Christopher Owen Bender
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Donald Laverne Bengtson
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Douglas Dolman
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Carolyn Elaine L. Herle
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Seamus Francis O'Shea
1,6- and 1,8-Dimethylbenzotricyclo[3.3.0.02,8]octa-3,6-diene (16 and 14) are the major semibullvalene products formed from acetophenone sensitized irradiations of the barrelenes 2,6- and 2,3-dimethyl-1,4-dihydro-1,4-ethenonaphthalene (37 and 22), respectively (Φ37→16 = 0.65; Φ22→14=0.57). The direct (Φ14 = 0.017) or chlorobenzene sensitized (Φ14 = 0.12) irradiation of 14 yields 2,3-benzo-5-methyl-6-methylenebicyclo[3.3.0]octa-2,7-diene (17), a transformation typical of methylcyclopropanes. Gas phase thermolysis (420 °C/6 Torr) of 14 gives 6,7-dimethylbenzocyclooctatetraene (15). The direct irradiation (Φ39 = 0.003) or the gas phase thermolysis (395 °C/6 Torr) of 16 gives 6,9-dimethylbenzocyclooctatetraene (39). The rearrangement 14 → 17 is in accord with predictions based upon CNDO-CI calculations of changes in atom–atom interaction energies on excitation to the S1 or T1 excited states of 14.