Click reaction thiol-yne

Stereoselectivity of radical addition is not limited to sulfonyl radicals. The (rani-addition has also been observed for tin, bromine, chlorine, and silyl radicals. Varying degrees of selectivity has been observed for addition of carbon-centered radicals, depending on the substituents size and effect on the inversion barrier. Because the importance of negative hyperconjugation decreases for radicals in comparison to the anions, the barriers for inversion decrease in parallel. As a result, the selectivity can erode under conditions when trapping of the radical is slower than the equilibration, e.g. in the thiol-yne click reaction, which often provide a mixture of E and Z-vinyl sulfides. ... 

Scheme 6.17 Radical-mediated mechanism of the thiol-yne click reaction [49]...

In this context, vegetable oils and their fatty acids are key structures because they offer a wide range of possibilities for polymer syntheses based on renewable resources. Thiol-ene and thiol-yne click reactions applied to vegetable oils and their fatty acids constitute a promising strategy to meet those goals. This combination is relatively new and, despite the important contributions achieved, many more are needed. 

SCHEME 8.7 Schematic illustration of the process of ozone prelrealment, graft copolymerization PVDF with PMA, preparation of PVDF-g-PPMA membrane with clickable surface by phase inversion, preparation of functional PVDF-g-P[PMA-cZ/ck-MPS] membranes via surface thiol-yne click reaction of thiols on the PVDF-g-PPMA membrane, and preparation of PVDF-g-P[PMA-c//ck-P-CD] membranes via surface alkyne-azide click reaction on the PVDF-g-PPMA membranes. PVDF, poly(vinylidene fluoride) PMA, propargyl methacrylate MPS, 3-mercapto-l-propanesulfonic acid sodium salt azido-fl-CD, mono(6-azido-6-desoxy)-P-cyclodexIrin. Reprinted with permission from Reference 168. Copyright 2011 American Chemical Society. 

B2) were synthesized. Subsequently, hyperbranched polymers were formed by a thiol-yne click reaction under UV radiation at room temperature, whereby yields over 95% were reached within less than 2 h (Figure 8.9). Furthermore, the reaction was applied to RAFT polymerized linear polymers bearing an alkyne and a thiol group at the a and co end of the polymer, allowing subsequently formed hyperbranched polymer to incorporate additional functionalities. 

A similar active-template strategy was applied by Goldup etal. forthe formation of doubly interlocked [3]rotaxanes [93]. A photochemical thiol-yne click reaction (a variant of thiol-ene click) was used for the formation of rotaxanes, proceeding mildly at ambient temperature and humidity under an air atmosphere [94]. 

There are many reports on azide-alkyne click polymerisation (a subject not discussed in the present chapter) but research on thiol-yne click polymerisation is in its early stages. New reaction types, novel catalyst systems other than those existing (i.e., photon, heat, organic base, transition-metal complexes) and new functionalities of the ensuing polymers are waiting to be developed [51]. 

Only a few studies on oleochemistry have been reported until now. Similar to the effects seen with the thiol-ene reaction, one can take advantage of this interesting tool for the synthesis of novel monomers to be polymerised further by classical methods. Also, the possibility of two thiol groups reacting with one ethynyl group via two-step addition makes thiol-yne click polymerisation an interesting method for the preparation of hyperbranched polymers. 

Describe the main criteria that should be satis ed for a reaction to be called a click reaction How would you justify the inclusion of the following reactions into the pantheon of click reactions (a) Copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reactions (b) strain-promoted azide-alkyne coupling (SPAAC) reactions (c) Diels-Alder (DA) cycloaddition reactions (d) thiol-ene (TE) reactions and (e) thiol-yne (TY) reactions ... 

Similar to the thiol-ene reaction, the thiol-yne reaction is also classified as click. Therefore, it has attracted the attention of many researchers interested in applying more environmentally friendly approaches to their work. 

Click reactions are an attractive means to synthesize SCNPs due to their high efficiency, high functional group tolerance, and mild reaction conditions. Copper-mediated azide-allgme cycloaddition, thiol-ene addition, thiol-yne addition, and amine-isocyanate addition" click reactions have been used to synthesize cross-links and form SCNPs. 

Several other highly efficient coupling reactions have been reported to be of click in nature since they fulfilled all or some of the click chemistry criteria. Several types of metal-free click reactions have been developed. The more prominent ones are thiol-ene, thiol-yne, thiol-para-fluoro, hetero Diels-Alder (HDA) coupling reactions, and pyridyl disulfide exchange reactions (Scheme 8.6) [155-162]. Each of them requires specific initiators, monomers, and/or polymerization conditions. Therefore, the synthetic route should be carefully designed to prepare the desired functional polymers or solid substrates. 

Cu A AC) (Johnson et at, 2008), historically the first one that has been given this name, is up to now the most apphed method. However, despite the popularity of this reaction on a lab scale, its widespread use is limited by the presence of a cytotoxic transition metal and the need for potentially explosive azides. For that reason, a range of copper-ftee click approaches are now intensively studied, including thiol-ene/yne addition reactions and (ultrafast) hetero-Diels— Alder cycloaddition (HDA) reactions, which are believed to have great potential to become as popular as the CuAAC in the click chemistry toolbox (Lutz, 2008 Becer et ai, 2009). 

Various click chemistries, building the foundation for most post-polymerization modifications, have also been applied for fabrication of reactive porous polymer monoliths [118-125]. Click reactions include alkyne-azide, thiol-ene, and thiol-yne reactions, and these reactions can be conducted under mild conditions, unlike many other polymer graft reactions. Svec and coworkers used the thiol-ene reaction to functionalize porous polymer monoliths [121]. Monoliths were thiolated with cysteamine, followed by cleavage of the disulfide bonds using tri(2-carboxylethyl) phosphine to expose the desired thiol groups. Then, lauryl methacrylate monomers were clicked onto the monoliths using either heat or UV initiation. Thiol-yne and... 

In short, the thiol-yne radical click reaction is the formation of a 1,2-dithioether through double addition of thiols on to an alkyne. The reaction has largely been used to generate multifunctional polymer structures. Repetitive thiol-yne reactions are used to form multifunctional molecules, which are further used to make dendrimers [42] or hyperbranched polymers [46]. 

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