Difluorovinyl lithium

Figure 2.19 Difluorovinyl lithium enolates stabilized by heteroatom. ...

Difluoroethylene (47) is a useful building block for the preparation of 1,1-difluoroolefins. The vinylic fluorine atoms stabilize the difluorovinyl lithium 48 formed by treatment of 47 with sec-BuLi at -115°C. This carbanTon can be quenched with aldehydes (19,29,30) or carbon dioxide (31) to provide 1,1-difluoroolefins (49,50) which are of utility for further transformations (Scheme 137. Similarly, trifluoroethylene (51) has been utilized to prepare 1,2-difluoroolefins, such as 53 (Scheme 16) (32). Difluoroacetylene 52 was implicated as an Intermediate. 

Difluorovinyl-lithium has been generated and allowed to react with COg to provide a new synthesis of a -unsaturated 3-fluoro-acids and their derivatives (Scheme 16). ... 

Hence, new, general syntheses of useful fluorine compounds are desirable, and in this context the difluorovinyl-lithium (55), prepared from 2,2-difluoroethene, appears to have versatility some of its reactions reported this year are shown in Scheme 3. 

Trifluorovinyl lithium (prepared from 1,1,1,2-tetrafluoroethane) was allowed to react with 2-trifluoromethylaniline 29 at -78 °C to give 1,2,3-lrifluoroquinoline 33a in moderate to good yield. In a similar cyclization with aniUne 29 l-chloro-2,2-difluorovinyl lithium (prepared from l-chloro-2,2,2-trifluoroethane) afforded 2-chloro-l,3-difluoroquinoline 32b (Scheme 13) [22]. 

Burdon J, Coe P, Haslock I, Powell R (1997) Reactions of trifluorovinyl lithium and l-chloro-2,2-difluorovinyl lithium the synthesis of fluorinated heterocycles. J Fluorine Chem 85 151-153... 

Nucleophilic addition of alkyl lithium to difluorovinyl-substituted epoxide (48) proceeds on the difluoromethylene carbon via the addition-ring opening pathway [16]. However, trimethylaluminum reagent transfers the methyl group at the carbon remote from the difluorinated carbon of 50 presumably via the Lewis acid catalyzed ring opening-addition mechanism as shown in Scheme 2.26. 

A number of Claisen rearrangements of allyl vinyl ethers have been reported. Thus allyl 2-diloro-l,2-difluorovinyl ether, prepared by the alkoxide-catalysed addition of allyl alcohol to chlorotrifluoroethylene, followed by dehydrofluoiination with n-butyl-lithium at —SO °C, rearranges at-35 C ... 

Substitution on 2,2-difluorovinylic carbon has been examined by using ab initio MO calculations. For a model borate, lithium 2,2-difluoro-l-mesyloxyvinyl(trimethyl) borate (1), three feasible mechanisms were investigated the SNl-like, the Sn2-type, and the addition-elimination mechanisms. Four transition states were obtained. 

To obtain quinolines bearing fluorine atoms in the pyridine ring, cyclizations of fluorinated ortho-vinylphenylnitriles and isonitriles proved to be an effective approach. Indeed, 3-fluoroquinolines 48a-d have been obtained by cyclocondensation of organometallic reagents with 2-(2,2-difluorovinyl)phenyl substituted isonitriles 47 (Scheme 17). 2-(2,2-Difluorovinyl)anilines 45, derived from the reaction of 2,2,2-trifluoroethyl tosylate, butyl magnesium salt of 2-iodoaniline, butyl lithium and triaUcylborane, have been transformed into isonitriles 47 [27, 28]. 

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