Synthesis and properties of novel helical 3-vinylpyridine polymers containing proline moieties for asymmetric aldol reaction

RSC Advances Pub Date: 2015-06-08 DOI: 10.1039/C5RA07207G

Abstract

Novel optically active polymers containing pendant proline moieties, poly{(?)-L- and (+)-D-proline-[5-(4′-tert-butylphenyl)-3-vinylpyridin-2-yl]amide}, were prepared through radical polymerization of (?)-L- and (+)-D-N-Boc-proline-[5-(4′-tert-butylphenyl)-3-vinylpyridin-2-yl]amide, followed by de-protection of the Boc group. Polarimetry and circular dichroism spectroscopy studies indicated that these polymers took chiral secondary structures. They were employed to catalyze the homogeneous asymmetric aldol reaction of 4-nitrobenzaldehyde with cyclohexanone. The polymeric catalysts showed obviously enhanced reaction rate but slightly reduced enantio-selectivity compared with (?)-L- and (+)-D-proline-[5-(4′-tert-butylphenyl)-3-vinylpyridin-2-yl]amide, the low molar mass counterparts. The lowered enantio-selectivity of the polymeric catalyst might be attributed to the antagonistic action of the configurational chirality of the side-group and the conformational chirality of the polymer backbone on the stereochemistry of aldol reaction.

Graphical abstract: Synthesis and properties of novel helical 3-vinylpyridine polymers containing proline moieties for asymmetric aldol reaction
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