摘要：

Acetone-sensitized irradiation of homobenzobarrelenes, exo- and endo- 4a causes the di-π-methane rearrangement (Φ = 3.9 × 10 1 and 9.5 × 10 2 respectively), whereas direct irradiation was ineffective. The products formed were exo- and endo-homobenzosemibullvalenes. On the other hand, irradiation of the dicarbomethoxy derivatives exo- and endo- 4b leads (directly or acetone-sensitized) to dimethyl 7,8- benzotricyclo [4.3.0.0. 2,9] nona-4,7-diene-2,4-dicarboxylate 12 by cyclopropylcarbinyl-homoallyl isomerization (exo- 4b: Φ dir. = 1.8 × 10 2, Φ sens. = 6.9 × 10 2). Herkstroeter- Hammond plots make probable that the same triplet state is photoreactive in all cases.

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