Vinylic sulfides thioethers

Thiols add to alkenes under photochemical conditions to form thioethers, and the reaction can be done intramolecularly to give cyclic thioethers. Thiols also add to alkynes and with a palladium catalyst, vinyl sulfides can be formed. " Selenium compounds (RSeH) add in a similar manner. ... 

Thioethers (sulfides) can be prepared by treatment of alkyl halides with salts of thiols (thiolate ions).7S2 R may be alkyl or aryl. As in 0-35, RX cannot be a tertiary halide, and sulfuric and sulfonic esters can be used instead of halides. As in the Williamson reaction (0-12), yields are improved by phase-transfer catalysis.753 Instead of RS ions, thiols themselves can be used, if the reaction is run in benzene in the presence of DBU (p. 1023).754 Neopentyl bromide was converted to Me3CCH2SPh in good yield by treatment with PhS in liquid NH3 at -33°C under the influence of light.755 This probably takes place by an SrnI mechanism (see p. 648). Vinylic sulfides can be prepared by treating vinylic bromides with PhS in the presence of a nickel complex,756 and with R3SnPh in the presence of Pd(PPh3)4.757 R can be tertiary if an alcohol is the substrate, e.g,758... 

Z-a-Silyl vinyl sulfides are intriguing species since the silyl and the thioether functions exert an opposing polarization on the olefinic bond (Scheme 38). 

The anodic oxidation of a number of vinyl sulfides to produce fluorinated compounds was examined in MeCN-Et3N 3HF on Pt electrodes under controlled-potential conditions [130]. It became evident that the reactivity of the vinyl thioethers depends on, among others, their structure and the nucleophilicity of the medium. Two compounds, PhSCH = CH2 and PhSCH=CHPh, were studied in more detail to evaluate the influence of the different factors upon their electrochemical behavior, and comparisons with that in MeOH Et N 3HF and HOAc-KOAc, leading, respectively, to methoxylation and acet-oxylation were made (Table 3). 

Two reactions of thioethers with phenanthrenequinone have been investigated. As mentioned earlier (cf. Table 3), ethyl vinyl sulfide... 

Metallation of the most simple vinyl ether H2C=CHOCH3 in the a-position has been carried out with Fbutyllithium in THF at low temperatures [81]. Ethene is deprotonated not at all by FBuLi or other strongly basic systems under the same conditions. Sec-butyllithium has been used to metallate alkyl vinyl sulfides H2C=CH—SR [82]. We found that both vinyl ethers and vinyl thioethers can be metallated with excellent results using the cheaper combination of rc-BuLi and fBuOK [9]. The cyclic vinyl ethers 2,3-dihydrofuran and 2,3-dihydropyran can be successfully metallated under the same conditions ... 

The 1-proton in 1,3-dienyl ethers and -thioethers is expected to be more acidic than that in vinyl ethers and vinyl sulfides, because the outer double bond is likely to exert some electron-withdrawing influence. However, addition of the base (in a conjugate fashion) will also be more facile than with the simple vinyl ethers and -thioethers. Reaction of 1-methylthio-l,3-butadiene with butyllithium or butyl-lithium. TMEDA in THF has been shown to result in conjugate addition [91]. The... 

The preparation of vinyl sulfides (or thioethers) has been extended by X-ray or irradiated addition of thiols to acetylene, and Pd(0Ac)2 or Pd(PPh3)4 catalyzed addition of thiol or disulfide to alkynes. In addition, alkyl halides (e.g., ethyl bromide, n-butyl bromide, 5 c-butyl bromide, benzyl chloride, etc.) have been successfully converted into corresponding vinyl sulfide through a one-pot process addition of acetylene mediated by thiourea. 

Vinyl sulfides were hydroformylated with a Rh[(S,S)-BINAPHOS] catalyst to give M-formyl thioethers with excellent regioselectivities and up to 89% ee (Scheme 4.69) [42]. Fastest reaction was noted with aryl vinyl sulfides. 

Examples of the behavior of other substituted vinyl substrates upon exposure to the action of trifluoroacetic acid and triethylsilane are known. For example, -butyl vinyl ether, when reacted at 50° for 10 hours, gives -butyl ethyl ether in 80% yield (Eq. 65).234 In contrast, -butyl vinyl thioether gives only a 5% yield of n-butyl ethyl sulfide product after 2 hours and 15% after 20 horns of reaction.234 It is suggested that this low reactvity is the result of the formation of a very stable sulfur-bridged carbocation intermediate that resists attack by the organosilicon hydride (Eq. 66). 

Bromination of the enol ether product with two equivalents of bromine followed by dehydrobromination afforded the Z-bromoenol ether (Eq. 79) which could be converted to the zinc reagent and cross-coupled with aryl halides [242]. Dehydrobromination in the presence of thiophenol followed by bromination/dehydrobromination affords an enol thioether [243]. Oxidation to the sulfone, followed by exposure to triethylamine in ether, resulted in dehydrobromination to the unstable alkynyl sulfone which could be trapped with dienes in situ. Alternatively, dehydrobromination of the sulfide in the presence of allylic alcohols results in the formation of allyl vinyl ethers which undergo Claisen rearrangements [244]. Further oxidation followed by sulfoxide elimination results in highly unsaturated trifluoromethyl ketonic products (Eq. 80). 

The potassio intermediates give excellent results in a number of derivatizations. For other functionalizations, particularly those with carbonyl compounds, potassium has to be replaced by lithium, this can be done most simply by addition of an equivalent amount of anhydrous lithium bromide, dissolved in THF. Although both vinyl ethers and the corresponding sulfides can be metallated in a short time, it is quite clear from the preparative experiments that the sulfides react faster [9]. A similar difference between oxygen and sulfur compounds has been observed in retaliations of other types of substrates. Some authors have invoked d-orbital effects to explain the easier retaliations of sulfur compounds [83], but an explanation on the basis of polarizability seems more satisfactory [84]. Using the kinetically very active bases mentioned, clean a-metallations of simple vinylic ethers and -thioethers can be realized at low temperatures. Under modified conditions two other processes have been observed [9,85] ... 

Thioethers (sulfides)319 can be converted to their a-carbanion derivative (296, M = Li, Na, K) by treatment with strong bases such as -butyllithium, sodium amide (NaNH2) or potassium amide (KNH2). The hydrogen atom a-to the sulfur atom of sulfides is a weaker acid than that a-to a carbonyl, nitrile or nitro group and stronger bases are required for deprotonation. Sulfides are stronger acids, than the allylic, vinyl, and aromatic hydrocarbons discussed above, however. The various oxides of sulfur can also be converted to a-carbanions. The most important derivatives are the a-carbanions derived from sulfoxides (297). sulfones (298), and... 

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