| The thermal fragmentation of highly functionalized, linear tricyclobutanes has proven to be a rapid entry into dicyclopenta[a,d]cyclooctenyl (5-8-5) ring systems. Of particular interest is the manner by which the thermolysis of polyfused cyclobutanes occurs, as well as the stereochemical outcome of the fragmentation. A cis,syn,cis- or a cis,anti,cis-relationship of fused cyclobutanes traditionally proceeds through a formally "symmetry-allowed" manner through the intermediacy of a cis,trans-cyclooctadiene. However, when a bridging tether that restricts conformation freedom is present, the result of the thermal fragmentation is a formally "symmetry-forbidden" fragmentation. The ability to control the outcome of these fragmentations allows its application towards the synthesis of the core structure of kalmanol. |
