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.

Porous Organic Polymer Supported Pd/Cu Bimetallic Catalyst for Heterogeneous Oxidation of Alkynes to 1,2-Diketones

A porous organic polymer (POP-POPh3) was readily prepared by oxidation of POP-PPh3 with H2O2. After coordination with PdCl2 and co-catalyst of CuBr2 precursor, a Pd/Cu bimetals-loaded porous organic polymer (Pd/Cu@POP-POPh3)...

Microwave-assisted oxidative coupling of thiols using polystyrene supported bromoderivatives of 2-oxazolidone

Polymer-supported reagents have become popular in synthetic organic chemistry over the past decades. But the kinetics of polymer-supported reactions is slow compared to solution phase synthesis because of the poor diffusion of the reactants through the macromolecular polymer matrix. This difficulty can be reduced to a great extent by performing polymer-supported reactions under microwave (MW) conditions. The present work is focussed on the design and development of an innovative, powerful, MW stable and recyclable polymeric reagent prepared by attaching bromoderivative of 2-oxazolidone into the macromolecular matrix of polystyrene. 3% cross-linked polystyrene was prepared by free radical aqueous suspension polymerization technique using tetra ethylene glycol diacrylate as the cross-linking agent and the resulting beads were functionalized by chloromethylation followed by reaction with 2-oxazolidone. Bromine functionality is introduced into the polymer by treating with bromine in carbon tetrachloride. The synthetic utility of the prepared polymeric reagent was demonstrated by the oxidative coupling of thiols to disulfides under MW irradiation. No over oxidation was observed in this protocol and the utilization of polystyrene support simplifies work up and product isolation. The synthesised polymeric reagent displayed good cyclic stability up to five cycles without any substantial decrease in bromine content and satisfactory storage stability under normal laboratory condition. Moreover this may be the first report that uses MW energy for the oxidation of thiols to disulfides using polymer-supported reagents. [Formula: see text]