Radical addition reactions of fluorinated species Part 6. Regioselectivity of the addition of nucleophilic radicals to halogenopropenes and evidence for a steric effect of the chlorine substituent

Abstract

Nucleophilic radicals derived from alkanols and cyclic ethers (oxolane, 1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane) were employed to test the regioselectivity of addition to 3-chloro-1,1,2,3,3-pentafluoropropene ( 1), 1,3-dichloro-1,2,3,3-tetrafluoropropene ( 2), 1,1,3-trichloro2,3,3-trifluoropropene ( 3) and 1,3-dichloro-2,3,3-trifluoropropene ( 4). The regioselectivity was strongly dependent on the number of chlorine atoms at the terminal position and on the character of the additive, Thus the two chlorine atoms in 3 completely reversed the regioselectivity to an anti-Kharasch mode. The relative reaction rates were dramatically decreased with increasing number of terminal chlorine atoms in olefins 1–3. The allylic chlorine atom in 1 appeared to mimic a longer perfluoroalkyl chain. Experimental results were compared with the shapes of frontier orbitals and electron densities calculated using PM3 and ab initio (3–12G and 6–311 + G **) methods. The transformations of the adducts to chlorofluoroalkyl methacrylates and fluorinated pentane-1,2-diol are reported.