Vinyl thioacetate

The radical copolymerization of vinyl thioacetate and vinyl thiobenzoate has also been investigated. Overall, the polymerization rate of vinyl thioacetate was smaller than that of vinyl acetate, but its reactivity in copolymers was larger. This has been attributed to the participation of a d-n interaction of the sulfur groupings with the vinyl moiety [87]. 

Coatings, cation-exchange resins Vinyl thioacetate Britain 585,755 1947 Imperial Chemical... 

Poly(vinyl sterate-co-MA), 276 Poly(A >vinylsuccinimide-alt-MA), 335, 399, 400 Poly(vinylsulfonic acid), 287 Poly(vinylsulfonic acid-alt-MA), 660 Poly(vinylsulfonic acid-co-MA), blood anticlotting agent, 287 Poly(vinyl thioacetate-co-MA), 660 Poly(vinyl thiophene-co-MA), 387 Poly(vinyl toluene-alt-MA), 270, 660 Poly(vinyl toluene-co-MA), 270 aluminum alkoxide compositions, 273 Poly(vinyl trialkoxysilanes-co-MA), applications, 454, 660... 

The addition reactions of alkyllithium-lithium bromide complexes to a-trimethylsilyl vinyl sulfones that have as a chiral auxiliary a y-mono-thioacetal moiety derived from ( + )-camphor are highly diastereoselective. A transition state that involves chelation of the organolithium reagent to the oxygen of the thioacetal moiety has been invoked. The adducts are readily converted via hydrolysis, to chiral a-substituted aldehydes22. 

Part C of the present procedure illustrates a mild method for effecting the elimination of thiophenol from thioacetals and thioketals under essentially neutral conditions. The reaction of simple thioacetals and thioketals with bis[copper(I) trifluoro-methanesulfonate] benzene complex in benzene-tetrahydrofuran at room temperature affords vinyl sulfides in high yield (Table I). The reaction presumably occurs by coordination of the thiophilic copper(I) reagent with sulfur, heterolysis to a phenylthio-stabilized... 

The reaction of crotonaldehyde and methyl vinyl ketone with thiophenol in the presence of anhydrous hydrogen chloride effects conjugate addition of thiophenol as well as acetal formation. The resulting j3-phenylthio thioacetals are converted to 1-phenylthio-and 2-phenylthio-1,3-butadiene, respectively, upon reaction with 2 equivalents of copper(I) trifluoromethanesulfonate (Table I). The copper(I)-induced heterolysis of carbon-sulfur bonds has also been used to effect pinacol-type rearrangements of bis(phenyl-thio)methyl carbinols. Thus the addition of bis(phenyl-thio)methyllithium to ketones and aldehydes followed by copper(I)-induced rearrangement results in a one-carbon ring expansion or chain-insertion transformation which gives a-phenylthio ketones. Monothioketals of 1,4-diketones are cyclized to 2,5-disubstituted furans by the action of copper(I) trifluoromethanesulfonate. ... 

Vinyl Sulfides from Thioacetals with Copper Trifluoromethanesulfonate ... 

The temperature at which elimination of thiophenol occurs depends on the substituents on the sulfur-bearing carbon. Thioke-tals react rapidly at 25°. In some cases the elimination of thiophenol from the less reactive thioacetals may also be performed at 25°. However, in the present case the combined inductive effects of the vinyl and methoxy groups evidently destabilize the incipient car-bonium ion and necessitate a higher temperature for the reaction. 

Poly(vinyl alcohol) was tosylated in anhydrous pyridine at 85°C and then reacted with dithiothreitol potassium thioacetate and stirred overnight. The mixture was then reacted with dithiothreitol at ambient temperature to form poly(vinyl alcohol)-g-dithiothreitol. It was hydrolyzed by methanolysis and the thiol macromer isolated. 2... 

Some strategies used for the preparation of support-bound thiols are listed in Table 8.1. Oxidative thiolation of lithiated polystyrene has been used to prepare polymeric thiophenol (Entry 1, Table 8.1). Polystyrene functionalized with 2-mercaptoethyl groups has been prepared by radical addition of thioacetic acid to cross-linked vinyl-polystyrene followed by hydrolysis of the intermediate thiol ester (Entry 2, Table 8.1). A more controllable introduction of thiol groups, suitable also for the selective transformation of support-bound substrates, is based on nucleophilic substitution with thiourea or potassium thioacetate. The resulting isothiouronium salts and thiol acetates can be saponified, preferably under reductive conditions, to yield thiols (Table 8.1). Thiol acetates have been saponified on insoluble supports with mercaptoethanol [1], propylamine [2], lithium aluminum hydride [3], sodium or lithium borohydride, alcoholates, or hydrochloric acid (Table 8.1). 

