Photooxygenation trisubstituted regioselectivity

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... 

TABLE 19. Regioselectivity in the intrazeoUte photooxygenation of deuterium labelled trisubstituted alkenes ... 

Due to the confined environment and cation-jr interactions within the zeolite cavities as well, it is expected that the regioselectivity in the photooxygenation of trisubstituted... 

Both steric and electronic effects can influence the regioselectivity of ene reactions. For example, a strong preference for hydrogen abstraction from the more substituted side of the double bond of the perepoxide intermediates, generated from trisubstituted alkenes, is observed. This effect has been called the cis effect and explained on the basis of orbital interactions1423 and activation entropy differences.1457 Scheme 6.267 shows the product distribution after photooxygenation of three alkenes (561 563).1461 There is an apparent steric effect of the methyl versus 2-propyl substituents in the first two cases. The cyclopropyl moiety in the last example remains unreacted, which rules out the formation of a biradical intermediate (see also Special Topic 6.10). 

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