Conversion to vinyl sulfides

Thioazolium ions, as catalysts for conjugate addition of aldehydes, 59, 57 Thiobutyric acid, 55, 129, 131 Thioketals, conversion to vinyl sulfides,... 

Trimethylsilyl iodide (TMS-I) can be used as an activating agent in the conversion of sulfoxides to vinyl sulfides providing a sufficiently reactive hindered base, i.e. DIPEA, is employed (Scheme 32). When dibutyl sulfoxide (136) is treated with TMS-I in the presence of HMDS rapid formation of dibutyl sulfide and iodine is observed, indicating that HMDS is too weak a base to effect deprotonation at a rate competitive with iodide ion displacement. Note also that this procedure can be used to prepare 1-thio-phenyl-1,3-butadienes (137) and that either allylic or vinyl sulfoxides can be used as the precursors to these synthetically useful dienes. 

Conversion of vinyl sulfide (74) to the target natural product is outlined in Scheme 4.40. 

Elimination of Thiophenol from Thioacetals. Conversion of thioacetals to vinyl sulfides is accomplished under exceptionally mild conditions by treatment with (CuOTOa-CeHe (eq 45). The reaction involves an a-phenylthio carbocation intermediate. Three factors contribute to the effectiveness of this synthetic method the Lewis acidity of a copperfT) cation that is unencumbered by a strongly coordinated counter anion, the solubility of the copper(I) triflate-benzene complex, and the insolubility of CuSPh in the reaction mixture. An analogous elimination reaction provides an effective route to phenylthio enol ethers from ketones (eq 46). ... 

The nickel-catalysed reaction of aryl, allyl or vinyl sulfides with Grignard reagents has been found to be an effective way for the conversion of carbon-sulfur bonds into carbon-carbon bonds [318]. However, simple aliphatic substrates are inert. 

Lactone ring expansion.1 The 7-lactone 2 can be expanded to the protected y-lactol 4, characteristic of mevinic acids, by reaction of the lactol of 2 with this Wittig reagent to provide a vinyl sulfide 3. Conversion of the vinyl sulfide to 4 was... 

The same reaction can be used for conversion of ketene bis(phenylthio)acetals (3) to the vinyllithium reagents 4. This method may be more useful in some cases than deprotonation of vinyl sulfides. Thus 4 generated in this way reacts as expected with cyclohexanone and carbon dioxide. Both these reactions fail when 4 is generated by deprotonation of vinyl sulfides. 

Vinyl sulfides have been prepared by the catalytic addition of the S—H bond of thiols (85) to terminal alkynes (86) under solvent-free conditions using the nickel complex Ni(acac)2 (47). High alkyne conversions (up to 99%) were achieved after 30 min at 40 °C in favor of the corresponding Markovnikov products (87) (equation 23). Other metal acetylacetonate complexes were examined for this reaction, but none showed any improvement over the nickel catalyst. Mechanistic details suggest that alkyne insertion into the Ni—S bond is important to the catalytic cycle and that nanosized structural units comprised of [Ni(SAr)2] represent the active form of the catalyst. Isothiocyanates and vinyl sulfides have been produced in related Rh(acac)(H2C=CH2)2 (6) and VO(acac)2 (35) catalyzed sulfenylation reactions of aryl cyanides and aryl acetylenes, respectively. 

In the present context, the term electron rich alkenes refers primarily to enol ethers, enol sulfides, and A-vinylamides or A-vinylamines. Such alkenes are typically much more readily ionizable than are simple alkenes. The conversion of these substrates to the corresponding (highly electron deficient) cation radicals represents a sharp Umpolung. The Diels-Alder additions of tra j -anethole, phenyl vinyl ether, phenyl vinyl sulfide, 1,3-dioxole, and A-methylindole to 1,3-cyclohexadiene have been reported (Scheme 22) [49, 52]. 

Reaction of 2-phenylsulfinyl esters such as (133) with acetic anhydride is slow at room temperature, but when a catalytic amount of methanesulfonic acid is present in the reaction medium, conversion to the vinyl sulfide (134) is complete after a few hours at 20-40 C (Scheme 31). Mixtures of ( )/(2) isomers are usually obtained, with the (2)-isomer generally being the more stable. These isomers are in-terconverted on heating, a process which occurs slowly on standing, even in the dark. The discovery that photochemical or free radical induced 1,3-shift of the PhS group in (135) to the y-position can be effected offers an additional opportunity to modulate the a/y selectivity in the extended enolate chemistry of a,3-unsaturated carbonyl systems. 

Conversion off ketones into unsaturated aldehydes.1 The reagent (1) is converted into the anion (2) by sec-butyllithium in THF at —78°. This anion reacts with a ketone to give an allyl vinyl sulfide (3) in yields generally in the range... 

A. Phenyl vinyl sulfide. In a 1-L, three-necked, round-bottomed flask fitted with magnetic stirrer, condenser, addition funnel, and nitrogen inlet tube is placed 400 mL of ethanol. Sodium metal ( 3 g, 1 g-atom), cut into small pieces, is added with stirring. When conversion to sodium ethoxide is... 

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