Vinyl sulfides, formation

Problems can arise at the last stage due to difficulties in die isolation of die aldehyde and/or preferential vinyl sulfide formation. Nonetheless, the method has some potential Sulfoxides are prone to thermal elimination, and this has been used by Trost in his mediod, which can also be used for the oxidation of primary amines (Scheme 14). The procedure is limited to benzylic and allylic bromides. 

Vinyl sulfides are prepared from sulfoxides under a variety of conditions. These include reaction with acetic anhydride at reflux, with trifluoroacetic anhydride in the presence of an amine base and with acetic anhydride in the presence of an acid catalyst. In fact, precautions must be taken in certain Pum-merer reactions discussed in the preceding sections to avoid competing vinyl sulfide formation. 

Many carbon nucleophiles tend to he too basic for successful addition to the carbocationic center provided by DMTSF activation of dithioacetals and usually result in vinyl sulfide formation. In addition, the Mc2S generated competes for the electrophilic center. Allylstannanes overcome these constraints and successfully generate new carbon-carbon bonds (eq 12). DMTSF activation of a thioacetal resulted in an electrophilic cyclization at the 3-position of a 3-substituted indole. ... 

Formation of Sulfides. Thiols react readily with alkenes under the same types of conditions used to manufacture thiols. In this way, dialkyl sulfides and mixed alkyl sulfides can be produced. Sulfides are a principal by-product of thiol production. Mixed sulfides can be formed by the reaction of the thiol using a suitable starting material, as shown in equations 21, 22, and 23. Vinyl sulfides can be produced by the reaction of alkynes with thiols (38). 

Vinyllithium [917-57-7] can be formed direcdy from vinyl chloride by means of a lithium [7439-93-2] dispersion containing 2 wt % sodium [7440-23-5] at 0—10°C. This compound is a reactive intermediate for the formation of vinyl alcohols from aldehydes, vinyl ketones from organic acids, vinyl sulfides from disulfides, and monosubstituted alkenes from organic halides. It can also be converted to vinylcopper [37616-22-1] or divinylcopper lithium [22903-99-7], which can then be used to introduce a vinyl group stereoselectively into a variety of a, P-unsaturated systems (26), or simply add a vinyl group to other a, P-unsaturated compounds to give y, 5-unsaturated compounds. Vinyllithium reagents can also be converted to secondary alcohols with trialkylb o r ane s. 

Cycloadditioiis in which 1,2-dithietes acted formally as dienes are among the most typieal reaetions of 1,2-dithietes. Tire dithiete 144 is highly reaetive and eapable of reaetions even with simple alkenes and alkynes (60JA1515 61JA3434,61JA3438).Tlius, 144 reaeted with aeetylene to form 191 and 192 with the initial formation of 193, and with tetramethylethylene to give 194. Other [4 + 2] eyeloadditions of 144 involved those with ethylene, cyelohexene, fra s-stilbene, ethyl vinyl ether, butyl vinyl sulfide, 3-hexyne, and DMAD. 

Add hydrolysis of l-ethylthiobut-l-en-3-yne (143) (10% sulfuric acid, 60-95°C) mainly involves hydration of the triple bond (evidently due to the greater hydrolytie stability of the vinyl sulfide moiety of the moleeule), whieh results in the formation of l-ethylthiobut-l-en-3-one (144). The latter is further hydrolyzed to aeetoaeetie aldehyde (132) (75IZV1975 78IZV153). 

Intermediate 37 can be transformed into ( )-thienamycin [( )-1)] through a sequence of reactions nearly identical to that presented in Scheme 3 (see 22— 1). Thus, exposure of /(-keto ester 37 to tosyl azide and triethylamine results in the facile formation of pure, crystalline diazo keto ester 4 in 65 % yield from 36 (see Scheme 5). Rhodium(n) acetate catalyzed decomposition of 4, followed by intramolecular insertion of the resultant carbene 3 into the proximal N-H bond, affords [3.2.0] bicyclic keto ester 2. Without purification, 2 is converted into enol phosphate 42 and thence into vinyl sulfide 23 (76% yield from 4).18 Finally, catalytic hydrogenation of 23 proceeds smoothly (90%) to afford ( )-thienamycin... 

An explanatory mechanism for the formation of vinyl sulfides is shown in Scheme 24. In route a, (phenylthio)carbene 77 generated from chlorosulfide 75 reacts with the nitrile anion to form (phenylthio)carbanion 79, which then undergoes elimination of cyanide ion to produce vinyl sulfide 76. In route b, 75 reacts first with the nitrile anion 74 to produce P-(phenylthio)nitrile 78 followed by base-catalyzed P-elimination. However, route b is unlikely because 79 cannot be generated from 68 due to a larger pKa value of its ot proton than that of the nitrile. In fact, the reaction of chlorosulfide 75a with lithionitrile 80 gave a different product 81 in 63% yield. 

Another interesting example of a photochemi-cally induced domino process is the combination of the photocyclization of aryl vinyl sulfides with an intramolecular addition as described by Dittami et al. [901 as intermediate a thiocarbonyl ylide can be assumed. The domino-Norrish I-Knoevenagel-allyl-silane cyclization developed by us allows the efficient stereoselective formation of 1,2-trans-subsituted five- and six-membered carbocycles.1911 A photochemical cycloaddition of enamino-aldehydes and enamino-ketones with the intermediate formation of an iminium salt followed by addition to allylsilanes gives access to novel bicyclic heterocy-des. New examples of photochemically induced... 

The iridium-catalyzed hydroboration of heteroatom-containing substrates (vinyl sulfides, sulfoxides, sulfones and sulfonates) was examined by Westcottand Baker [43]. These authors observed the selechve formation of the linear boronate ester... 

The Pummerer reaction of sulfinyl compounds involves the formation of an a-functionalized sulfide [244, 245] from a sulfoxide. Acetic anhydride is commonly used as the electrophile, which adds to the sulfoxide to yield a sulfonium salt, and the rearrangement occurs through successive formations of an ylide (rate-determining step) and an alkylidene sulfonium, trapped by a nucleophile, or stabilized by a proton loss with formation of a vinyl sulfide. 

Recently, the distinction between electrophilic and ion radical (electron-transfer) mechanisms of addition reactions to the vinyl double bond of aryl vinyl sulfides and ethers has been achieved by studying substituent effects (Aplin Bauld 1997). Specifically, the effects of meta and para substituents on the rates of electrophilic addition correlate with Hammett cr values, while ionization of the substrates to the corresponding cation radicals correlates with cr+. The significance of the respective correlations was confirmed by statistical tests. The application of this criterion to the reaction of aryl vinyl sulfides and ethers with tetracyanoethylene revealed that formation of cyclobutanes occurs via direct electrophilic addition to the electron-rich alkene and not via an electron-transfer mechanism. 

Reaction of aryl vinyl ethers, however, invariably gives mixtures of diazetidines and oxadiazines. The ratio is mainly dependent on the nature of the substituent on the phenyl group and, in part, on the nature of the alkyl group of the dialkyl diazenedicarboxylate and the solvent substituents which enhance the nucleophilicity of the alkene and the electrophilicity of the diazene, and polar solvents that favor a polar mechanism, result in concurrent formation of the diazetidine as the predominant product and vice versa15, l< Similarly, diazetidines 7 and oxadiazines 8 are formed in comparable yields in the reactions of vinyl sulfides with dimethyl diazenedicarboxylate, the ratio is principally dependent on the nature of the sulfur substituent (aryl, alkyl)17. 

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