Abstract
A number of chiral macrocyclic compounds have been prepared that contain a monosaccharide-derived sub-unit. These sugar-based crown ethers were used as chiral phase transfer catalysts in a few asymmetric reactions. A few of them proved to be effective catalysts in Michael additions, a Darzens condensation and an epoxidation of α,β-enones. It was found that the type of the monosaccharide, the substituents on the sugar unit and on the nitrogen atom of the macroring have a significant influence on both the yield and the enantioselectivity.
Highlights
The synthesis and investigation of sugar-based crown ethers was an interesting and up to date topic in the last decades at our department
The basis of our research is the finding that the chiral crown ethers incorporating monosaccharide moiety in their ring, are able to generate asymmetric induction as chiral phase transfer (PT) catalysts in certain reactions
We have synthesized a variety of chiral crown ethers containing one sugar unit in annelation with the macrocyclic ring from various monosaccharides such as d-glucose, d-mannose, d-galactose, d-altrose, 2-deoxy-d-ribo-hexopyranoside, l-arabinose and from sugar alcohols as l-treitol, d-mannitol
Summary
The synthesis and investigation of sugar-based crown ethers was an interesting and up to date topic in the last decades at our department. The basis of our research is the finding that the chiral crown ethers incorporating monosaccharide moiety in their ring, are able to generate asymmetric induction as chiral phase transfer (PT) catalysts in certain reactions. Crown ethers with carbohydrate moieties form a special group of the chiral PT catalysts. Sugars are suitable source of chirality and their basic chemistry is well explored. They are available in enantiomerically pure form with known chiroptical properties. Crown ethers containing a sugar unit incorporated in the macrocyclic ring may be built from various monosaccharides; macrocycles of different chirality are available [4,5]
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