Fluorovinyl sulfones

The procedure described here provides a stereospecific synthesis of (E)- and (Z)-fluoroalkenes from the corresponding (E)- and (Z)-fluorovinyl sulfones. Fluorovinyl sulfones obtained from ketones are, in most cases, readily separable into (E) and (Z) isomers either by crystallization or by chromatography.4 In the example described, only the (E)-fluorovinyl sulfone 1 is formed (which is converted into the (Z)-fluoroalkene 3 with complete retention of configuration). The reaction sequence has been used for the stereospecific synthesis of fluoroalkene nucleosides5 as well as for... 

Fluoromethylenation.11 Methods for fluoromethylcnation of ketones result in mixtures of (K)- and (Z)-vinyl fluorides, which are difficult to separate. A selective route involves reaction of the ketone with the carbanion of l-fluoro-l-(phenylsulfonyl)methane-phosphonate, prepared from fluoromethyl phenyl sulfones and diethyl chlorophosphate. The reaction provides mixtures of (E)- and (Z)-fluorovinyl sulfones, which can be separated by flash chromatography. Those products cannot be reduced by AI(Hg), but on treatment with tributyltin hydride (A1BN), they are converted into (fluorovinyl)stannancs with retention. Dcstannylation to vinyl fluorides can be effected with sodium methoxide in methanol or with CsF in methanolic ammonia.14... 

LHMDS has also been used for the synthesis of fluorosulfone anion 22 which upon condensation with carbonyl derivatives led to the formation of fluorovinyl sulfone (eq 58). ... 

Much research has been done on the synthesis of perhalogenated P-sultones. The sulfonation of acyclic fluorovinyl ethers leads to a product that is stable up to slightly above room temperature. Thermolysis decomposes the ring structure under SO2 evolution and formation of acid fluorides and perfluorocyclopropane (Eq. 78). )S-Sultones have been synthesized by addition of sulfonyl chlorides to perhalogenated ketones in the presence of triethylamine. The formation of the l-oxa-2-thiacyclobutane 2,2-dioxides appears to require an activated but sterically unhindered carbonyl group because acetone, chloroacetone, trifluoroacetophenone, and p-nitroaceto-phenone did not yield the desired products. ... 

The reaction of fluoromethyl phenyl sulfone with diethyl chlorophosphate at room temperature requires the use of 2 eq of base ( -BuLi, LDA, LiHMDS) to give the lithium salt of diethyl 1-(phenylsulfonyl)-l-fluoromethylphosphonate, which can be hydrolyzed and isolated in 73% yield or reacted in situ with a large variety of carbonyl compounds to form the corresponding a-fluorovinyl phenyl sulfones in moderate to good yields (44-95%, Scheme 3.9). - These sulfones are readily converted into 1-fluoroalkenes via the corresponding (fluorovinyl)stannanes. ... 

V. 1. ition of ketones result in mix-c--> o separate. A selective route I .. ro-l-(phenylsulfonyl)methane-f. r.v-. and diethyl chlorophosphate. j. . inyl sulfones, which can be ir.. o be reduced by Al(Hg), but on r. rted into (fluorovinyl)stannanes K Ltfected with sodium methoxide... 

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