Reduction of Vinyl Sulfones

It is interesting to note that both diastereoisomers of 204 afford solely the ( )-olefin 207 in a convergent process. Of the various possible conformers of cation 206, the one possessing the R and aryl substituents in a trans relationship is clearly the most stable, and the reaction is thus channelled through this intermediate. 

Both ( )- and (Z)-vinyl sulfones can be readily prepared by several methods, and it is therefore little wonder that their transformation to stereodefined alkenes has been investigated. Both isomers of vinyl sulfones can be obtained by elimination from erythro- or threo-JJ-tosyl sulfones [46], generated either by controlled reduction of j8-keto sufones [46, 118] or by varying the base in the coupling step [131]. The reduction of disubstituted vinyl sulfones by Na2S204, discovered by Julia et al. in 1982, is particularly efficient and highly stereoselective [93] (Table 3.9). 

This approach has since been extended by Julia et al. to the synthesis of trisub-stituted olefins by replacing the sulfone moiety with an alkyl group. Some examples are collected in Table 3.10 [58]. 

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Transition-metal-catalyzed stereoselective reductions of vinylic sulfones with Grignard reagents are achieved with excess n-BuMgCl in tetrahydrofuran at room temperature.196,48 Better yields and selectivities are obtained with palladium catalysts [Pd(acac)2] than with nickel complexes such as [Ni(acac)2], especially if external ligands such as DABCO, triethylamine (TEA), or (n-Bu)2P are used.196,48 Nickel catalysts are used more often for reducing sulfonyl-1,3-dienes than palladium catalysts. When using this method, it is very important to remove the catalyst before isolation of the products in order to avoid isomerization of the... 

From a mechanistic viewpoint, the reduction of vinyl sulfones and the reductive elimination of /f-acetoxy sulfones with Na(Hg) or Sml2 are the only procedures to have been investigated to any great extent. Recent work published by Keck et al. [105] has shown that different mechanisms are operative when Na(Hg)/MeOH or Sml2/HMPA are employed. They set out to study the reductive desulfonylation of several vinyl sulfones under two sets of reaction conditions, specifically 8 equiv. Sml2, N,N-dimethylpropyleneurea (DMPU), MeOD, 60 min. and 5% Na(Hg), Na2HP04, THF/MeOD (4 1), 0 °C, 60 min (Table 3.5). 

Hydrogenolysis of vinyl sulfones.2 Vinyl sulfones are reduced by Na2S204 and NaHC03 in aqueous ethanol with retention of configuration. The reaction is facilitated by use of a phase-transfer catalyst such as Adogen. The reduction involves addition of HSOz to form a sulfone sulfinate salt which can be trapped by CH3I. The overall reaction thus involves a (3-syn-addition followed by an anti-elimination. This hydrolysis was used in a synthesis of several insect pheromones, such as (Z)-8-dodecenyl-l-acetate (1). 

Reductive Annulatlon of Vinyl Sulfones. B1cyclo[4. 3. 0]hon-l-en-4-one H. -S. Lin and L. A. Paquette, Department of Chemistry, The Ohio State University, Columbus, OH 43210... 

Reductive desulfurization of 9-(phenylsulfonyl)furo[2,3- ]quinoline and its 2-methyl derivative can be effected by treatment with LAH in THF solution at reflux, but proceeded poorly with aluminum amalgam, the reagent of choice for the reductive cleavage of vinyl sulfones <83JOC774>. Raney nickel was used to remove a thiomethyl substituent from the central ring of a furochromone direct precursor to visnagan <89JOC448l>. 

Lithiation of vinylic sulfones. Phenyl vinyl sulfones (1), prepared as indicated, react with methyllithium regiospecifically at — 95° at the a-vinyl position to give the lithium derivatives 2. As expected, 2 can be alkylated to give 3. The reaction of 2 with enolizable carbonyl compounds proceeds more satisfactorily by prior conversion to the vinylic Grignard reagent a. This sequence constitutes a route to disubstituted alkenes, since a sulfone group is reductively cleaved by sodium amalgam (7, 326). ... 

Julia has undertaken studies on the selective reduction of keto sulfones, followed by the trans elimination to the vinyl sulfone. These intermediates can then be reacted with Grignard reagents to produce trisubstituted alkenes. ... 

REDUCTIVE AHNULATION OF VINYL SULFONES BICYCL0[4.3.0]N0N-l-EN-4-0NE (5H-Inden-5-one, 1,2,3,3a,4,6-hexahydro-)... 

The reductive desulfonylation of vinylic sulfones has been mainly carried out with sodium and aluminum amalgams, Sml2, and Mg in M,Al-dimethyl-formamide (DMF) in the presence of chlorotrimethylsilane (TMSC1). The configuration of the double bond is not necessarily preserved in the desulfonylation of vinylic sulfones when Na/Hg is employed. This reagent is the most widely used when there is no need for stereochemical control as shown in Eqs. 2139 and 22.40... 

Table 7. Reductive Desulfonylation of Vinyl Sulfones (Continued)...

Reduction of Alkynyl Sulfones. The HSiEt2Me/Cu(OTf)2 system reduces alkynyl sulfones to cis vinylic sulfones (eq 13). The yields with copper(II) tetrafluoroborate are higher than those with Cu(OTf)2. Dimeric side products are formed in some cases. 

The organolithium reagent (1) also reacts with a wide variety of other electrophiles, including silyl chlorides to provide bis(silyl)methane derivatives, and nitriles to provide -sUyl amines after in situ reduction of the intermediate imine derivative. a-Silyl epoxides are opened to provide the substituted vinylsilane. Reaction of (1) with arenesulfonyl fluorides provides a-silyl sulfones, key intermediates for the preparation of vinyl sulfones. Reaction of the lithium reagent (1) with alu-... 

The reduction of vinyl halides, R5C=CX — R2C=CH, is included in section 150 (Hydrides from Halides and sulfonates)... 

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