Thiol-Michael coupling chemistry: facile access to a library of functional exo-7-oxanorbornenes and their ring-opening metathesis (co)polymerization

Abstract

The nucleophile initiated thiol-Michael reaction of a wide range of mono and multifunctional thiols with a novel acrylic exo-7-oxanorbornene is described. We highlight how this process affords ready access to a large library of thioether-based substrates in a quick and convenient fashion. New substrates containing, for example, ester, fluoro, and siloxy functionality polymerized in a controlled fashion with Grubbs' first generation (G1) catalyst, RuCl 2 (PCy 3 ) 2 CHPh, yielding homopolymers with controlled, predetermined molecular weights and polydispersity indices in the range 1.10-1.31. Other examples containing -OH (alcohol, diols, sugars) and certain heterocyclic functionality could only be polymerized to high conversion in a controlled manner with the Grubbs' third generation catalyst, RuCl 2 (3-BrPy) 2 (ImMesH 2 )CHPh. Examples of copolymers with statistical and block architectures were also prepared yielding well-defined materials with controlled molecular weights and narrow, unimodal molecular weight distributions. Efficient, sequential post-polymerization modification of an AB diblock copolymer bearing protected alkyne and protected sugar functionality afforded access to additional new block copolymers including amphiphilic species as well as a common material susceptible to Cu(I)-catalyzed alkyne-azide coupling. Finally, we show that the common, and key, acrylic functional exo-7-oxanorbornene substrate can, if desired, be directly (co)polymerized with the Grubbs' G1 catalyst yielding (co)polymers containing electron-deficient ene functional groups that can be modified post-polymerization.

Thiol‐Michael coupling and ring‐opening metathesis polymerization: facile access to functional exo‐7‐oxanorbornene dendron macromonomers

“…The primary aim of this work was to evaluate the ability to prepare highly functional, ROMP‐active dendron monomers based on the exo ‐7‐oxanorbornene structural motif employing straightforward thiol‐Michael click chemistry. Given our previous work with thioether‐based monofunctional ROMP‐active monomers and the synthesis of hyperbranched (co)polymers from difunctional substrates, we initially targeted the diacrylate and tetraacrylate functional dendron species G1 and G2 that would serve as common substrates in subsequent nucleophile‐mediated thiol‐Michael reactions. G1 and G2 were prepared via multistep procedures as outlined in Scheme .…”

“…The reaction is rapid, requires very low levels of either amine or phosphine as the initiating species, generally gives quantitative formation of the thiol‐Michael adduct and has been shown to be superior to the more commonly employed base‐mediated thiol‐Michael reaction. Recently, for example, we reported the synthesis of a novel acrylate‐bearing exo ‐7‐oxanorbornene, (2‐((3a R ,7a S )‐1,3‐dioxo‐3a,4,7,7a‐tetra‐hydro‐1 H ‐4,7‐epoxyisoindol‐2(3 H )‐yl)ethyl acrylate), and demonstrated how from this single readily accessible molecule a wide range of monofunctional and difunctional thioether‐based ring‐opening metathesis polymerization (ROMP) active substrates could be prepared quickly via phosphine‐mediated conjugate addition reactions. The resulting thioether adducts were demonstrated to undergo controlled ROMP yielding well‐defined (co)polymers in the case of the monofunctional adducts and hyperbranched (co)polymers for the difunctional species.…”

Non‐Delaminating Polymer Hydrogel Coatings via C,H‐Insertion Crosslinking (CHic)—A Case Study of Poly(oxanorbornenes)

“…Synthesis of Monomer M3 : Step 1 : Synthesis of Z5 (3a,4,7,7a‐Tetrahydro‐2‐(2‐hydroxyethyl)‐4,7‐epoxy‐1H‐isoindole‐1,3(2H)‐dione) . The synthesis was performed as reported in the literature . Exo ‐3,6‐Epoxy‐1,2,3,6‐tetrahydrophthalic acid anhydride ( R1 , 8.3 g, 50 mmol, 1 eq.)…”

Combining Ring‐Opening Metathesis Polymerization and Thiol‐Ene Coupling Chemistries: Facile Access to Novel Functional Linear and Nonlinear Macromolecules

“…As such, one desirable goal in the ROMP arena is the facile access to a suite of functional monomers employing non‐demanding and straightforward chemistry. In an effort to address this issue, Liu et al recently reported the synthesis and (co)polymerization of a library of thioether‐based exo ‐7‐oxanorbornenes obtained employing nucleophilic thiol‐Michael coupling with a common substrate (Scheme ).…”