Thermal Isomerizations of Fluorinated Spiropentanes

The syntheses and thermal rearrangements and/or fragmentations of 1,1‐difluorospiropentane, 6 , 1,1,4,4‐ and 1,1,2,2‐tetrafluorospiropentanes, 7 and 8 , 1,1,2,2,4,4‐hexafluorospiropentane, 9 , and perfluorospiropentane, 10 , are described., Spiropentanes 6 and 7 undergo only rearrangement to 2,2‐difluoromethylene‐cyclobutane and 1‐(difluoromethylene)cyclobutane and to 2,2,4,4‐tetrafluoromethylenecyclobutane, respectively. Spiropentanes 8 and 9 rearrange and extrude CF 2 : competitively, while perfluorospiropentane extrudes CF 2 : exclusively. Activation parameters are presented for all processes and the mechanisms of these thermal processes are discussed in detail.