A General and Efficient Route for the Preparation of Phenyl-Substituted Vinyl Fluorides

α-Fluorobenzyl phosphonate (EtO)₂P(O)CFHPh ( 2 ) prepared from diethyl α-hydroxyphosphonate (EtO)₂P(O)CH(OH)Ph ( 1 ) and diethylaminosulfur trifluoride (DAST), reacts with bases such as butyllithium, tert-butyllithium, lithium bis(trimethylsilyl)amide, or lithium diisopropylamide at −78° in THF to give the phosphonate carbanion [(EtO)₂P(O)CFPh]⁻Li⁺ ( 3 ) which was detected by acylation with propionyl chloride or by addition of MeOD to the reaction mixture to give (EtO)₂P(O)CF(COEt)Ph ( 4 ) and (EtO)₂P(O)CFDPh ( 5 ), respectively. Addition of aldehydes or ketones to a THF solution of carbanion 3 led to moderate-to-good yields of phenyl-substituted vinyl fluorides RR′C=CFPh 6 . The stereoselectivity of the products PhCH=CFPh ( 6a ) and Ph(Me)C=CFPh ( 6i ) formed in the reaction was examined. The presence of hexamethylphosphoric triamide or N,N′-dimethylpropyleneurea as cosolvent in the preparation of 6a and 6i increased the (Z)-stereoselectivity. However, the presence of LiCl in THF did not alter the (E)/(Z)-ratio of the product.