Polyhalogenoallenes. Part X. An improved preparation of perfluoro-(3-methylbuta-1,2-diene) and the structure of its dimers

Abstract

Perfluoro-(3-methylbuta-1,2-diene), conveniently prepared by dehalogenofluorination with copper powder of perfluoro-(2-iodo- or 2-bromo-3-methylbut-2-ene), dimerises thermally to give mainly perfluoro-(3-isopropyl-idene-1,1-dimethyl-2-methylenecyclobutane). The reaction of perfluoro-(2-iodo-3-methylbut-2-ene) at higher pressures with copper powder gives a second dimer, perfluoro-(1-isopropylidene-2,2-dimethyl-3-methylene-cyclobutane), together with variable amounts of perfluoro-(2,3,4,5-tetramethylhexa-2,4-diene). The conversion of the first dimer into the second by fluoride-initiated anionic rearrangement is described.