Highly active polymeric organocatalyst: Chiral ionic polymers prepared from 10,11‐didehydrogenated cinchonidinium salt

Abstract

Since few examples of 10,11-didehydrogenated (3ethynyl) cinchona alkaloids have been utilized as organocatalysts in asymmetric reaction, we synthesized 10,11-didehydrogenated cinchonidine. The 3-vinyl group of cinchonidine was transformed into a 3-ethynyl functionality. Based on the resulting 10,11-didehydrogenated cinchonidine, the corresponding quaternary ammonium salt and its dimers were prepared. The ion-exchange reaction between the quaternary ammonium salt and sodium sulfonate produced the quaternary ammonium sulfonate as a stable ionic compound. Chiral ionic polymers were then synthesized by the ion-exchange polymerization of the 10,11-didehydrogenated cinchonidinium salt dimer and a disulfonate. The chiral ionic polymers were found to be capable of efficiently catalyzing the asymmetric alkylation of N-(diphenylmethylene)glycine tert-butyl ester. The enantioselec-tivities obtained with the polymeric catalysts were higher than those obtained with the corresponding monomeric catalyst. Dimers of 10,11-didehydrogenated cinchonidinium salts were prepared. Treatment of the dimer with disodium disulfonate gave the chiral ionic polymers, which showed high catalytic activity in asymmetric benzylation of N-(diphenylmethylen)glycine tert-butyl ester. The polymeric catalysts were reused several times without the loss of catalytic activity.

Chiral catalysts immobilized on achiral polymers: effect of the polymer support on the performance of the catalyst

“…Main chain supported chiral salts immobilised by completely ionic interaction, combining both ionic and covalent bonds or just solely based on covalent immobilisation have been successfully obtained. [366][367][368][369][370] A wide range of structural building blocks have been evaluated in order to optimise the supported catalyst. In most of the cases, it has been possible to adjust the polymer structure to obtain catalysts (286)(287)(288)(289) which are often more selective than the homogeneous analogues.…”

Reusable Glucose-Based Crown Ethers Anchored to PVC

“…Throughout the investigation of different phase-transfer catalytic systems, we found that 13 was effective in a three-phase Michael addition of diethyl acetamidomalonate (24) to nitrostyrene (23) (46% ee, Scheme 7). Thus, the native crown ethers (1-3) and the immobilized catalysts (13)(14)(15)(16) were evaluated in this Michael addition (Tables 1 and 2). The results of the reactions with macrocycles 1-3 showed that a higher concentration of the substrate (0.33 M instead of 0.1 M) was favorable.…”

“…Over the past few decades, numerous methodologies have been developed for the attachment of organocatalysts (e.g., proline, squaramide or thiourea derivatives) to various solid supports, including silica, polystyrene resin, or nanoparticles [7]. On the field of phase-transfer catalysis, several research groups bound cinchona alkaloid-based quaternary ammonium salts to polymers (e.g., to polystyrene or polyethylene glycol) [8][9][10][11][12][13][14][15][16]. In the case of the first derivatives, the alkaloid unit was directly connected to the polymer framework, while in the case of the second-generation catalysts it was recognized that if a spacer is used between the polymer and the active center of the catalyst, the selectivity can be improved.…”

Ionic, Core-Corona Polymer Microsphere-Immobilized MacMillan Catalyst for Asymmetric Diels-Alder Reaction

“…For the immobilization of method, we developed an ionic immobilization method for chiral organocatalysts, such as MacMillan catalyst and cinchonidinium, via neutralization reaction or ion-exchange reaction with sulfonated polymers [39,40]. The ionic immobilization methodology has been applied for the synthesis of the main chain of chiral polymers, many of which were prepared by intermolecular reactions of chiral organocatalyst dimers with disulfonic acid derivatives [41][42][43][44][45][46].…”