A recyclable helical l-Valine-polymer catalyst for highly enantioselective Aldol and oxa-Michael-Aldol cascade reactions

Abstract

A novel helical polymer (poly-1_m) bearing l-Valine pendant was designed and synthesized. The chiral l-Valine polymer catalyst demonstrated excellent catalytic activity and stereoselectivity in the Aldol reaction. The polymer poly-1₂₀₀ catalyzed the Aldol reaction of cyclopentanone and 4-nitrobenzaldehyde in water, achieving an enantiomeric excess (ee) value of up to 97 % and a diastereomeric ratio (dr) of 42/58. Furthermore, the chiral polymer catalyst can be recycled three times in asymmetric Aldol addition reactions without significant loss of catalytic activity. The same catalyst was applied in the asymmetric oxa-Michael-Aldol cascade reaction of cinnamaldehyde and salicylaldehyde, achieving an enantiomeric excess of 87 %.