Glucose-based Ionic Liquid Organocatalysts for Asymmetric aza-Diels-Alder Reactions

Abstract

Carbohydrate-based ionic liquids and salts (CHILS) have recently emerged as an uprising sub-class of ionic liquids. Their starting materials are available in abundant natural resources from plants and fauna. Carbohydrates are not only sustainable; they also exhibit natural chirality. To use this, novel glucosyl imidazolium NTf₂ ionic liquids were synthesized and applied as organocatalysts in aza-Diels-Alder reactions in this work, where we used aldimines and Danishefsky's diene as substrates. We investigated the structure-activity relationships of these glucosyl imidazolium NTf₂ organocatalysts through several functionalizations on the carbohydrate and the imidazole and compared them with common metal catalysts and ionic liquids. Our organocatalysts improved the yield of the model aza-Diels-Alder reaction highly and also had a positive effect on the overall diastereomeric excess.