The Activation of Carbon−Chlorine Bonds in Per- and Polyfluoroalkyl Chlorides:  DMSO-Induced Hydroperfluoroalkylation of Alkenes and Alkynes with Sodium Dithionite

In DMSO, the addition reactions of perfluoroalkyl chlorides, R(F)Cl, to alkenes or alkynes can occur smoothly in the presence of 1.5 equiv of Na(2)S(2)O(4) and NaHCO(3) at 75-80 degrees C for 4-10 h to give the corresponding adducts (RCH(2)CH(2)R(F) or RCH=CHR(F)). Ethyl chlorofluoro- (1f), chlorodifluoro- (1g) acetates, even nonfluorinated compounds, such as ethyl dichloro- (1h), chloro- (1i) acetates, and chloroform (1j) can undergo the similar reaction. Treatment of omega-iodo (or chloro-) perfluoroalkyl chlorides [X(CF(2))(n)()Cl, n = 2, 4, X= I or Cl] with >3 equiv of alkenes and Na(2)S(2)O(4) gives directly the symmetrically disubstituted alkanes (RCH(2)CH(2))(2)(CF(2))(n)(). The symmetrically and unsymmetrically disubstituted adducts RCH(2)CH(2)(CF(2))(n)()CH(2)CH(2)R' from omega- iodoperfluoroalkyl chlorides can be also obtained stepwise, i.e., through the further addition reactions of monoadducts, RCH(2)CH(2)(CF(2))(n)()Cl to olefins. However, for alpha,omega-dichloroperfluoroalkanes, the similarly stepwise reactions with an alkene is not clean, both bis-adducts and the corresponding omega-hydrides, RCH(2)CH(2)(CF(2))(n)()H as byproducts are also formed. In the absence of alkenes or alkynes, per- and polyfluoroalkyl chlorides can be converted to their sulfinate salts and sulfonyl chlorides.