Reaktive EC(p–p)π-Systeme, XXXII[1a] Phosphorylide Me3P = C(X)P(F)CF3 mit π-Donor-Substituenten X = F, OMe, OEt

Fluorophosphaalkenes of the type F3CP = C(X)F react with trimethylphosphane in a 1:1 molar ratio at temperatures below -20-degrees-C to give the novel phosphorus ylides Me3P = C(X)P(F)CF3 in good yields [X = F (4), 70%; OMe (7), 62%; OEt (8), 74%]. Compounds 4, 7 and 8 are stable up to about 10-degrees-C, but decompose at higher temperatures yielding in case of 4 Me3PF2 as main product. The P-31-NMR spectra indicate a high barrier of rotation for the F3C(F)P group around the P(III)-sp2C bond. The new ylides owe their existence to the electron withdrawing effect of the F3C(F)P unit which overcompensates the destabilizing influence of the fluorine or alkoxy substituents on the sp2C atom.