An Extraordinarily Rapid Polymerization of Vinylpentafluorocyclopropane:  Highly Stereo- and Regioselective Synthesis of Unsaturated Fluoropolymers<sup>†</sup>

2003-01-01T00:00:00Z (GMT) by Zhen-Yu Yang
Vinylpentafluorocyclopropane <b>1</b> was prepared from the reaction of 1,1,2-trifluoro-4-bromobutene and hexafluoropropylene oxide at 190 °C, following by treatment with KOH. <b>1</b> is stable at low temperature (−40 °C) for 7 years, but it rearranged readily to 2,3,3,4,4-pentafluorocyclopentene-1, <b>2</b>, at above 80 °C (<i>E</i><sub>a</sub> = 28.7 kcal/mol). Under radical conditions, <b>1</b> extraordinarily rapidly polymerizes to give highly crystalline <i>Z</i>-fluoropolyolefin (CF<sub>2</sub>CF<sub>2</sub>CFCHCH<sub>2</sub>)<i><sub>n</sub></i>, <b>3</b>, which is very useful for cross-linking and grafting but difficult to obtain by other means. The stereochemistry of <b>3</b> was further confirmed by radical addition of iodine to <b>1 </b>to form <i>Z</i>-ICF<sub>2</sub>CF<sub>2</sub>CFCHCH<sub>2</sub>I, <b>4</b>, exclusively. The rapid polymerization with high stereoselectivity and regioselectivity could be rationalized by effects of a favorable polar transition state of a high ring strain and electron-deficient pentafluorocyclopropyl and a relative electron-rich double bond of <b>1</b>.