Epoxidation study

The results of model compound studies with three different types of epoxides, obtained in the presence and absence of ammonium perchlorate are shown in Figures 4, 5, and 6. The epoxide DER-332 shows a uniform rate of disappearance for the acid and epoxide species in this reaction. In the presence of ammonium perchlorate, the rate is increased, and a minimum of side reactions occur. Similar data but faster reaction rates are obtained with Epon X-801, but the consumption of epoxide species by side reactions is increased, particularly in the presence of ammonium perchlorate. On the other hand, the epoxide ERLA-0510 (Table IV), which contains a basic nitrogen, shows a reaction rate which is an order of magnitude greater than that for DER-332, accompanied by a substantial increase in side reactions. In the presence of ammonium perchlorate, the side reactions of ERLA-0510 predominate. In all probability, the side reactions of the multifunctional epoxides studied are homopolymerization. 

The previous assignment of stereochemistry to isolongifolene epoxide (149)66 has been confirmed by epoxidation studies with analogous substrates.67 It has also been concluded that the factors controlling the stereochemistry of epoxidation are the bicyclohepty moiety and the C-2/3 methyl group. 

H202 decomposition as well as cyclohexene epoxidation studied... 

The methanolysis, azidolysis, and aminolysis of epoxy benzyl ethers and epoxy alcohols have been reported <93JOCl22l>. All the epoxides studied showed a tendency toward C-3 selectivity when a Lewis-acidic metal cation (Li+, Mg2+, or Zn2+) was added to the reaction mixture, suggesting that the nucleophilic attack in these instances is chelation-controlled (Equation (11), and see Table 2). 

The epoxidation studies by Cheng and Scott on another fascinating hydrocarbon, corannulene, should also be mentioned here <94MI 104-01). The initial formation of corannulene monoepoxide can be observed spectroscopically however, the second epoxidation is about as fast as the first,... 

For acyclic allylic alcohols, very little a,p-unsaturated enone formation was observed besides epoxidation. Chemoselectivity was much less for cyclic allylic alcohols, for which oxidation of fhe allylic alcohol group competed significantly with epoxidation. In the case of 2-cyclohexenol as the substrate, the enone was even found to be the main product. A comparative sandwich POM-catalyzed epoxidation study of various (subsfifufed) cycloalkenols revealed that the enone versus epoxide chemoselectivity is controlled by the C=C-C-OH dihedral angle Ma in the allylic alcohol substrate. The more this dihedral angle deviates from fhe optimum C=C-C-OW dihedral angle otw for allylic acohol epoxidation, the more enone is formed (Fig. 16.5). 

Trlfluoromethanesulfonlc acid as an example of a Bronsted acid was a very active catalyst with styrene oxide, but was a poor catalyst for the butene oxide and cyclohexane oxide at room temperature. Tetrasulfone was the most active catalyst for epoxides studied. 

Graslund, A. and Jemstrom, B. (1989) DNA-cardnogen interaction covalent DNA-adducts of benzojajpyrene 7,8-dihydrodiol 9,10-epoxides studied by biochemical and biophysical techniques. (9. Rev. Biophys., 22, 1-37. 

The DTA curves of three catalyzed and uncatalyzed epoxides are given in Figure 7.49. The epoxides studied were Epon 1310 [tetraglycidyl ether or tetrakis (hydroxphenyl)ethane], Diepoxide AG-13E (bis-epoxydicyclopentyi ether or ethyleneglycol), and UC Endo isomer (dicyclopentadiene dioxide). AH the uncatalyzed epoxides, except the UC Endo isomers, exhibited exo-... 

Titanium complexes have been shown to be active for the synthesis of cyclic carbonates or either di- or trithiocarbonates from epoxides and either carbon dioxide or carbon disulfide (Scheme 5.6). Titanium-catalysed synthesis of cyclic carbonates has been recently reviewed by North and coworkers. Titanium-salen complexes find application as catalysts, in combination with tetrabutylammonium bromide or tributylamine, for the synthesis of di- or trithiocarbonates from epoxides and carbon disulfide. It is worth highlighting that the catalyst loading can be reduced to 0.5 mol%, although 1 mol% of catalyst was required in order to achieve quantitative yields. The catalyst system showed a preference for dithiocarbonate formation for most of the epoxides studied. 

This mechanism later received support from epoxidation studies on cholesteryl acetate [117]. 

The epoxidation of olefins does not appear at this time to involve radical intermediates in most systems, but epoxidation through two different spin states of the same complex has gained acceptance. " In some cases, side products imply that intermediates are present, but these intermediates have been concluded by Bruice to be carbocationic instead of radical. The carbocation would allow for Z/E isomerization and formation of oxidation products other than epoxides. " Studies on the epoxidations of an olefin attached to... 

The stereochemistry of epoxides generated by chiral dioxiranes provides the opportunity to further address the transition state. The dioxirane derived from 39 has two diastereomeric oxygens. The equatorial oxygen is likely to be sterically more accessible for the epoxidation. Our studies show that while the epoxidation of trans- and tri-substitued olefins with ketone 39 proceeds mainly through spiro A, planar B is also competing (Figure 3.5) [34, 35, 43-47, 49, 50, 59]. Spiro A and planar B give the opposite stereochemistry for the epoxide product, thus their competition will affect the ee obtained for epoxidation. Studies have shown that the extent of involvement of... 

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