Polymer Supported Proline-Based Organocatalysts in Asymmetric Aldol Reactions: A Review

The use of proline-based organocatalysts has acquired significant importance in organic synthesis, especially in enantioselective synthesis. Proline and its derivatives are proven to be quite effective chiral organocatalysts for a variety of transformations including the aldol reaction, which is considered as one of the important C-C bond forming reactions in organic synthesis. The use of chiral organocatalysts has several advantages over its metal-mediated analogues. Subsequently, a large number of highly efficient proline-based organocatalysts including polymer-supported chiral analogues have been identified for aldol reaction. The use of polymer-supported organocatalysts exhibited remarkable stability under the reaction conditions and offered the best results particularly in terms of its recyclability and reusability. These potential benefits along with its economic and green chemistry advantages have led to the search for many polymer-supported proline catalysts. In this review, recent developments in exploring various polymer immobilized proline-based chiral organocatalysts for asymmetric aldol reactions are described.

Rongalite-Induced Transition-Metal and Hydride-Free Reductive Aldol Reaction: A Rapid access to 3,3´- Disubstituted Oxindoles and Its Mechanistic Studies

A transition-metal and hydride-free reductive aldol reaction has been developed for the synthesis of biologically active 3,3´-disubstituted oxindoles from isatin-derivatives using rongalite. In this protocol, rongalite plays the dual role...

Chiral Ionic Liquids Based on L-Cysteine Derivatives for Asymmetric Aldol Reaction

Structure, and consequently properties, of ionic liquids can be easily tailored by changing cation/anion combinations and/or attaching functional groups. By grafting enantiopure moieties to the framework of ionic liquid it is possible to prepare bioinspired chiral molecules that can serve as a reaction medium, additive or even asymmetric catalyst. In this context, new chiral ionic liquids (CILs), based on biomolecules, such as aminoacids (L-cysteine derivatives), have been synthesised and tested in asymmetric aldol condensation of aldehydes and ketones. The best results were obtained for CILs composed of S-methyl-L-cysteine cation and bis(trifluoromethane)sulfonimide anion, in the reaction of 2- or 4-nitrobenzaldehyde with acetone or cyclohexanone, giving the aldol product in moderate yields 70–76% and high ee values (up to 96%).

Effect of the Wells–Dawson phosphomolybdic heteropolyacid on the conversion of glucose into glycolic acid

The Wells–Dawson phosphomolybdic heteropolyacid had high activity and selectivity in the epimerization of glucose into mannose and the [2 + 4] retro-aldol reaction of glucose/mannose.

Catalytic properties of 4,5-bridged proline methano- and ethanologues in the Hajos–Parrish intramolecular aldol reaction

The catalysis of the Hajos–Parrish reaction by cis- and trans-4,5-ethano-proline was explored experimentally and computationally with DFT (ωB97X-D and MN15) and DLPNO-CCSD(T).

UV Light-Driven Asymmetric Vinylogous Aldol Reaction of Isatins with 2-Alkylbenzophenones and Enantioselective Synthesis of 3-Hydroxyoxindoles

Chiral 3-hydroxyoxindoles are biologically important molecular motifs which frequently present in natural products and artificial compounds. Herein, we report an ultraviolet light-driven asymmetric vinylogous aldol reaction between versatile isatins and...

NMR relaxation time measurements of solvent effects in an organocatalysed asymmetric aldol reaction over silica SBA-15 supported proline

Immobilisation of organocatalysts onto solid supports represents a very promising solution to tackle their low productivity by enabling their reuse. Herein, the use of NMR relaxation measurements, coupled with reaction...