Reaction of Halothane with sec-butyllithium in the presence of zinc halides—one-pot preparation of chlorodifluorovinylzinc reagent and its derivatization to α-chloro-β,β-difluorostyrene

Room temperature preparation of α-chloro-β,β-difluoroethenylzinc reagent (CF2CClZnCl) by the metallation of HCFC-133a (CF3CH2Cl) and a high yield one-pot synthesis of α-chloro-β,β-difluorostyrenes

“…of LDA was used as a base at À78 8C in this metallation reaction. Our observations differ with the results reported by Kumudaki during the metallation of Halothane TM in the presence of zinc chloride [20][21][22]. We have not observed any species corresponding to his reported new zinc reagent and the small amount of zinc reagent formed was spectroscopically similar to the chlorodifluorovinylzinc reagent generated by the metallation of CF 3 CH 2 Cl [23].…”

“…We have not observed any species corresponding to his reported new zinc reagent and the small amount of zinc reagent formed was spectroscopically similar to the chlorodifluorovinylzinc reagent generated by the metallation of CF 3 CH 2 Cl [23]. The yield of the zinc reagent formed during the metallation of Halothane TM was not mentioned in his report [22]. It is also not clear why a large excess of zinc reagent (4 equiv.)…”

“…Kumudaki and co-workers reported the generation of the a-chloro-b,b-difluorovinylzinc reagent under relatively higher temperature (À60 8C) by the metallation of CF 2 CHCl [20,21] and 1-bromo-1-chloro-2,2,2-trifluoroethane (Halothane TM ) [22]. But the interpretation of this zinc reagent as a new zinc reagent compared to the zinc reagent generated by the Normant procedure was questionable, and the spectral data described were different from each other.…”

Fluorinated Organozinc Reagents

“…Also, this work (at −60 • C) did not solve the problem of low-temperature reactions. Kumadaki and coworkers recently reported the use of CF 3 CHClBr (Halothane) as a precursor to [F 2 C=CClZnCl] (equation 31); however, the yield of the zinc reagent was not reported 17 . Although Kumadaki reports reasonable yields of coupled products employing Halothane as a precursor, this precursor in our hands did not cleanly give high yields of the zinc reagent (equation 32) 18 .…”

“…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 .…”