Oxetanes strained tricyclic

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. 

Laureacetal-B (70) is a tricyclic oxetane recently isolated from a marine alga. It has the interesting features of bromine substitution and a cyclic acetal structure. In view of the extreme ease of hydrolysis of 2-methoxyoxetane, it seems surprising that a strained ring cyclic acetal would be isolated from a marine source. Its structure assignment is based on spectral studies and chemical transformations (79CL301). 

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