Vinyl thioether

Typical of these materials are the poly(vinyl thioethers), the poly(vinyl isocyanates), the poly(vinyl ureas) and the poly(alkyl vinyl ketones). Methyl isopropenyl ketone and certain vinylpyridine derivatives have been copolymerised with butadiene to give special purpose rubbers. 

When thiols are added to substrates susceptible to nucleophilic attack, bases catalyze the reaction and the mechanism is nucleophilic. These substrates may be of the Michael type or may be polyhalo alkenes or alkynes. As with the free-radical mechanism, alkynes can give either vinylic thioethers or dithioacetals ... 

The hydrothiolation of terminal alkyl alkynes with 96 (Fig. 2.17) proceeds with good degree of regio- and chemo-selectivity, especially with thiophenol and p-methoxy-thiophenol as substrates. Isomerisation to the internal alkenyl thiolates accounts for less than 9% of the thiolated products under the reaction conditions. In addition, further hydrothiolation of the vinyl thioether product is not observed. Typical conversions of 70-85% at 1 mol% loading at 80°C within 5 h are observed. Arylthiols substituted with electron-withdrawing groups afford lower conversions. 

In Entry 5, the carbanion-stabilizing ability of the sulfonyl group enables lithiation and is then reductively removed after alkylation. The reagent in Entry 6 is prepared by dilithiation of allyl hydrosulfide using n-bulyl lithium. After nucleophilic addition and S-alkylation, a masked aldehyde is present in the form of a vinyl thioether. Entry 7 uses the epoxidation of a vinyl silane to form a 7-hydroxy aldehyde masked as a cyclic acetal. Entries 8 and 9 use nucleophilic cuprate reagents to introduce alkyl groups containing aldehydes masked as acetals. 

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). 

The deprotection of the polyamine-thioethers 40a,b can also be accomplished in similar good yields with Li/naphthalene in THF (214). Cleavage of the thioether functions also commenced with [PdCl2(NCMe)2] in the case of 40b (216), and it is likely that the other macrobicycles will also undergo this metal-ion mediated cleavage reaction as well (Scheme 2). Note that this reaction cleaves only one of the two thioether bonds forming a macrocyclic ligand with one thiophenolate and one vinyl-thioether moiety, as... 

Scheme 6.86 displays the generation of 417 from the cephalosporin triflate 416 and the formulas of the trapping products with ethylene, monosubstituted ethyl-enes, 1,1-disubstituted ethylenes and 1,1-dimethylallene [155], It was shown for two such reaction partners (styrene and phenyl vinyl thioether) that the exchange of the... 

For the addition of ethylene, EtOAc as solvent was particularly advantageous and gave 418 in 60% yield (Scheme 6.86). The monosubstituted ethylenes 1-hexene, vinylcyclohexane, allyltrimethylsilane, allyl alcohol, ethyl vinyl ether, vinyl acetate and N-vinyl-2-pyrrolidone furnished [2 + 2]-cycloadducts of the type 419 in yields of 54—100%. Mixtures of [2 + 2]-cycloadducts of the types 419 and 420 were formed with vinylcyclopropane, styrene and derivatives substituted at the phenyl group, acrylonitrile, methyl acrylate and phenyl vinyl thioether (yields of 56-76%), in which the diastereomers 419 predominated up to a ratio of 2.5 1 except in the case of the styrenes, where this ratio was 1 1. The Hammett p value for the addition of the styrenes to 417 turned out to be -0.54, suggesting that there is little charge separation in the transition state [155]. In the case of 6, the p value was determined as +0.79 (see Section 6.3.1) and indicates a slight polarization in the opposite direction. This astounding variety of substrates for 417 is contrasted by only a few monosubstituted ethylenes whose addition products with 417 could not be observed or were formed in only small amounts phenyl vinyl ether, vinyl bromide, (perfluorobutyl)-ethylene, phenyl vinyl sulfoxide and sulfone, methyl vinyl ketone and the vinylpyri-dines. 

