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, RuCl₂(PCy₃)₂CHPh, 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, RuCl₂(3-BrPy)₂(ImMesH₂)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.