Epoxide formation in the reaction

Skov, H Th. Benter, R. N. Schindler, J. Hjorth, and G. Restelli, Epoxide Formation in the Reactions of the Nitrate Radical with 2,3-Dimethyl-2-butene, cis- and trans-2-Butene, and Isoprene, Atmos. Environ., 28, 1583-1592 (1994). 

H. Skov, Th. Benter, R.N. Schindler, J. Hjorth, G. Restelli Epoxide formation in the reactions of the nitrate radical with 2,3-dimethyl-2-butene, cis- and rran5-2-butene and isoprene, Atmoj. Environ. 28A (1994) 1583. 

A REMPI-study of NO3 and epoxide formation in the reaction of styrene with NO3 radicals at low pressure,... 

Epoxide formation in the reactions of nitrate radical with 2,3-2-dimethyl-2-butene, cis- and trans-2-butQn and isoprene,... 

Aliphatic Epoxidation. Many aliphatic and alicylcic compounds containing unsaturated carbon atoms are thought to be metabolized to epoxide intermediates (Figure 7.4). In the case of aldrin the product, dieldrin, is an extremely stable epoxide and represents the principle residue found in animals exposed to aldrin. Epoxide formation in the case of aflatoxin is believed to be the final step in formation of the ultimate carcinogenic species and is, therefore, an activation reaction. 

The basic permanganate oxidation of conjugated 1,3-dienes is different from those reported for the 1,4-dienes above. Therefore, in the oxidation of cyclopentadiene and 1,3-cyclohexadiene (13) a mixture of five products 14-18 is obtained (equation 4) . In this reaction 14 and 16 are derived from the normal cis hydroxy la tions whereas 17 and 18 were said to be formed from 15 by hydration in what the authors term an epoxidic pathway. Formation of epoxy-diols under similar permanganate oxidations has been found for occidentalol (19), levopimaric acid (20) and a 1-chloro- or 1-bromo-l,3-diene (21) as an intermediate step in the synthesis of (+)-D-c/tfrc-3-inosose and (+)-D-c/r/ro-3-inositol (equation 5). The explanation for the epoxide formation in the oxidation of 1,3-dienes (13, 19-21) is not clear but may be connected to the fact that other additions of permanganate to dienes are possible beyond those commonly observed... 

In terms of cost, the effectiveness of the catalytic cycle in the ring closure makes this process economical in palladium. The first three steps in the reaction sequence -- ring opening of an epoxide by a Grignard reagent, converison of an alcohol to an amine with inversion, and sulfonamide formation from the amine — are all standard synthetic processes. 

In general, thiocyanate salts are used for the epoxide-thiirane conversions. The reaction proceeds by nucleophilic attack on the epoxide by thiocyanate ion followed by cyclization as shown for (121) (125). The formation of a... 

By studying the NMR spectra of the products, Jensen and co-workers were able to establish that the alkylation of (the presumed) [Co (DMG)2py] in methanol by cyclohexene oxide and by various substituted cyclohexyl bromides and tosylates occurred primarily with inversion of configuration at carbon i.e., by an 8 2 mechanism. A small amount of a second isomer, which must have been formed by another minor pathway, was observed in one case (95). Both the alkylation of [Co (DMG)2py] by asymmetric epoxides 129, 142) and the reduction of epoxides to alcohols by cobalt cyanide complexes 105, 103) show preferential formation of one isomer. In addition, the ratio of ketone to alcohol obtained in the reaction of epoxides with [Co(CN)5H] increases with pH and this has been ascribed to differing reactions with the hydride (reduction to alcohol) and Co(I) (isomerization to ketone) 103) (see also Section VII,C). 

The pH-dependence of the inactivation rate indicated the participation of both a basic and an acidic group in the reaction with 40. The latter could be explained by the formation at the active site of the highly reactive epoxide 1,2-anhydroconduritol F (42) which is subsequently activated by the acidic... 

In order to rationalize the complex reaction mixtures in these slurry reactions the authors suggested that irradiations of the oxygen CT complexes resulted in simultaneous formation of an epoxide and dioxetane36 (Fig. 34). The epoxide products were isolated only when pyridine was co-included in the zeolite during the reaction. Collapse of the 1,1-diarylethylene radical cation superoxide ion pair provides a reasonable explanation for the formation of the dioxetane, however, epoxide formation is more difficult to rationalize. However, we do point out that photochemical formation of oxygen atoms has previously been observed in other systems.141 All the other products were formed either thermally or photochemically from these two primary photoproducts (Fig. 34). The thermal (acid catalyzed) formation of 1,1-diphenylacetaldehyde from the epoxide during photooxygenation of 30 (Fig. 34) was independently verified by addition of an authentic sample of the epoxide to NaY. The formation of diphenylmethane in the reaction of 30 but not 31 is also consistent with the well-established facile (at 254 nm but not 366 or 420 nm) Norrish Type I... 

When the ketone (280) was heated at reflux with pTsOH in benzene, the product (281) was isolated 95). The mechanism of this intriguing rearrangement may involve 1,3-hydride shift or epoxide formation 9S), This reaction appears to be an efficient method for the synthetis of [3.3.3]propellane. 

One can easily envisage the formation of stereochemically enriched materials by an asymmetric version if the methodology developed by Jacobsen et al. <2000ACR421> of epoxide ring-opening reactions with azides is applied in the reaction sequence. 

Aluminum porphyrins with alkoxide, carboxylate, or enolate can also activate CO2, some catalytically. For example, Al(TPP)OMe (prepared from Al(TPP)Et with methanol) can bring about the catalytic formation of cyclic carbonate or polycarbonate from CO2 and epoxide [Eq. (6)], ° - and Al(TPP)OAc catalyzes the formation of carbamic esters from CO2, dialkylamines, and epoxide. Neither of the reactions requires activation by visible light, in contrast to the reactions involving the alkylaluminum precursors. Another key difference is that the ethyl group in Al(TPP)Et remains in the propionate product after CO2 insertion, whereas the methoxide or acetate precursors in the other reactions do not, indicating that quite different mechanisms are possibly operating in these processes. Most of this chemistry has been followed via spectroscopic (IR and H NMR) observation of the aluminum porphyrin species, and by organic product analysis, and relatively little is known about the details of the CO2 activation steps. 

Epoxytrichloroacetimidates 153 also undergo oxazoline ring formation in the presence of a catalytic amount of Lewis acids.Diethylaluminum chloride was found to be superior to boron trifluoride, which tends to further hydrolyze the oxazoline 154 to the trichloroacetamide. Generally, formation of the six-membered ring oxazine 155 is not favored, but it can be a serious side reaction if the epoxide contains substituents that stabilize the incipient cation generated prior to ring closure. Examples from this study are summarized in Table 8 19 (Fig 8 8 Scheme 8.45). 

The total yields from epoxidation are in the range of 35-90. The rate of the reaction with peroxy acids is rather low one to seven days are usually necessary for completion of epoxide formation. 

Epoxidaiion of HPL. Results from the epoxidation of HPL with ECH in the presence of KOH and QAS using methylene chloride (at room temperature) as solvent are shown in Figure 3. The degree of conversion of (aliphatic) hydroxy groups of HPL to epoxide functionality was monitored by titration. Parameters important to the success of this reaction included (a) stepwise addition of KOH, approximately paralleling the formation of KC1 by dechlorohydrogenation (b) presence of QAS in the reaction mixture (c) an at least five-fold stoichiometric excess of ECH over available... 

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