Photochemical reactions epoxidation

Enantioselective rearrangement of epoxides to allylic alcohols 91TA1. Photochemical reactions of glycidyl esters 92MI11. 

The authors [23] applied the method of density fimctional (exchange-correlation functional B3LYP) and calculated the profdes of the potential energy for the interaction of ozone with ethylene. It was shown that, according to the scheme of ozonolysis of ethylene, the reaction pathway through the direct epoxidation of the double C=C bond requires high energy of activation and is improbable, both for thermochemical and photochemical reactions of ozonolysis. 

Different techniques have been used to study the products of photoreactions of organometallic compounds for example, irradiation of the arene complexes [CpFe() -arene)]+ resulted in the substitution of the arene by solvent or other potential ligands present in solution. In solutions containing an epoxide monomer, this photochemical reaction generated a species that initiated polymerization. Ion cyclotron resonance Fourier transform mass spectrometry and electrospray ionization mass spectrometry were used to elucidate the mechanism of these photoinitiated polymerizations. 

Thermal and Photochemical Reactions of Oxirans. - Isotopic labelling has been used to prove that the thermal rearrangement of phenyloxiran proceeds via a 1,2-shift of hydrogen, and not phenyl migration (Scheme 13). The epoxide (202), labelled with at C-2, gives entirely C(2)-labelled phenyl-ethanol (203) and 3,3- H2-labelled (202) gives (203) with at both C-1 and C-2. The method does not, however, distinguish between the transfer of H and of H. ... 

A study of the photochemical reactions of the isomeric steroidal epoxides (123) has shown that the main reaction is fission of the — bond to produce the... 

The vapor-pheise photochemical reaction of chlorine dioxide with ethylene was observed by Furst (65) to give chloroacetic acid. Leopold and Mutton (137) discovered that the reaction between triolein and chlorine dioxide is accelerated by light cind gives a mixture of products, containing carbonyl, hydroj l, euid epoxide groups, as well as chlorine. CSilorine dioxide oxidations carried out by Lindgren and co-workers on cyclohexene (143) and methyl oleate (142) in the cib-sence of special illumination showed only a little... 

Miscellaneous Methods. Epoxides may be synthesized by both thermal and photochemical reactions of 1,2-dioxolans. Thus pyrolysis of 3,3,5,5-tetrasub-stituted 1,2-dioxolans (152) occurs via a biradical intermediate in the formation of epoxides (153) and ketones. The ratio of epoxide to ketone products... 

Epoxides.—Reviews on aspects of epoxide transformation which have appeared include catalytic hydrogenation, photochemical reactions, stereoselective cleavage, and basic epoxide behaviour in the presence of halide ions. ... 

Photochemical Reactions Leading to Epoxides or Oxidoannulenes of C lCjo... 

In contrast to the commonly observed, highly selective photochemical reactions, thermal rearrangements of endoperoxides often lead to more complex mixturex of products.A naturally occurring compound, the terpene endoperoxide ascaridole (3a) rearranges into isoascaridole (4a) upon irradiation (long-wavelength excitation at 366 nm) while similar cyclohexadiene endoperoxides 3 result in mixtures of bis-epoxides 4 and epoxyketones 5 upon thermolysis (Scheme 5). ... 

While the photochemical reaction proceeds stereospecifi-cally, the thermal process between Fe(CO)5 and vinyl epoxides... 

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... 

For example, diethylamine sensitizes the photodegradation of DDT to yield DDE, TDE, dichlorobenzophenone, and two other unidentified compounds (6).. These reactions are thought to involve a charge transfer from the amine to DDT. Similarly, rotenone is highly effective in enhancing the photochemical alteration of dieldrin to photodieldrin ( 7). Rotenone also catalyzes the photochemical alteration of aldrin, isodrin, endrin, heptachlor, and heptachlor epoxide but it is less effective or ineffective with DDT, DDE, lindane, and endosulfan (7, 8). 

CgoO (1) can also be prepared by allowing toluene solutions of CgQ to react with dimethyldioxirane (Scheme 8.3) [28], The so-obtained product is identical to that prepared by photochemical epoxidation [15], Upon treatment of CgQ with dimethyldioxirane, a second product is formed simultaneously (Scheme 8.3), which was identified to be the 1,3-dioxolane 6. Upon heating 6 in toluene for 24 h at 110 °C, no decomposition could be observed by HPLC, implying that 1 and 6 are formed by different pathways. Replacement of dimethyldioxirane with the more reactive methyl(trifluoromethyl)dioxirane allows much milder reaction conditions [29]. At 0 °C and a reaction time of only some minutes this reaction renders a CgQ conversion rate of more than 90% and higher yields for CgoO as well as for the higher oxides. 

The formation of the oxepin is reasonably explained by an electrocyclic ring opening of rearranged epoxide 299 in a thermal reaction. As mentioned above, two routes to 299 are possible. If the rearrangement is concerted, a 1,5-sigmatropic reaction with inversion of the reaction center (oxygen) in 299 is photochemically allowed. It is possible to separate a nonconcerted process... 

The epoxide is also formed from the reaction of C60 with dimethyldioxirane, and the 1,3-dioxolane (figure 9) is also obtained (Elemes et al. 1992). Photochemical irradiation of C60 in hexane had previously been shown to result in the addition of 2-5 oxygens, and also various methylene groups (the results depend upon the fullerene purity) (Wood et al. 1991). In this work, two oxygens were found to add to C70. 

---