Heterocyclic polyfluoro-compounds. Part 33. Competing 1,2- and 1,4-photochemical addition of hexafluorobiacetyl to 1,2-difluoroethylene

Abstract

Photochemical addition of hexafluorobiacetyl (λ > 300 nm) to either cis- or trans-1,2-difluoroethylene yields mainly cis-2,3-difluoro-5,6-bis(trifluoromethyl)-2,3-dihydro-p-dioxin (53–57%), and the corresponding trans-dioxin (12%) by 1,4-addition, together with r-2-trifluoromethyl-2-trifluoroacetyl-t-3,t-4-difluoro-oxetan (7–8%) and the corresponding t-3,c-4-(7–8%) and c-3,t-4-oxetans (6–7%) by 1,2-addition.

The cis-dioxin yields both cis- and trans-1,2-difluoroethylene upon pyrolysis, and with aluminium trichlorode undergoes isomerisation to the trans-dioxin, and non-stereospecific exchange of one or both ring fluorines by chlorine atoms.