J. Leitich, I. Heise, J. Rust
Jul 1, 2001
Citations
0
Influential Citations
13
Citations
Journal
European Journal of Organic Chemistry
Abstract
The photochemistry (> 300 nm) of 1-cyclohexenyl(phenyl)methanone (1) in the presence of various monoolefins and cyclopentadiene (9) has been investigated. While (Z)-cyclooctene and 1-pentene were unreactive, styrene, (E)-cyclooctene, and diene 9 co-reacted upon irradiation of 1. The reactions observed include [4 + 2] and [2 + 2] cycloadditions of the monoolefins to the primary photoproduct of 1 (which is the trans isomer 2), and trapping reactions of the 2-oxyallyl compound 4 formed thermally from 2 as a secondary intermediate. The trapping reactions of 4 are ene-type additions of the olefins, analogous to those observed with the prototypical 2-oxyallyl compound 18 in purely thermal reactions, and involving a hydrogen transfer from 4 to olefin to give adducts 10, 12, 13, 24, and 25. However, while 18 gives one single ene-type adduct with 9, intermediate 4 displays two regioisomeric ene-type addition modes with 9, both of which are concerted, albeit nonsynchronous. In the mode resulting in 10, it is suggested that hydrogen transfer lags behind C−C bond formation, whereas the reverse holds for the mode affording 12 and 13. For both major adducts, 10 and 12, concerted formation requires endo orientations of the two π systems.