Thiophenols undergo base-catalyzed, Michael addition to acetylenic acids and esters to give trans addition products. These vinyl thioethers have been used in the synthesis of thiochromones. " Recently, Undheim and Lie have shown that thiophenol adds to DMAD with concomitant cyclization to give benzo[6]thiophenes. 

The carbonyl of trifluoroacetates is reactive enough to react with phosphoranes and to yield trifluoromethyl enol ethers (the reaction must be conducted without lithium salts i.e., the phosphorane must be generated without a nonlithiated base). In the same way, trifluoroacetamides and trifluorothioacetates afford, respectively, trifluoromethyl enamines and vinyl thioethers (Figure 2.44). " ... 

In some cases involving aliphatic thiocarbonyl ylides, a 1,4-H shift occurs to afford vinyl thioethers. As an example, thiocarbonyl ylides (41), generated by the addition of isopropylidene carbene to aliphatic thioketones, are converted to divinylthioethers (42) (84) (Scheme 5.16). 

On the other hand, the analogous reaction of 2,2,4,4-tetramethyl-3-thioxocyclo-butanone and 2-diazopropane afforded a stable cycloadduct, which upon heating eliminated N2 and yielded a mixture of thiirane (46) and vinyl thioether 47 (85). A similar competition involving both an electrocyclization and a 1,4-H shift was observed in the case of diisopropylthioketone (5)-methylide (39). 

The intermediates 8 are formed stereoselectively and have the (Z)-configuration. This stereoselectivity has been exploited in syntheses of naturally occurring vinyl thioethers (82JOC374). Other useful synthetic applications of the reaction include those leading to the formation of the cyclic enol... 

Triazines are generally more reactive in [2 + 4] cycloaddition in comparison with 1,2,3-tria-zines. The wide variety of dienophiles can be employed enamines, enaminones, vinyl silyl ethers, vinyl thioethers, cyclic ketene jV,O-acetals, /V-phenylmaleimide, 6-dimethylaminopentafulvene, 2-alkylidene-imidazolidines (cychc ketene aminals), cyclic vinyl ethers, arynes, benzocyclopropene, acetylenes, and alkenes like ethylene, (Z)-but-2-ene, cyclopentene, cyclooctene and bicyclo[2.2.1]hept-2-ene, hexa-1,5-diene, cycloocta-1,5-diene, diallyl ether, cyclododeca-l,5,9-triene,... 

From the synthetic viewpoint, a particularly interesting trifluoroacetylation reaction of simple vinyl ethers was reported first by Hojo et al in 1976 [73] The scope and limitation of this particular reaction were elaborated intensively, the reaction proved to be of general applicability with practically no restrictions on substituents of the vinyl ether moiety 9] (equation 34) This general validity is particularly beneficial because a trifluoroacetylated vinyl ether is the synthetic equivalent of a specifically protected tnfluoromethyl-substituted 1,3-dicarbonyl compound 19], thus the reaction provides access to a broad spectrum of variously substituted synthetic building blocks with selective reactivities on each carbon acceptor (a) and donor (d) center (equation 35) Obviously, such building blocks can react as heterodiene systems m cycloaddition reactions [< 74] or can be treated with a wide variety ot 1,2 or 1 3-dinucleophihc species to give any desired tnfluoromethyl-substituted carbocychc or heterocyclic system [8 75] Treatment of simple vinyl ethers with an excess of trifluoroacetic anhydride at elevated temperature leads to doubly acylated products [76] Comparable acylation reactions occur with vinyl thioethers [73], and the mesoiomc l,3-oxathiol-4-ones show, at least in a formal sense, similar behavior [77] (equation 36)... 

Trost has used vinyl thioethers to add two carbons with terminal functionalization (3). Vinyl ethers and vinyl acetate give mixtures of products while isopropenyl acetate reacts selectively with aryl halides and at least one vinylic halide. 

