Synthesis of Cinchona Urea Polymers and Their Evaluation as Catalyst in the Asymmetric Reactions

Abstract

Chiral polyureas of cinchona alkaloids were synthesized via repetitive Mizoroki‐Heck (MH) coupling reaction. The Pd‐catalyzed polycondensation of cinchona urea dimers 6 and aromatic diiodide 7 afforded the chiral polyureas (P1−P4). The catalytic activity of the chiral polymers was subsequently investigated. The asymmetric Michael addition of ketoesters to nitroolefins was successfully catalyzed by the polymeric organocatalysts (P1−P4) to give the corresponding Michael adducts with high catalytic activities and excellent enantionselectivities (up to >99% ee). The polymeric catalysts were insoluble in commonly used organic solvents. They were easily recovered and reused several times without any loss of the catalytic activity.

Synthesis of cinchona urea polymers using Yamamoto coupling and their application to asymmetric reaction

“…The various functionalities of cinchona alkaloids can be subjected to a variety of chemical modifications 4–9 . Accordingly, many cinchona alkaloid derivatives have been developed as organocatalysts for asymmetric transformations 10–12 …”

“…[4][5][6][7][8][9] Accordingly, many cinchona alkaloid derivatives have been developed as organocatalysts for asymmetric transformations. [10][11][12] Polymeric organocatalysts have attracted much attention in asymmetric synthesis, largely because they can be easily separated and recovered from their reaction mixtures due to their insolubility, unlike their monomeric counterparts which recovery often requires difficult work-up processes. 12,13 Furthermore, polymeric organocatalysts can be applied in flow reaction systems.…”

Chiral Polyureas Derived Cinchona Alkaloids: Highly Efficient Bifunctional Organocatalysts for the Asymmetric Michael Addition Reaction

“…As a result, we concentrate on cinchona urea derivatives synthesised via the Mizoroki-Heck reaction; there are no other reports of chiral polyureas synthesised via this method than our previous study. [21] In addition to the two-component (MH) coupling of cinchona urea dimers (C6'À OH) with diiodobenzene, we use the self-coupling Mizoroki-Heck reaction of monomers in our design of chiral polyureas. Our current research focuses on chiral polyurea structures in asymmetric catalysis and the assessment of their catalytic efficiency in the asymmetric Michael reaction.…”