Dihydroazulene synthesis

Scheme lb Synthesis of dihydroazulenes via corresponding vinylheptafulvenes AT = reflux. 

Early reports by Kossanyi and coworkers illustrate the variety of strained products that can be obtained from intramolecular photoreactions. For example, irradiation of 2-allylcyclohexanone gave a mixture of (186 32%), (188 22%) and (189 14%), the latter two arising presumably from decomposition of the strained tricyclic oxetane (187). In a related azulene synthesis,Kossanyi obtained high yields of oxetanes (190) and (191), the latter comprising 80% of the reaction mixture. When thermolyzed, compound (191) formed a mixture of isomeric dihydroazulene compounds that could be dehydrogenated (Pd/AhOs) to form azulenes. 

Cehk, M., Akbulut, N., and Balci, M., Synthesis and chemistry of endoperoxides derived from 3,4-dihydroazulene-l(2H)-one an entry to cyclopentane-anneUated tropone derivatives, Helv. Chim. Acta, 83, 3131, 2000. 

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