Heterocyclic polyfluoro-compounds. Part 31. Photochemical oxetan formation from fluoroketones and perfluoroaldehydes and 1,2-difluoroethylene

Abstract

The photochemical addition of five fluoroketones (hexafluoro-, chloropentafluoro-, 1,3-dichlorotetrafluoro-, 1,1,3-trichlorotrifluoro-, and 1,1,1-tifluoro-propan-2-one) and the perfluoroaldehydes R_FCHO (R_F= CF₃, C₂F₅, or n-C₃F₇) to (Z)- or (E)-1,2-difluoroethylene at λ > 300 nm has been studied. Oxetan formation dominates with hexafluoropropan-2-one, but there is increasing competition from reactions involving free radicals arising from photolysis of the ketone as the chlorine content is increased. Oxetan formation occurs with little stereospecificity. The aldehydes give r-2-perfluoroalkyl-t-3,c-4-, -c-3,t-4-, and -t-3,t-4-difluoro-oxetans, in the ratio 1.0 :1.7 ± 0.2 :1.3 ± 0.1, respectively, and in high yield (78–94%). A small amount of olefin isomerisation occurred.

Flow pyrolysis of the oxetans from hexafluoroacetone yields (Z)- and (E)-1,2-difluoroethylene and the olefin (CF₃)₂CCHF, the oxetan cis-(CF₂Cl)₂[graphic omitted] yields the olefins (Z)- and (E)-CHFCHF and (CF₂Cl)₂CCHF, and r-2-pentafluoroethyl- or heptafluoro-n-propyl-c-3,t-4-difluoro-oxetans yield mainly the olefins (Z)- and (E)-R_FCHCHF (R_F= C₂F₅ or n-C₃F₇).