A novel sequential transformations of phosphonate. Highly stereoselective synthesis of perfluoroalkylated alpha-fluoro-alpha,beta unsaturated esters

The phosphoryl-stabilized carbanion 2, generated from diethyl (1-fluoro-1-carbethoxymethyl) phosphonate (1) and n-butyllithium in tetrahydrofuran (THF), was acylated by the addition of perfluoroalkanoic anhydride to give perfluoroacylated phosphonates (3). The latter were reacted in-situ with suitable organolithium derivatives. Elimination of phosphonic acid anion afforded perfluoroalkylated alpha-fluoro-alpha,beta-unsaturated esters in 58-87% yields with the E-isomer produced exclusively or predominately. Thus the sequential transformations of phosphonate provides a convenient synthesis of the title compounds. The effect of base and solvent as well as reaction temperature has been investigated in more detail. A possible mechanism for the explanation of stereochemical results is proposed.