Vinyl thiol structure

Simulated annealing calculations were performed to acquire the mechanisms of thermolysis of thiirane and thiiranium cation <2002JMT71>. The AMPAC 6.55 package along with AIMl and SAMI methods were used to estimate structures, which were then used as starting points for further ab initio calculations. Critical points were confirmed by calculation of the vibrational frequencies. The primary reactions thiirane 19 —> S-f ethene, thiirane—> vinyl thiol 20, and thiirane ethanethial (thioacetaldehyde) 21 were examined for thermolysis of thiirane Scheme 1. Many secondary reactions were also examined. The simulated annealing method was predicted to be very useful in the future for the study of competing chemical reactions. 

A recently developed application of the Ramberg-Backlund reaction is the synthesis of C-glycosides. The required thioethers can be prepared easily by exchange with a thiol. The application of the Ramberg-Backlund conditions then leads to an exocyclic vinyl ether that can be reduced to the C-nucleoside.95 Entries 3 and 4 in Scheme 10.6 are examples. The vinyl ether group can also be transformed in other ways. In the synthesis of partial structures of the antibiotic altromycin, the vinyl ether product was subjected to diastereoselective hydroboration. 

Peptide thioesters (Section 15.1.10) are generally prepared by coupling protected amino acids or peptides with thiols and are used for enzymatic hydrolysis. Peptide dithioesters, used to study the structures of endothiopeptides (Section 15.1.11), may be prepared by the reaction of peptide nitriles with thiols followed by thiolysis (Pinner reaction). Peptide vinyl sulfones (Section 15.1.12), inhibitors of various cysteine proteases, are prepared from N-protected C-terminal aldehydes with sulfonylphosphonates. Peptide nitriles (Section 15.1.13) prepared by dehydration of peptide amides, acylation of a-amino nitriles, or the reaction of Mannich adducts with alkali cyanides, are relatively weak inhibitors of serine proteases. 

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. 

A wide variety of photoinitiators have been investigated for polymerization of different monomers, such as acrylates, epoxides, vinyl ethers, and thiol-ene monomers. From this point of view, the D-rc-D or A-rc-A chromophores are favored sensitizers if they are combined with a coinitiator [269, 563], The sensitizer excited by TPA can be either oxidized (route A) or reduced (route B) by the coinitiator, depending on the chemical structure of the coinitiator (Fig. 3.64). 

Comparison of relative reactivities at constant steric effects in terms of a few selected Hammett s p values is shown in Table VII for ArS- and in Table VIII for anilines. Although some of the data in Table VII are based only on two points, clearly the p values are structure-dependent. Moreover, these values show no clear trend. The reactivity of P,P-dihalovinyl sulfones are similar to those of the P-halovinyl sulfones, but their p values are much lower. The addition reactions with ArS- show higher p values than for most of the substitutions, but for the structurally similar vinyl sulfones, the p for the substitution is higher. In general, the p values for the anilines are significantly higher, but this fact does not necessarily mean an earlier transition state for the anionic nucleophiles because the p values for the equilibrium acidities of the anilinium ions are higher than those for the thiols. 

Several structurally different diketones (acetylacetone, methyl 2-oxocyclohex-ane carboxylate) and active methylene compounds (diethyl malonate, ethyl aceto-acetate) and thiols (methyl thioglycolate) underwent clean, fast, and efficient Michael addition with methyl vinyl ketone, acrolein, and methyl acrylate over NaY and Na beta zeolites [88] in high yield (70-80%). The reactions were performed in the absence of solvent, at room temperature, with 1 g catalyst per mmol donor. When HY zeolite was used instead of NaY formation of the desired Michael adduct was low and polymerization of Michael acceptor was the main reaction. 

In this chapter, two new approaches for the synthesis of metal-polymer nanocomposite materials have been described. The first method allows the preparation of contact-free dispersions of passivated gold clusters in polystyrene, and it is based on a traditional technique for the colloidal gold synthesis—that is, the alcoholic reduction of tetrachloroauric acid in presence of poly(vinyl pyrrolidone) as polymeric stabilizer. The primary function of the stabilizer is to avoid cluster sintering, but it also allows us to isolate clusters by co-precipitation. It has been found that the obtained polymer-protected nanometric gold particles can be dissolved in alkane-thiol alcoholic solutions to yield thiol-derivatized gold clusters by thiol absorbtion on the metal surface. Differently from other approaches for thioaurite synthesis available in the literature, this method allows complete control over the passivated gold cluster structure since a number of thiol molecules can be equivalently used and the... 

So far, the more common ways to use Pummerer chemistry have been described (i.e., 24 26 and 24 25, Scheme 20.7T However, even if it usually is the A fragment fScheme 20.7 of the sulfoxide which is the inportant component of the target, some researchers have used the classical Pummerer reaction to obtain thiols or complex vinyl sulfides (24 28 or 24 27, Scheme 20.7). Clearly, the convenience of using Pummerer chemistry in the synthesis of thiols is closely related to the structure of the desired product. Sinple thiols can be obtained by Pummerer reactions, but in most cases, other shorter and cheaper methods are available. Consequently, the use of the Pummerer rearrangement to produce thiol products is most favorable in the s)mthesis of very complex thiols. 

Keywords Acrylates Crosslinking Dual cure Epoxides Glass laminates Interpenetrating polymer networks Isocyanates Photo initiated cationic polymerisation Photoinitiators Photopolymerisation Pressure sensitive adhesives Release coatings Structural adhesives Thiol/polyene UV radiation curing Vinyl ethers. 

TEP involves a stoichiometric reaction of a multifunctional olefin and a multifunctional thiol (e.g. thiol-vinyl ether, thiol-allyl ether, thiol-acrylate and thiol-yne). The reaction is a step-growth addition of the thiol to the double bond [1.46a]-[ 1.46c] formation of a thiyl radical, addition of the thiyl to the ene structure, regeneration of a thiyl, etc. termination occurs through recombination and disproportionation reactions. 

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