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 a nd catalytic Pd(PPh3)(4) in triethylamine at 30-40 degreesC gave predominat ely the (E)-isomer of the 1-fluorovinylphosphonate (E/Z greater than or equ al to 95:5) in good yields. Pure (E)-1-fluorovinylphosphonate could be read ily obtained by chromatographic separation of the 95:5 E/Z mixture. Pure (Z )-1-bromo-1-fluoroolefin could be recovered and phosphorylated at 70 degree sC to give pure (Z)-1-fluorovinylphosphonate in 51-60% yield. Thus, E/Z mix tures of 1-bromo-1-fluoroolefins could be kinetically separated into pure ( E)- and (Z)-i-fluorovinylphosphonates. This methodology provides an unequiv ocal route to the isomerically pure (E)- and (Z)-1-fluorovinylphosphonates from the readily available 1-bromo-1-fluoroolefins. (C) 2001 Elsevier Scien ce B.V. All rights reserved.