Abstract Two new olefins, CH 2 BrCHBrCH 2 CF CF 2 and CH 2 ClCHClCH 2 CF CF 2, have been prepared as precursors to fluoro β-sultones. The new fluorinated sultone, CH 2 ClCHClCH 2 CFCF2OSO 2, was obtained (from the sulfonation of CH 2 ClCHClCH 2 CF CF 2), along with its rearranged isomer, CH 2 ClCHClCH 2 CF (SO 2 F) C (O) F, and hydrolysis product, CH 2 ClCHClCH 2 CF (SO 2 F) C (O) OH.