Monoepoxidation

Regioselective 1,4-azidohydroxylation to give 309 takes place by the reaction of the vinyloxirane 308 with sodium azide[188]. The reaction of the cyclopen-tadiene monoepoxide 310 with sodium azide or purine base offers a good synthetic method for the carbocyclic nucleoside 311(189-191]... 

Carboxylate anions are better nucleophiles for allylation. The monoepoxide of cyclopentadiene 343 is attacked by AcOH regio- and stereoselectively via tt-aliylpalladium complex formation to give the m-3,5-disubstituted cyclopen-tene 344[212]. The attacks of both the Pd and the acetoxy anion proceed by inversion (overall retention) to give the cis product. 

Butadiene can also be readily epoxidized with peracids to the monoepoxide or the diepoxide (109,110). These have been proposed as important intermediates in the metaboHc cycle of butadiene in the human body (111). 

Exposure studies have been made using mice and rats (257). These experiments have demonstrated species differences in butadiene toxicity and carcinogenicity. Butadiene was found to be a potent carcinogen in the mouse, but only a weak carcinogen in the rat. The interpretations have focused on differences in toxification rates and detoxification metaboHsms as causative factors (257). The metaboHsm is beHeved to proceed through intermediates involving butadiene monoepoxide and butadiene diepoxide (257). A similar mechanism has been proposed for its biodegradation pathway (258). 

The stereospecific polymerization of alkenes is catalyzed by coordination compounds such as Ziegler-Natta catalysts, which are heterogeneous TiCl —AI alkyl complexes. Cobalt carbonyl is a catalyst for the polymerization of monoepoxides several rhodium and iridium coordination compounds... 

Rearrangements are also observed during halojluonnanons with cyclic medium ring dienes [70, 93] (equations 4 and 5) and with the monoepoxide of 1,5-cyclooctadiene [94] (equation 6) during halofluonnations Again, there are differences in product mixture with apparently minor variations in reagents (equation 4)... 

Oxidative reactions of dienes are accomphshed under similar conditions as those of alkenes. Abicydic diene synthesized from hexafluorobenzene and 1,2-di-chloroethylene is monoepoxidized by triflnoroperoxyacetic acid [43] (equation 35). 

Nonconjugated perfluorocyclohepta-l,4-diene is oxidized to the corresponding diepoxide by sodium hypobromite [17] (equation 36), whereas the conjugated- 1,3-diene gives a mixture of 1,2-monoepoxide and bridged 2,3 1,4-diepox-ide [IT] (equation 36). 

Epoxidation of norbornene was found some time prior to this work not to stop at the monoepoxide step. Instead, this intermediate goes on to rearrange to the bicyclic aldehyde, 31, ... 

Dibromo-7-oxabicyclo[4.1.0]heptanes can be obtained by bromination of the respective 7-oxabicyclo[4.1.0]hept-3-ene, the monoepoxide of cyclohcxa-1,4-diene, and when submitted directly to the dehydrohalogenation reaction give products 3 and 4.2 149 150... 

The parent system oxonin (1) is generated by benzophenone sensitized irradiation with a Hanovia light source3 5 or direct irradiation6 of the monoepoxide of cyclooctatetraene (9-oxabicyclo[6.1.0]nona-2,4,6-triene, 6). 

The Gabriel synthesis represents another indirect but highly valuable approach to amines. Trost has demonstrated a method for the asymmetric ring-opening of butadiene monoepoxide by use of one equivalent of phthalimide, 7t-allylpalladium chloride dimer, and the chiral bisphosphine 22 (Scheme 7.37). The dynamic kinetic asymmetric transformation proceeded through a putative achiral intermedi-... 

Lindo-rv.ff oselecli ve oxacydization of polyepoxides is less common the first ster-eospedfic tandem endo-regioselective biomimetic oxacydization of polyepoxides to fused THP rings has only recently been reported [38a], The cyclization of the hydroxy-methoxymethyl-substituted triepoxide 75 (a 1,4,7-triepoxide), promoted and directed by La(OTf)3 through an intramolecular chelation and based on a procedure originally described for a monoepoxide system [38b], afforded the tri-... 

The catalytic system was subsequently applied to the monoepoxidation of dienes. This was potentially a difficult task, as there was a need to address the issues not only of enantioselectivity, but also of regioselectivity and monoepoxidation versus bisepoxidation. Fortunately, a wide range of dienes could be efficiently monoepoxidized by ketone 1, which meant that a straightforward route to vinylepoxides had been developed (Table 9.1) [9]. 

Table 9.1 A selection of dienes that could be monoepoxidized.

