Intramolecular [2 + 2] photocycloaddition/thermal fragmentation: formally "allowed" and "forbidden"pathways toward 5-8-5 ring systems.
The thermal fragmentation of highly functionalized, linear polycyclobutanes with a cis,syn,cis-relative stereochemistry is shown to offer a rapid entry into the dicyclopenta[a,d]cyclooctenyl (5-8-5) ring system. The thermolysis of polyfused cyclobutanes with a cis,syn,cis- or a cis,anti,cis-relationship proceeds in a formally "symmetry-allowed" manner through the intermediacy of a cis,trans-cyclooctadiene. When a bridging tether used to establish the cis,syn,cis-stereochemistry in the intramolecular [2 + 2] photocyclization is present in the thermolysis step, however, the result of a formally "symmetry-forbidden" fragmentation is observed yielding cis,cis-cyclooctadiene-containing 5-8-5 products. In general, the stereochemical observations noted in these fragmentations offer new opportunities for accessing a variety of stereochemical relationships in these 5-8-5 ring systems.
Bader
Scott J
SJ
Department of Chemistry, Merkert Chemistry Center, Boston College, 2609 Beacon Street, Chestnut Hill, Massachusetts 02467, USA.
Snapper
Marc L
ML
D001952:Bridged-Ring Compounds / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003500:Cyclization; D003503:Cyclobutanes / Q000737:chemistry*; D034242:Cyclooctanes / Q000737:chemistry; D006358:Hot Temperature; D015394:Molecular Structure; D010777:Photochemistry
D001952:Bridged-Ring Compounds; D003503:Cyclobutanes; D034242:Cyclooctanes