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 RFCHO (RF= 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)-RFCHCHF (RF= C2F5 or n-C3F7).