Allyl difluorovinyl ethers

Scheme 10.36 Claisen rearrangements of difluorovinyl allyl ethers with sulfurcontaining boron catalyst.

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... 

Tributylsilyl)trifluoroethene has been used as a precursor to the vinylic fragment.1516 This variation of the original methodology10 avoids the need for butyllithium, since proto-desilylation to give allyl difluorovinyl ether intermediates 34 is achieved with tetrabutylam-monium fluoride. The 2-fluoroalk-4-enoie acid derivatives 35 are produced in a one-pot procedure (Table 11). Various mechanistic possibilities have been discussed in order to account for the stereochemical outcome.16 The need for two equivalents of allylic alcohol limits the utility of this method. 

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 ... 

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