Vinyl group, thiol addition

Oxidation sometimes gives the carboxylic acid, but the use of hydrogen peroxide (as with other free radical initiators) causes polymerization. Under the influence of radical initiators it is possible to induce thiols to add in an anti-Markownikov manner across an -vinyl group (Scheme 139), while ionic catalysts promote normal electrophilic addition <75CHE1416). 

Amines or sulfides by Michael addition of amines or thiols to vinyl groups... 

Aliphatic polysulfides with two or more carbon atoms per monomeric unit are accessible through ring opening polymerization of cyclic sulfides or by the addition of thiol groups onto vinyl groups. In these cases, the anionic polymerization of cyclic sulHdes differs substantially from that of cyclic ethers. The ethyl anion attacks the carbon atom in cyclic ethers. But in the ethyl lithium initiated polymerization of propylene sulfide, a lithium ethane thiolate is first formed, and its anion then starts the polymerization of propylene sulfide ... 

The radical addition of 2-mercaptoethanol onto oleic acid, from rapeseed oil, has been done by the photochemical generation of radicals without any photoinitiator (20). The 2-mercaptoethanol is photochemically grafted onto vinyl groups of rapeseed oil by a thiol-ene addition to yield polyols. The higher the content of polyunsaturated fatty chains, the lower the rate of 2-mercaptoethanol grafting was found. 

Radical addition of thiol or thiol-modified support to the vinyl group gives the respective thioether linkage 34 and represents one of the most convenient ways to immobilize Cinchona alkaloids [163, 172]. There are also few examples of platinum-catalyzed hydrosilylation of Cinchona alkaloids toward 11-silyl-substituted derivatives 35 with the use of monomeric silanes or polysiloxane polymers [173-175]. De Vries reported rhodium-catalyzed hydroformylation of the four main members of Cinchona alkaloids carried out on a hundred gram scale. Under optimized condition, linear aldehydes 36 were selectively obtained with the yield over 80% [176]. 

Schlaad and coworkers " applied another click reaction for glycoconjugation - the thiol-ene reaction. They first synthesized a well-defined poly[2(-3-isobutenyl)-2-oxazoline] scaffold via cationic ring opening polymerization, which was then followed hy the addition of sugar thiols such as acetylated thioglucose via photoaddition to the polymeric vinyl groups (Figure 2.12). 

Polymer-bound Cinchona alkaloids (53) are catalysts for asymmetric Michael additions of carbanions and thiols to a,j -unsaturated ketones, esters and nitro compounds as shown in Scheme 22. Attachment of the alkaloids to the polymer through the remote vinyl group by copolymerization with acrylonitrile or by addition of a polymeric thiol to the vinyl group was required for catalytic activity and stereoselectivity. " " The enantiomeric excesses attained with the polymeric catalysts (28-51 %) are lower than with the soluble alkaloids (36-63%), but the ease of recovery and reuse of the polymers is usually an advantage. 

In addition to the initiator-controlled polymer functionalization, transfer reactions may result in functional polymers. In free-radical polymerization, thiols are often employed as chain transfer agents. Chain transfer reactions involving thiols proceed via atom abstraction, as illustrated in Scheme 3. Consequently, these molecules do not offer any scope for introducing functionalities at both ends. However, monofunctional telechelics have been successfully prepared by using thiols. For example, Boutevin and co-workers [39,40] introduced polymerizable vinyl groups to polyvinylchloride accord-... 

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