Room Temperature Preparation of Trifluoroethenylzinc Reagent by Metalation of the Readily Available Halocarbon HFC-134a and an Efficient, Economically Viable Synthesis of 1,2,2-Trifluorostyrenes

Abstract

Trifluoroethenylzinc reagent [CF(2)=CFZnX] was generated from the readily available halocarbon HFC-134a by an in situ metalation-transmetalation procedure at temperatures near to room temperature (15-20 degrees C). By systematic standardization of the metalation experiments by manipulation of solvent, cosolvent, temperature, zinc salt, and the base, the trifluoroethenylzinc reagent was produced in 73% yield at 20 degrees C in THF medium. The palladium-catalyzed cross-coupling reaction of the trifluoroethenylzinc reagent with various aryl iodides was carried out under mild reaction conditions to produce 1,2,2-trifluorostyrenes in 59-86% isolated yields. The stability of the intermediate trifluoroethenyllithium reagent was compared at different temperatures and solvent systems. Experimental evidence for the mono-anion from HFC-134a (CF(3)CHF(-)) was obtained by the trapping of the mono-anion with zinc halide in THF/TMEDA medium. The structure and complexation of both the mono- and bis-trifluoroethenylzinc reagents with TMEDA and other ligands are discussed.

One-pot near-ambient temperature syntheses of aryl(difluoroenol) derivatives from trifluoroethanol

“…37, 38 Freshlyprepared LDA (2.5 equivalents) 44 was added to a mixture of 3b and freshly-fused zinc chloride in THF at 0…”

Fluorinated Organozinc Reagents

“…These workers examined the reaction of a wide variety of organolithium bases with the cheap, commercially available CF 3 CFH 2 (HFC-134a) in the presence of anhydrous zinc salts. They established that LDA and anhydrous zinc chloride could effectively react with CF 3 CFH 2 to produce good yields of the trifluorovinylzinc reagent at ambient temperatures 19,20 (15)(16)(17)(18)(19)(20) • C) (equation 33). The in situ production of trifluorovinylzinc from CF 3 CFH 2 was based on previous reports by Coe and coworkers 21 -23 .…”

“…The in situ production of trifluorovinylzinc from CF 3 CFH 2 was based on previous reports by Coe and coworkers 21 -23 . In the presence of the diisopropylamine formed in the metallation reactions, the vinyllithium reagents could effectively compete for the zinc halide to produce the trifluorovinylzinc reagent 20 .…”

Palladium-Catalyzed Cross-Coupling Reactions of Perfluoro Organic Compounds

“…These reactions involve an addition-elimination mechanism, and they often suffer from undesired side-reactions, such as a multi-substitution reaction, even at low reaction temperatures [17,19]. Pd(0)-catalyzed cross-coupling reactions of trifluorovinylzinc, tin, or borate reagents emerged in the 1980s as more direct synthetic methods [24][25][26][27][28][29][30][31][32][33]. A synthetic route involving a more stable trifluorovinyl borate has recently been developed to replace the zinc or tin reagents [34,35].…”