A general and efficient route for the preparation of phenyl-substituted vinyl fluorides

alpha-Fluorobenzyl phosphonate (EtO)(2)P(O)CFHPh (2) prepared from diethyl alpha-hydroxyphosphonate (EtO)(2)P(O)CH(OH)Ph (1) and diethylaminosulfur tr ifluoride (DAST),reacts with bases such as butyllithium, tert-butyllithium, lithium bis(trimethylsilyl)amide, or lithium diisopropylamide at -78 degre es in THF to give the phosphonate carbanion [(EtO)(2)P(O)CFPh]-Li+ (3) whic h was detected by acylation with propionyl chloride or by addition of MeOD to the reaction mixture to give (EtO)(2)P(O)CF(COEt)Ph (4) and (EtO)(2)P(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 f luorides 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 .