STATE-DEPENDENT PHOTOCHEMISTRY OF HIGHLY FLUORINATED BICYCLOOCTA-2,4-DIENES

Article abstract of DOI:10.1016/S0022-1139(00)80220-1

A series of 1,2,3,4,5,6-hexafluorobicyclo<4.2.0>octa-2,4-dienes was subjected to direct irradiation with ultraviolet light and to triplet sensitization.While all of the dienes cyclized smoothly upon direct irradiation to tricyclo<4.2.0.0^2,5>oct-3-enes, their behavior when triplet sensitized was strongly dependent upon the substituents in the 7- and 8-positions.Responses included no reaction, cyclization to tricyclooctene, and fragmentation to hexafluorobenzene plus olefin.Fragmentation occurred only when geminal chlorines were present at the 7-position.This observation is consistent with the view that the four-membered ring opens homolytically at the C6-C7 bond, and only if sufficient stabilization is available for a radical center at the 7-position.