Epoxidation photochemical

Davidson, S.R. and Wilkinson, S.A., electron-beam-induced polymerization of epoxides. J. Photochem. Photobiol. A Chem.,SS, 123-134 (1991). 

Among the more exotic methods which have been used for the direct epoxidation of steroid olefins are chromic acid, ozone, e.g., (84), and photochemical oxygenation. Ozone is useful for the epoxidation of the unreactive 8,9-olefin, but the results of the other unusual methods can usually be duplicated by the methods of epoxidation discussed above. 

Pyran-4-ones bear an obvious structural similarity to the all-carbon cyclohexadienones discussed above. However, the original studies of their photochemical behavior revealed only dimerization processes to produce a cage product resulting from two successive head-to-tail [2 + 2]-photocycloadditions (Scheme 29)54. Much later, small amounts of substituted furfural 121 were observed during the irradiation of 11955a. It was speculated that 121 could arise from bicyclic epoxide 120, an intermediate analogous to those formed in cyclohexadienone photochemistry. Subsequent reports noted that further irradiation of... 

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... 

Schaap, A.P., Siddiqui, S., Prasad, G., Palomino, E. and Sandison, M. (1985). The photochemical preparation of ozonides by electron-transfer photo-oxygenation of epoxides. Tetrahedron 41, 2229-2235... 

Khenkin, A.M. and Neumann, R. (2000). Aerobic photochemical oxidation in meso-porous Ti-MCM-41 epoxidation of alkenes and oxidation of sulfides. Catal. Lett. 68(1-2), 109-111... 

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). 

Graham RE, Burson KR, Hammer CF, et al. 1973. Photochemical decomposition of heptachlor epoxide. J Agric Food Chem 21 824-834. 

Bicyclopropylidene (1) readily reacted with photochemically generated singlet oxygen at 30-35°C to give spiro[2.3lhexan-4-one (203) and 7-oxadi-spiro [2.0.2.1]heptane (202) [104,1411. Bicyclopropylidene epoxide 202 can also be prepared by epoxidation of 1 with m-chloroperbenzoic acid in the presence of Na2C03 [141] or with KHSOs/acetone [74]. Bicyclopropylidene (1) was found to quench the fluorescence of 9,10-dicyanoanthracene [81]. 

Curing of epoxy resins can also be achieved by ring-opening polymerization of epoxide groups using either Lewis acids (including those generated photochemically) or Lewis bases (Sec. 7-2). 

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. 

A -3,4-cis-THC has now been found in Cannabis sativa (Phenotype III) other papers reporting the characterization of compounds from Cannabis sativa concern conclusive identification and synthesis of cannabinodiol, " which is known to result from the photochemical irradiation of cannabinol (Vol. 7, p. 51), and the identification of A -tetrahydrocannabinolic acid " and (+)-cannabitriol (263) " (263) and the corresponding C-2 ethyl ether may be epoxide-derived. " ... 

Brief mention may be made here, incidentally, of an interesting photochemical epoxide isomerization reported by Bodforafi18 to give -di ketones in email yield from several substituted bcnzalaoetophonone oxides, as shown in Eq. (483). 

Photochemically induced epoxidation of tetrafluoroethene by oxygen with improved yields (71-76%, conversion 21-62%) is achieved in the presence of radical generators such as tri-bromofluoromethane, 1,2-dibromotctrafluorocthane, ethyl nitrite or 1 H, /F,5//-octafluoropen-tyl nitrite.36 The oxidation of tetrafluoroethene with oxygen can also be catalyzed with bis(trifluoromethyl)diazene an undistillable viscous oil with peroxide composition is formed initially which can be quantitatively converted into carbonyl fluoride when heated.37-38... 

Photochemically induced epoxidation of tetrqfluaraethylene by oxygen with improved yields (71 1-76 3%, conversion, 21-62 3%) is achieved in the presence of radical generators such as tribromofluoromethane, 1,2-dibromotetra-fluoroethane, ethyl nitrite, or 2,2,3,3-tetrafluoropropyl mtnte f5] Tnfluoioacrylo-mtrile can be epoxidized by oxygen under pressure at elevated temperatures [6] (equation 4)... 

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