New hydroxyproline based methacrylic polybetaines: Synthesis, pH sensitivity and catalytic activity

Polymer‐Supported Chiral Organocatalysts: Synthetic Strategies for the Road Towards Affordable Polymeric Immobilization

“…[41b,41c] conversion, but poorer selectivity than 49. [44] For our acrylic polymer beads, the presence of a spacer seemed to have a surprisingly small effect on enantioselectivity, but slightly more on the diastereoselectivity.…”

“…We had very little success with the use of linear high-load homopolymers (48)(49) in organocatalytic test reactions, but others have reported that homopolymers 49 and 50 provided good conversion (up to 80-100 %) and medium to high enantioselectivity (up to 88 % ee) in intermolecular aldol reactions of 4-nitrobenzaldehyde and 2,2-dimethyl-1,3-dioxan-5-one in DMF. [44] Homopolymer 50 showed better Scheme 10. Polymer-supported prolines by suspension copolymerization of functional methacrylates.…”

“…[43] Shortly after and independently of ourselves, the research groups of Fernández-Mayoralas and Gallardo prepared analogous methacrylic derivatives, using the more traditional chemistry outlined in Scheme 8. [44] Both a small methacrylate (44), the free amino acid of our hydrochloride 41, and aminohexanol-derived proline 47 were prepared. We found acrylic derivative 40 to be very unstable in free form, [41a,41b] presumably because of conjugate addition, so methacrylic esters are definitely preferred as building blocks for copolymerization strategies.…”

“…[44] crosslinked beaded polymer products are available (Figure 4). [41,44] Also, because of the chemical tolerance and experimental simplicity of suspension polymerization, these preparations are easily undertaken on Ͼ10 g scale and as such are much more scalable than the post-modification strategies. [41] Figure 4.…”

“…Polymerization of functional (meth)acrylates. [41,44] www.eurjoc.orgFor all polymeric immobilizations of proline, the use of trans-4-hydroxy--proline as starting material has the profound shortcoming in that its enantiomer is not readily available as it requires the inversion of two stereocenters.…”