Difluorovinyl Compounds

The silylated compound can be reacted further with other organohthium compounds to give substituted silylated difluorovinyl compounds (equation 34)... 

Vinyl fluorides can also be prepared starting from difluorovinyl compounds via the loss of a fluorine atom by an addition-elimination process, as illustrated in Figure 2.9." ... 

The catalytic hydrogenation of difluorovinylic compounds affords C-difluoro-methyl glycosides and 2-, 3-, or 5-C-difluoromethyl sugars vide supra) (Figure 6.29). In the a-pyranose series, hydrogenation of the exocyclic double bond occurs on the jS... 

As previously reported, the radical addition of CF2Br2 on glycals (initiated by sodium dithionite) affords difluorobromomethylated compounds. These latter molecules are easily dehydrohalogenated in the presence of TBAF. Under such conditions, these difluorovinyl compounds can add a fluoride ion (from TBAF). The subsequent elimination of the acetate moiety yields trifluoromethyl unsaturated compounds. The double bond can then be reduced (Figure 6.37). The same kind of reaction occurs in the presence of DAST with gcm-difluor-omethylene compounds, which are obtained by addition of an ylide onto an ulose (Figure 6.37). 

Trifluorovinyllithium on reaction with trimetkylchlorosilane yields a tri-methylsilyltrifluoroethylene, which itself is a new and useful synthon for the preparation of difluorovinylic compounds [66] (equation 33)... 

The scope of this methodology was extended to the enantioselective rearrangement of difluorovinyl allyl ethers by these authors, furnishing a novel powerful tool for the synthesis of chiral p-substituted a,a -difluorocarbonyl compounds. As shown in Scheme 10.36, moderate to good enantioselectivities... 

They could be trapped with a variety of electrophiles such as aldehydes, water, carbon dioxide, trimethylsilyl chloride, tributyltin chloride to give the corresponding difluorovinyl derivatives [132-138] (Scheme 52), which were demonstrated to be versatile and useful building blocks for the synthesis of organo-fluorine compounds. 

Difluorovinyl ahyl ethers can be similarly rearranged. The preparation of 8-subshtuted, a,a-difluorocarbonyl compounds (5) is possible upon treatment of 4 with 1.5 equiv of (5,5)-1 in the presence of 1.5 equiv of EtsN in CH2CI2 at -78 °C, and then stirring at ambient temperature (eq 2). 

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. 

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