Alginate- and κ-carrageenan-supported asymmetric organocatalysts: preparation, characterization, and catalytic activity for Friedel–Crafts alkylation

Abstract

Alginate- and κ-carrageenan-supported imidazolidinone catalysts were newly prepared, and their catalytic activities for the Friedel–Crafts alkylation of 1-methylindole with crotonaldehyde were evaluated. The enantiomeric excess of the product was enhanced by using the polymer-supported catalysts consisting of an appropriate absolute configuration of imidazolidinones and alginate/κ-carrageenan via the cooperative effect that constructs a chiral environment more suited for asymmetric induction compared to imidazolidinone only. Further, the polymer-supported catalysts were easily removed from the reaction media by a simple filtration technique. κ-Carrageenan-supported catalysts were superior in terms of reusability compared to alginate-supported catalysts, likely due to the strong ionic interaction between the sulfate and ammonium moieties.