Thiol-Michael addition

Meldrum s Acid-Containing Polymers as Precursor for Ketene Coupling 

Choi et al. [46], EVE ethyl vinyl ether, and (c) cross-linking of the polyacetylene blocks of block copolymer 73 by dimerization of the generated ketene moieties. 

However, only the PS was further modified with a rhodamine dye (TAMRA cadaverine) by spin-casting of the polymer, followed by stamping with the dye and subsequent thermal treatment [45]. Block copolymers (73) via ROMP of 

---

The thiol Michael addition reaction rate increases with pH, connected to the increase of thiolate anion concentration (Rizzi and Hubbell, 2005). The reaction on the polymeric system is shown in Fig. 14.9. 

For thiol-Michael additions, electron-deficient olefins such as acrylates or maleimides are reacted with thiols [36, 44, 49]. While acrylates, owing to their ability to quench the polymerization via cross metathesis (CM) [50-52], are introduced by post-functionalization, maleimide groups are compatible with ruthenium catalysts and can be introduced within the monomer [36, 39]. Nonetheless, monomers with acrylate moieties were used for direct polymerization [43]. 

Scheme 9.10 Thiol-Michael addition on exo-ONBEs and their use homo and copolymerization via ROMP [49].

Scheme 5 One-pot thiolactone-based ctmjugation aminolysis of a thiolactone, followed by thiol-click conjugation. The in situ generated thiol can react according to three distinct reaction pathways (a) radical (UV-initiated) or (b) nucleophilic (thiol-Michael) addition of a thiol to a double bond (thiol-ene), and (c) thiol-disulfide exchange...

Sui X, van Ingen L, Hempenius MA, Vancso GJ (2010) Preparation of a rapidly forming poly (ferrocenylsilane)-poly(ethylene glycol)-based hydrogel by a thiol-michael addition click reaction. Macromol Rapid Corrunun 31 2059-2063... 

Apart from base catalysis, Michael addition of thiols can also be performed using nucleophUic catalysis. Primary and secondary amines and certain phosphines are the most commonly used catalysts. Nucleophile mediated thiol-Michael addition reactions have extensively been studied. The nucleophiles attack the Michael acceptors to generate a carbanion, which abstracts protons from thiols to generate thiolate anions, which in turn propagate the reaction (Scheme 1.16) [56]. NucleophUicity of the catalyst plays a crucial role in the kinetics of the nucleophile-based thiol-Michael addition reactions, as stronger the nucleophile, more easily the thiolate anion will be generated. 

Owing to the low p/C values of thiols, thiol—Michael addition reactions can be performed under ambient conditions in water or other protic solvents. However, both base- and nucleophile-catalyzed thiol-Michael addition reaction are affected to some extent by the presence of external protic species, especially the nucleophUe-mediated pathway is more affected due to low catalytic concentration of nucleophiles compared to bases in these reactions. 

---