Synthesis and Electronic Factors in Thermal Cyclodimerization of Functionalized Aromatic Trifluorovinyl Ethers

A series of 19 p-substituted aromatic trifluorovinyl ether compounds were prepared from versatile
intermediate p-BrC6H4OCFCF2 and underwent thermal radical mediated cyclodimerization to new
difunctional compounds containing the 1,2-disubstituted perfluorocyclobutyl (PFCB) linkage. The synthetic
scope demonstrates the functional group transformation tolerance of the fluorovinyl ether, and the dimers
are useful as monomers for traditional step-growth polymerization methods. 19F NMR spectra confirmed
that p-substitution affects the trifluorovinyl ether group chemical shifts. The first kinetic studies and substituent
effects on thermal cyclodimerization were performed, and the results indicated that electron-withdrawing
groups slow the rate of cyclodimerization. The data were further analyzed using the Hammett equation,
and reaction constants (ρ) of −0.46 at 120 °C and −0.59 at 130 °C were calculated. This study presents
the first liner free energy relationship reported for the cyclodimerization of aromatic trifluorovinyl ethers to
PFCB compounds.