Synthesis of core-corona polymer microsphere-supported cinchonidinium salt and its application to asymmetric synthesis

Synthesis of homo- and copolymer containing sulfonic acid via atom transfer radical polymerization

Well-defined functional poly(p-phenyl styrenesulfonate) and poly(p-phenyl styrene-sulfonate-co-styrene) were successfully synthesized by the atom transfer radical polymerization (ATRP) using CuBr/bpy(PMDETA) catalyst and 1-phenylethyl bromide (1-PEBr) as an ATRP initiator in diphenyl ether (DPE) or dimethyl formamide (DMF). In both homo- and copolymers, the CuBr/PMDETA catalytic system in DPE or DME showed higher yield than CuBr/bpy and the polydispersity index (PDI) of polymer was low. Using PMDETA or bpy as a ligand in DMF, the high yield with high PDI was obtained than in DPE. We found that the CuBr/PMDETA catalyzed ATRP of p-phenyl styrenesulfonate and copolymerization with styrene comonomer in DPE proceeded in a controlled manner. The polymers containing sulfonic acid were obtained by the chemical deprotection of protecting group, followed by acidification. The molecular structure, molecular weights and thermal properties of the copolymers were determined by nuclear magnetic resonance (¹H NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively.

Ionic, Core-Corona Polymer Microsphere-Immobilized MacMillan Catalyst for Asymmetric Diels-Alder Reaction

The improvement of the catalytic activity of a heterogeneous chiral catalyst is one of the most critical issues, as are its recovery and reuse. The design of a heterogeneous chiral catalyst, including the immobilization method and the support polymer, is of significance for the catalytic activity in asymmetric reactions. An ionic, core-corona polymer microsphere-immobilized MacMillan catalyst (ICCC) was successfully synthesized by the neutralization reaction of sulfonic acid functionalized core-corona polymer microsphere (CCM–SO3H) with a chiral imidazolidinone precursor. We selected the core-corona polymer microsphere as the polymer support for the improvement of catalytic activity and recovery. The MacMillan catalyst was immobilized onto the pendant position of the corona with ionic bonding. ICCC exhibited excellent enantioselectivity up to 92% enantiomeric excess (ee) (exo) and >99% ee (endo) in the asymmetric Diels-Alder (DA) reaction of (E)-cinnamaldehyde and 1,3-cyclopentadiene. ICCC was quantitatively recovered by centrifugation because of the microsphere structure. The recovered ICCC was reused without significant loss of the enantioselectivity.