Azlactone-functionalized smart block copolymers for organocatalyst immobilization. (November 2019)

• Record Type: Journal Article
• Authors: Yu, Xiaoqian; Herberg, Artjom; Kuckling, Dirk
• Is Part Of: European polymer journal. Volume 120(2019)
• Publication Date: 2019-11
• Subjects: Organocatalyst -- Immobilization -- L-proline -- Azlactone -- Block copolymer -- RAFT polymerization -- Aldol reaction; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; Polymerization; Polymers; Periodicals; Electronic journals; 547.705
• DOI: 10.1016/j.eurpolymj.2019.08.034
• Languages: English
• ISSNs: 0014-3057

Abstract

Graphical abstract: Highlights: A temperature-sensitive block copolymer with azlactone moieties was synthesized. Different L -proline derivatives bearing primary amino groups were synthesized. Immobilization of the organocatalysts on the polymer via azlactone click chemistry. Catalyst efficiency and reusability were proven in an asymmetric aldol reaction. Abstract: Nucleophilic ring-opening reaction of azlactone moieties was used for the immobilization of organocatalysts on smart block copolymers. Copolymerization of N -isopropylacrylamide with 2-vinyl-4, 4-dimethylazlactone using a PEG-based macro-RAFT agent afforded temperature-sensitive block copolymers bearing azlactone side groups. Three different organocatalysts possessing primary amino groups were synthesized on the basis of L -proline and L -prolineamide using standard peptide coupling procedures. Organocatalyst immobilization was achieved using a post-polymerization reaction of the primary amino group with the azlactone moiety. The organocatalyst-functionalized block copolymers exhibited a temperature induced self-aggregation upon exceeding a critical phase transition temperature. The block copolymer aggregates with the immobilized organocatalyst in the core were subjected to the aldol reaction of cyclohexanone and p -nitrobenzaldehyde in water. Good diastereo- and enantioselectivities were observed, particularly for the immobilized prolineamides. Organocatalyst separation and reusability was demonstrated for five reaction cycles with no loss in catalyst reactivity. Finally, the applicability of the immobilized organocatalyst to the aldol reaction of cyclohexanone with differently substituted benzaldehydes in water was shown.