1,1,3,3-Tetraoxopolyfluoro-1,3-dithiacycloalkanes CH2SO2(CF2)(n)SO2 (n = 2-5) are synthesized by the reaction of alpha,omega-bis(fluorosulfonyl)perfluoroalkanes FO2S(CF2)(n)SO2F with methylmagnesium chloride or bromide, Depending on reaction conditions, alpha,omega-bis(methylsulfonyl)perfluoroalkanes CH3SO2(CF2)(n)SO2CH3 and probable oligomeric products [CH2SO2(CF2)(n)SO2], are also observed, 2-Substituted products RCHSO(2)(CF2)(n)SO2 (R = CH3, C6H5) are obtained using RCH(2)MgCl. The structures of the phenyl derivatives 5a (n = 2) and 5b (n = 3) were obtained by single-crystal X-ray diffraction analysis.