Photooxygenation alkenes

The argument of the directing effect of lone pairs on the substiment [92] easily extends to the alkyl cases. The orbital interaction (Scheme 20) [103] in the pere-poxide quasi-intermediate suggests the stabilization occurs by the simultaneous interaction of O with two allylic hydrogens on the same side of the alkene. Photooxygenation of trisubstituted olefins revealed a strong preference for H-abstraction from disubstituted side of the double bond [104, 105],... 

Cumyl propyl peroxide, determination, 708 Curing processes, 692, 707 Curtin-Hammett principle, electron-poor alkene photooxygenation, 877 Cyanine dye, TBARS assay, 667 Cyanohydrins, bis(trimethylsilyl) peroxide reactions, 797... 

TABLE 10. Yields of solvent-free alkene photooxygenation on silica or alumina ... 

In a different type of reaction, alkenes are photooxygenated (with singlet O2, see 14-8) in the presence of a Ti, V, or Mo complex to give epoxy alcohols formally derived from allylic hydroxylation followed by epoxidation, for example, ... 

The majority of intrazeolite photooxygenations have been conducted in NaY,84 85 however, one study in the pentasil zeolite ZSM-5 demonstrates that steric confinement effects can play important roles.84 A comparison of the reactions of a series of tri-substituted alkenes in isooctane, NaY, and in ZSM-5 is given in Fig. 21. The reactions... 

Fig. 32 Examples of Wagnerova Type II photooxygenations of alkene, arene, and alkane substrates.

Fig. 35 Mechanism of formation of hydrogen peroxide in the Wagnerova Type II photooxygenation of alcohols and its in-situ use to epoxidize alkenes and oxidized sulfides.

Stratakis, M. (2003). Selective photooxygenation of alkenes by zeolite confinement. In 13th European Symposium on Organic Chemistry, Medimond, V. (ed.), pp. 15-20. Medimond Publishing Co., Bologna... 

Stratakis, M., Nencka, R., Rabalakos, C., Adam, W. and Krebs, O. (2002). Thionin-sensitized intrazeolite photooxygenation of trisubstituted alkenes substituent effects on the regioselectivity as probed through isotopic labeling. J. Org. Chem. 67, 8758-8763... 

Blatter, F., Moreau, F. and Frei, H. (1994). Diffuse reflectance spectroscopy of visible alkene-02 charge transfer absorptions in zeolite Y and determination of photooxygenation quantum efficiencies. J. Phys. Chem, 98(50), 13403-13407... 

Kojima, M., Nakajoh, M., Matsubara, C. and Hashimoto, S. (2002). Photooxygenation of aromatic alkenes in zeolite nanocavities. J. Chem, Soc. Perkin Trans. 2, 1894-1901... 

Wagnerova Class I intrazeolite photooxygenation, 233-253 of alkanes, 234—235 of alkenes, 235-243 regiochemistry, 236, 237, 243, 244 steric confinement effects, 237/ 246-247 Wagnerova Class II intrazeolite photooxygenation, 253-261 of alkanes, 256/ 258-259 of alkenes, 253-257, 253/ 256/ charge-transfer (CT) complexes in, 253-254, 255, 257... 

Figure 9 Products from photooxygenation of trisubstituted alkenes.

In a search for more effective approaches to the problem of stereoselective dioxygenation, alternative methods have been developed. While the inclusion of alkenes and O2 within a chiral cyclodextrin cavity furnished hydroperoxides with modest ee values, neighboring stereocenters and chiral auxiliaries could induce highly stereoselective dioxygenation. In 1987 Kropf and Reichwaldt, and three years later Adam and coworkers reported on the photooxygenation of phenyl-substituted alkenes 36 producing allyUc hydroperoxides 37 and 38 with high diastereoselectivity (dr 80/20). In the best example... 

A great deal of work has been focused on whether the ene reaction proceeds through a concerted or a stepwise mechanism. The initially proposed synchronous pathway was challenged by a biradical , zwitterionic or a perepoxide intermediate. Kinetic isotope effects in the photooxygenation of tetrasubstituted, trisubstituted and cis-disubstituted alkenes supported the irreversible formation of an intermediate perepoxide,... 

TABLE 1. Site selectivity of the photooxygenation of trisubstituted alkenes (cis effect) ... 

Photooxygenation of trisubstituted acyclic 11-13 and cyclic 14 and 15 alkenes illustrates impressively a strong preference for hydrogen abstraction on the less substituted side of the double bond. 

SCHEME 10. Intermolecular isotope effects in the photooxygenation of alkenes 20 vs 22... 

This remarkable and synthetically useful selectivity apphes to both cis and trans non-symmetrically substituted alkenes. The regioselective photooxygenation reaction of some cis non-symmetrical alkenes and their regio-hmitations are shown in Table 5. 

Trans alkenes show similar regioselectivity on their photooxygenation reactions. However, their reactivity towards singlet oxygen is much less than that of the corresponding cis aUtenes. ... 

TABLE 7. Geminal selectivity in the photooxygenation of alkenes 45-48 bearing an aUyUc functionality ... 

SCHEME 16. Mechanism of the geminal selectivity in the photooxygenation of alkenes bearing a large alkyl substituent in allylic position... 

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