A novel double olefination. Highly stereoselective synthesis of trifluoromethylated 1,3-butadienylphosphonates

The bisphosphoryl-stabilized carbanion (2), generated from tetraethyl ethyl -l,l-bisphosphonate (1) and n-butyllithium in tetrahydrofuran (THF), was ac ylated by the addition of trifluoroacetic anhydride to give trifluoroacylat ed bisphosphonate (3). Without isolation, 3 was reacted with [(diethylphosp hinoyl)methyl]lithium, and elimination of phosphonic acid anion afforded 4. Treatment of 4 with LDA gave phosphoryl-stabilized carbanion 5, which in t he reaction medium was able to react with aldehyde to give substituted trif luromethylated 1,3-butadienylphosphonates in 66-88% yields with the 1E,3E i somer exclusively or predominately. Thus, the double-olefination methodolog y provides a simple and convenient synthesis of the title compounds. The fi rst example of crystallization of diethyl 1-methyl-2-trifluoromethyl-4-(4'- nitrophenyl)-1,3-butadienyl phosphonate with 1,4-dinitrobenzene was obtaine d by a cocrystallization method. Hence, the configuration of the products c ould be ascertained on the basis of the crystal structure. A possible mecha nism for the explanation of stereochemical results is proposed.