Stilbene photooxygenation

In the presence of oxygen, electron transfer sensitization of t-1 or c-1 results in stilbene photooxygenation to yield... 

FIGURE 1.14 Photooxygenation of (a) 7,12-diniethylbenz[a]anthracene, (b) benzo[a]pyrene, and (c) photo-cylization of cw-stilbene. 

Takeya, H., Kuriyama, Y. and Kojima, M. (1998). Photooxygenation of stilbenes in zeolite by excitation of their contact charge transfer complexes with oxygen. Tetrahedron Lett. 39, 5967-5970... 

Phosphoryl-stabilized anions, 25, 2 Photochemical cycloadditions, 44, 2 Photocyclization of stilbenes, 30, 1 Photooxygenation of olefins, 20, 2 Photosensitizers, 20, 2 Pictet-Spengler reaction, 6, 3 Pig liver esterase, 37, 1 Polonovski reaction, 39, 2... 

In the solution phase, cation radical oxygenations are considerably enhanced by the presence of weak nucleophiles such as acetate155. The nucleophile is believed to function as shown in Scheme 61. Use of tetraethylammonium acetate in acetonitrile for photooxygenations considerably increases the yield of benzaldehydes and reduces the yield of minor products over a range of substituted stilbenes, as shown in Table 11. 

TABLE 11. Results of photooxygenation of substituted stilbenes (PhCH=CHAr) with 9-cyanoanthracene catalyst in the presence of tetraethylammonium acetate (yields given in percent)"... 

Boyd, J.D. and Foote, C.S. (1979) Chemistry of singlet oxygen. 32. Unusual products from low-temperature photooxygenation of indenes and trans-stilbene. Journal of the American Chemical Society, 101 (22), 6758-6759. 

In fact, the chemiluminescence of an authenic sample of trans- 3,4-diphenyl-1,2-dioxetane, prepared by Kopecky s procedure [118] and then added to the DCA-sensitized reaction on traws-stilbene (E° = 1.51 V vs SCE), totally disappears within a few minutes [119]. In spite of this elegant demonstration, the intermediacy of these short-lived compounds required further direct evidence. In this regard, although different mechanistic pathways can account for the reaction products [34,120,121], Schaap et al. [98] isolated in the DCA-sensitized photooxygenations of adamantylidene-adamantane (E° = 1.46 V vs SCE) 21 and/or of several substituted 2,3-diphenyl-5,6-dihydro-l,4-dioxins (Eox in the range 0.72-1.07 V vs SCE) 22a-f the correspopnding stable 1,2-dioxetanes 23, 24a-f [Eqs. (10,11)] in good yields. 

Oxygenation of C=C and—C=C—. 9,10-Dicyanoanthracene (DCA) sensitizes photooxygenation of some alkenes in CH,CN. The reaction does not involve singlet oxygen and is believed to involve electron transfer. Thus tetra-phenylethylene is oxidized in this way mainly to benzophenone (equation I). Under the same conditions trans-stilbene is oxidized to benzaldehyde. Sulfides are oxidized to sulfoxides and/or sulfones. ... 

Figure 28. Mechanism of benzaldehyde and phenanthrene generation via photooxygenation of cis-and rra .5-stilbene within NaY.

Schaap, A. R, Siddiqui, S., Gagnon, S. D., and Lopez, L., Stereoselective formation of cis-stilbene ozonide from the cosensitized electron-transfer photooxygenation of cis- and trans-2,3-dipheny-loxiranes, /. Am. Chem. Soc., 105, 5149,1983. 

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