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

Nucleophilic radicals derived from alkanols and cyclic ethers (cxolane , 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-trichloro-2,3 ,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. T hus the two chlorine atoms in 3 completely reversed the regioselectivi ty to an anti-Kharasch mode. The relative reaction rates were dramatic ally decreased with increasing number of terminal chlorine atoms in ol efins 1-3. The allylic chlorine atom in 1 appeared to mimic a longer p erfluoroalkyl chain. Experimental results were compared with the shape s 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. (C) 1997 Elsevier Science S.A.