Azine approach. Cyclization by oxidative formation of the S—N bond is frequently the final step in isothiazole syntheses. This approach can be used in the synthesis of the parent cation from the thioformyl precursor (129). 2-Substituted derivatives would require thioketone precursors and such compounds are more readily available as vinyl thioethers, e.g. (130). Bromine is used for the oxidative cyclization in this instance giving (13lj (73CC150). 

Vinyllithiums of type 663 (R2 = R3 = H) reacted with primary alkyl bromides, carbonyl compounds, carbon dioxide, DMF, silyl chlorides, stannyl chlorides, disulfides and phenylselenyl bromide142,970-979. Scheme 173 shows the synthesis of dihydrojasmone 669 from the corresponding 1,4-diketone. a-(Phenylsulfanyl)vinyllithium 665, prepared from phenyl vinyl thioether, reacted with hexanal and the corresponding adduct 666 was transformed into its acetoacetate. This ester 667 underwent a Carrol reaction to produce the ketone 668, which was transformed into the cyclopentenone 669 by deprotection either... 

Banerjee, S., Das, J., and Santra, S. 2009. Native silica nanoparticle catalyzed anti-Markovnikov addition of thiols to inactivated alkenes and alkynes A new route to linear and vinyl thioethers. Tetrahedron Letters, 50 124—27. 

The asymmetric ene reaction with catalyst 98 is restricted to activated aldehydes as is indicated by the data in Table 16. The rates of the reaction are such that it is not applicable to internal olefins. A variety of 1,1-disubstituted alkenes can be used to give good asymmetric induction with the fastest rates observed with phenyl vinyl thioethers. Turnover can be realized with the more reactive aldehydes and/or alkenes but only in the presence of molecular sieves. The reaction of chloral with a-methyl-styrene shows that higher induction can be achieved with lower temperatures although the reaction is slower. The nature of the solvent affects the rate of the reaction. The reaction is much slower in toluene than in dichloromethane. 

Kobayashi et al. found that lanthanide triflates were excellent catalysts for activation of C-N double bonds —activation by other Lewis acids required more than stoichiometric amounts of the acids. Examples were aza Diels-Alder reactions, the Man-nich-type reaction of A-(a-aminoalkyl)benzotriazoles with silyl enol ethers, the 1,3-dipolar cycloaddition of nitrones to alkenes, the 1,2-cycloaddition of diazoesters to imines, and the nucleophilic addition reactions to imines [24], These reactions are efficiently catalyzed by Yb(OTf)3. The arylimines reacted with Danishefsky s diene to give the dihydropyridones (Eq. 14) [25,26], The arylimines acted as the azadienes when reacted with cyclopentadiene, vinyl ethers or vinyl thioethers, providing the tet-rahydroquinolines (Eq. 15). Silyl enol ethers derived from esters, ketones, and thio-esters reacted with N-(a-aminoalkyl)benzotriazoles to give the /5-amino carbonyl compounds (Eq. 16) [27]. The diastereoselectivity was independent of the geometry of the silyl enol ethers, and favored the anti products. Nitrones, prepared in situ from aldehydes and N-substituted hydroxylamines, added to alkenes to afford isoxazoli-dines (Eq. 17) [28]. Addition of diazoesters to imines afforded CK-aziridines as the major products (Eq. 18) [29]. In all the reactions the imines could be generated in situ and the three-component coupling reactions proceeded smoothly in one pot. 

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). 

The [3-1-2] methylenecyclopentane annulation of [(trimethylsilyl)methylene]-cyclopropane dicarboxylates with unactivated and electron-rich alkenes (vinyl ether, vinyl thioether, or vinyl silyl ether) are efficiently photocatalyzed by butyl disulfide or bis(tributyltin) [78]. 

In certain systems the crown thioether ligand itself may undergo some chemical transformation when coordinated to a metal ion. For example, in mildly basic conditions, [Rh([9]aneS3)2]3+ undergoes deprotonation at an a carbon, with subsequent ring opening to afford the vinyl thioether... 

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