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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 C 6 C 7 bond, and only if sufficient stabilization is available for a radical center at the 7-position.

A method is described for the rapid and stereoselective assembly of E-trisubstituted olefins by a convergent process from three components

Lewis-acid catalyzed reactions of unsaturated epoxides 1 and 2 afford the unprecedented products 3 and 5, respectively. Mechanistic pathways for these reactions are presented (Schemes 2 and 4) along with a more fundamental analysis.