoxidation of conjugated dienes has been accomplished via (salen)Mn(III)-catalyzed [salen = A,Ar/-bis(salicylidene)ethylenediamine] oxidation. The reaction exhibits regioselectivity for attack at cis double bonds of cA.traws-conjugated dienes, and affords trans epoxides as the major products from cis olefins33. Thus, diene 14 gave optically active fraws-vinylepoxide 15 as the major product with 87% ee as shown in equation 16. 

Asymmetric epoxidation of conjugated dienes and enynes catalysed by the chiral man-ganese(EI) complex 232 give monoepoxides exclusively reactions of cw-enynes give /raw.v-alkynyl epoxides as the major products with a high level of asymmetric induction362. 

The selective epoxidation of dienes by CPO from C. jumago has been reported (Scheme 2.23) [275]. The methacrylate was a good substrate which showed two types of selectivity only the isolated double bond was epoxidized to produce the monoepoxide in 73% yield and the conjugated a, 3-unsaturated bond of the methacrylic acid moiety was untouched. It was suggested that conjugated terminal alkenes might... 

Vinyl epoxides 372 and 373 are converted to conjugated dienes 375 and 378 via the 7T-allyl intermediates 374 and 377. In other words, different protons are eliminated, depending on the structure to give either the cyclopentenone 376 or the dienyl alcohol 378. The unsaturated ketone 376 is an expected product, because elimination of a hydride from the carbon connected to oxygen is common [171]. 

Asymmetric Epoxidation of Representative Conjugated Dienes and Enynes by Ketone 1... 

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