A kinetic separation method for the stereoselective preparation of 1-fluorovinylphosphonates from E/Z mixtures of 1-bromo-1-fluoroolefins

Reaction of E/Z mixtures of 1-bromo-1-fluoroolefins with diethylphosphite and catalytic Pd(PPh3)4 in triethylamine at 30–40°C gave predominately the (E)-isomer of the 1-fluorovinylphosphonate (E/Z≥95:5) in good yields. Pure (E)-1-fluorovinylphosphonate could be readily obtained by chromatographic separation of the 95:5 E/Z mixture. Pure (Z)-1-bromo-1-fluoroolefin could be recovered and phosphorylated at 70°C to give pure (Z)-1-fluorovinylphosphonate in 51–60% yield. Thus, E/Z mixtures of 1-bromo-1-fluoroolefins could be kinetically separated into pure (E)- and (Z)-1-fluorovinylphosphonates. This methodology provides an unequivocal route to the isomerically pure (E)- and (Z)-1-fluorovinylphosphonates from the readily available 1-bromo-1-fluoroolefins.