Photochemical Reactions. 129th Communication. Photochemistry of a conjugated diepoxydiene: Product formation via carbonyl ylide and carbene intermediates with participation of neighbouring epoxy functions

Abstract

In memoriam Hans Heusser (8.VI. 83) SummaryOn singlet excitation (A = 254 nm, acetonitrile) the diepoxydiene (E)-7 undergoes photocleavage to the carbonyl ylide VII and the carbenes X and XI. The carbonyl ylide VII rearranges to the thermally labile dioxabicyclo [3.2.1 Ioctene 20 or fragments via VIII to the aldehyde 9 and propyne. The carbene X, showing behaviour typical of vinyl carbenes, undergoes addition to the adjacent double bond furnishing the cyclopropene 11. The carbene XI, however, undergoes an insertion reaction into the neighbouring oxirane C, C-bond leading to the oxetene (E)-21 which can be isolated at -78", but at room temperature is rapidly transformed to the aldehyde 10.On triplet excitation (acetone, A > 280 nm), however, (E)-7 shows the typical behaviour of epoxydienes, undergoing C, 0-cleavage of the oxirane and isomerization to 22,23 and (E/Z)-24.

Photochemical reactions. 146th communication. Photochemistry of conjugated methano‐epoxydienes: Participation of the neighboring cyclopropane ring in product formation via carbonyl ylide and carbene intermediates

“…Part). It was observed previously, that 2H-pyrans of type 12 are rather labile [6]. Therefore, 12 was transformed by reaction with '02 to the more stable endoperoxide 19 (Scheme 3) which showed spectral data (see Exper.…”

“…Concluding the discussion, it may be noted that on triplet sensitization (A > 280 nm, acetone), (E)-7 shows behavior typical of epoxydienes [5] [6] undergoing cleavage of the C-0 bond of the oxirane to i and formation of the known types of compounds 13,14 and (E/Z)-15 (Scheme 6 ) . …”

“…a carbene intermediate, which were normally formed on z,n: *-excitation of epoxyenones [3] [4] could not be detected. Since epoxydienes are known to undergo preferentially isomerizations uia carbene intermediates [5] [6], the behavior of the epoxydienes (E)- 6 and (E)-73) (Scheme 2) was investigated. In particular, it was expected that the results of the singlet excitation of (E)- 6 and (E)-7 could give some information on the reactivity of a photochemically generated carbene next to the cyclopropane.…”

“…Therefore, 12 was transformed by reaction with '02 to the more stable endoperoxide 19 (Scheme 3) which showed spectral data (see Exper. Part) analogous to a similar compound [6]. Dihydrofurans 13 and 14, and Cyclohexanones (E/Z)-15.…”

“…Dihydrofurans 13 and 14, and Cyclohexanones (E/Z)-15. Their structure and relative configuration were assigned by comparison of the spectral data with that of previously obtained analogs, either which an oxirane instead of the cyclopropane [6] or without a cyclopropane moiety [5]. Finally, the diastereoisomeric dihydrofurans 13 and 14 were transformed to the lactone 20 (Scheme 3) by oxidation with Ni02 [8].…”