These methods were extended to 0-hydroxy orthothioesters and p-hydroxy thioacetals [438], leading to ketenethioacetals and vinyl sulfides. With secondary alcohols (R2 - H) a side reaction, which can become preponderant when SOCl2 is used instead of P2I4 in the elimination step, was observed a rearranged product (R2 = SMe in the olefin) was formed. 

Cinchona alkaloids and their derivatives have been reported to catalyse the Michael addition of (V-heterocycles, such as benztriazole, to nitroalkenes in moderate to high enantioselectivities (<94% ee) 15 The thiourea derivative (149) catalysed Michael addition of thioacetic acid to a range of frafts-/f-nitrostyrenes to afford RCH(SAc)- CH2NO2 (<70% ee) 16 The thiourea derivative (149) and its congeners have been identified as efficient organocatalysts for the Michael addition of a-substituted cyano-acetates RCH(CN)C02Et to vinyl sulfones CH2=C(R)S02Ph (72-96% ee) 17 ... 

Vinyl ethers undergo all of the expected reactions of olefinic compounds plus a number of other reactions. For example, vinyl ethers react with alcohols give acetals. The acetals are stable under neutral or alkaline conditions and are easily hydrolyzed with dilute acid after other desired reactions have occurred. Reaction of a vinyl ether with water gives acetaldehyde and the corresponding alcohol and reaction of vinyl ethers with carboxylic acids gives 1-alkoxyethyl esters and with thiols gives thioacetals. 

Peptide aldehydes constitute a rather general example of protease inhibitors. The electrophilic carbonyl group is attacked reversibly by the cleaving nucleophile, forming a covalent acetal or thioacetal intermediate. With cysteine proteases the preferred inhibitors are strong electrophiles, for example ketones, chloromethyl ketones, epoxides, or vinyl sulfones. Many cysteine protease inhibitors form an enzyme-inhibitor complex irreversibly these are therefore denoted suicide-inhibitors . 

Pivaloyloxymethyl (Pom) esters are useful as prodrugs of penicillin and other 0-lactam antibiotics owing to their easy hydrolysis in vivo by ubiquitous non-specific esterases. Mascaretti and co-workers showed that Pom esters can also by cleaved under mild conditions with 2 equivalents of bis(tri-/i-butyltin)oxide as shown in Scheme 6.32. The intermediate tributylstannyl esters are readily hydrolysed on treatment with water to release the carboxylic acid. Functional groups such as aldehydes, thioacetals, amides, vinyl bromides, and nitro compounds are compatible.22... 

N-Vinylpyrrole-2-carbaldehydes 157 were selectively thiylated with ethanethiol either at the aldehyde (acid catalysis) or vinyl group (free-radical initiation) to afford in high to excellent yields N-vinylpyrrole-2-carbaldehyde thioacetals 167 (88-99%) and l-(2-ethylthioethyl) pyrrole-2-carbaldehydes 168 (68-89%), respectively (Equation (52)) (07S452). 

Another advantage over other Lewis acids is the thiophilic nature of copper this has led to its utility in the hydrolysis of thioacetals. Copper(II) chloride in conjunction with copper(II) oxide was introduced by Mukaiyama [16] for the deprotection of 1,3-dithianes and this method has found utility in a variety of synthetic protocols (Sch. 6) [17]. This combination, in which copper oxide plays the role of a buffer to prevent the medium from becoming too acidic, has also found application in the hydrolysis of a-heteroatom substituted and vinyl sulfides [18]. Acetals, which are prone to epimerization under acid-catalyzed hydrolysis conditions (21), can be con-... 

The vinylogous thioacetal 33 was transformed into the a,(8-unsaturated ketone 34 upon CuOTf-mediated hydrolysis whereas the HgCl2-promoted reaction was less effective (Sch. 9) [27]. Similarly, vinyl sulfide 35, which bears an allylic alcohol, was converted into the aj3-unsaturated ketone 36 with complete regiocontrol [28]. This regioselectivity is not dependent upon the heteroatom because the vinyl ether 37 hydrolyzes to the aldehyde or ketone 38 [29]. 

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