Cu(i(-catalyzed kinetic resolutions of racemic, cyclic 1,3-diene monoepoxides through the use of dialkylzinc [123] or trialkylaluminium reagents [124] have re-... 

As described in the preceding paragraphs, oxidation products of carotenoids can be formed in vitro as a result of their antioxidant or prooxidant actions or after their autoxidation by molecular oxygen. They can also be found in nature, possibly as metabolites of carotenoids. Frequently encountered products are the monoepoxide in 5,6- or 5, 6 -positions and the diepoxide in 5,6 5, 6 positions or rearrangement products creating furanoid cycles in the 5,8 or 5, 8 positions and 5,8 5, 8 positions, respectively. Products like apo-carotenals and apo-carotenones issued from oxidative cleavages are also common oxidation products of carotenoids also found in nature. When the fission occurs on a cyclic bond, the C-40 carbon skeleton is retained and the products are called seco-carotenoids. 

These authors proposed a reaction mechanism with P-carotene monoepoxides and diepoxides as intermediates for volatile formation. 

The oxidation of P-carotene with potassium permanganate was described in a dichloromethane/ water reaction mixture (Rodriguez and Rodriguez-Amaya 2007). After 12 h, 20% of the carotenoid was still present. The products of the reaction were identified as apocarotenals (apo-8 - to apo-15-carotenal = retinal), semi-P-carotenone, monoepoxides, and hydroxy-p-carotene-5,8-epoxide. 

On a capillary GC analysis, the separation of positional isomers of epoxy compounds is generally well accomplished by a high polar column, such as DB-23, rather than by a low polar column, such as DB-1. For the positional isomers, a different elution order depending on the kinds of column has not been reported. In the case of two mono epoxides derived from Z6,Z9-dienes, 6,7-epoxides elute slightly faster than 9,10-epoxides [72,170],but the separation is insufficient even on the high polar column. Three monoepoxides derived from Z3,Z6,Z9-trienes elute in the order of 6,7-, 3,4-, and 9,10-epoxides [9]. The former two isomers are sufficiently separated on the high polar column, while the elution of the latter two isomers overlaps [71]. For each positional isomer of diepoxides derived from the Z3,Z6,Z9-trienes, two diastereomeric... 

Table 7 Enantiomeric separation of monoepoxides derived from Z3,Z6,Z9-trienes and Z6,Z9-dienes with aC17-C23 straight chain on chiral HPLC columns [75,76,179]... 

For imperfect epoxy-amine or polyoxypropylene-urethane networks (Mc=103-10 ), the front factor, A, in the rubber elasticity theories was always higher than the phantom value which may be due to a contribution by trapped entanglements. The crosslinking density of the networks was controlled by excess amine or hydroxyl groups, respectively, or by addition of monoepoxide. The reduced equilibrium moduli (equal to the concentration of elastically active network chains) of epoxy networks were the same in dry and swollen states and fitted equally well the theory with chemical contribution and A 1 or the phantom network value of A and a trapped entanglement contribution due to the similar shape of both contributions. For polyurethane networks from polyoxypro-pylene triol (M=2700), A 2 if only the chemical contribution was considered which could be explained by a trapped entanglement contribution. 

In this contribution, we report equilibrium modulus and sol fraction measurements on diepoxidet-monoepoxide-diamine networks and polyoxypropylene triol-diisocyanate networks and a comparison with calculated values. A practically zero (epoxides) or low (polyurethanes) Mooney-Rivlin constant C and a low and accounted for wastage of bonds in elastically inactive cycles are the advantages of the systems. Plots of reduced modulus against the gel fraction have been used, because they have been found to minimize the effect of EIC, incompleteness of the reaction, or possible errors in analytical characteristics (16-20). A full account of the work on epoxy and polyurethane networks including the statistical derivation of various structural parameters will be published separately elsewhere. 

Figure 1. Theoretical dependence of sol fraction w vs. molar ratio rA is 2[NH,]/ [epox] for epoxyamine networks containing varying fraction of epoxy groups in monoepoxide s. Final conversion of epoxy groups in mol percent indicated.

Figure 2. Theoretical curves for superimposed reduced moduli Gd /RT(mol/ cm 3) of epoxy-amine networks versus the gel fraction ws. Fraction of epoxy groups in monoepoxide is O, 0 , 0.2 A, 0.33 V, 0.5. Key O, , A, V, dry networks , A, , swollen networks value of front factor A indicated.

Epoxides will also participate in radical reactions and this usually results in ring opening of the epoxide. The addition of a radical derived from xanthate 38 to butadiene monoepoxide provides the addition product 39 in good yields as an E/Z mixture of olefins <06AG(I)6520>. This reaction presumably proceeds through the addition of the xanthate-derived radical to the olefin, which then opens the epoxide. 

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