Abstract
We synthesised a library of cis- and trans-cyclic dipeptides and evaluated their efficacy as catalysts in the asymmetric Weitz-Scheffer epoxidation of trans-chalcone. A thorough investigation relying on structure-activity studies and computational studies provided insights into the mechanism of the process. Our results revealed some structural features required for efficient conversion and for introduction of chirality into the product. The cyclic dipeptide acts as a catalyst by templating a supramolecular arrangement at the aqueous-organic interface required for efficient transformations to occur. Among all cyclic dipeptides investigated, cyclo(Leu-Leu) was the most efficient supramolecular catalyst.
Highlights
Numerous reports describe the use of chiral receptors as chirality sources in chemical transformations
2.1 Cyclic dipeptides synthesis We synthesized a library of cyclic dipeptides with a variety of substituents and stereochemistries, by taking advantage of the availability of natural and synthetic amino acids to be chiral synthons
This library will facilitate the study of the structural features required for efficient conversion and enantioselectivity
Summary
Numerous reports describe the use of chiral receptors as chirality sources in chemical transformations. CDPs form highly ordered supramolecular structures such as linear one-dimensional hydrogen-bonded tapes and hydrogen-bonded dimers and multimers. Their properties could be exploited for efficient supramolecular chiral catalysis.[12,13] In addition, Cis CDPs create a concave cavity that could serve as a receptor to bind a substrate in a chiral environment. Along those lines, we recently reported the asymmetric epoxidation of α,βunsaturated ketones in a triphasic system using insoluble CDPs located at the interface. Our studies revealed some important supramolecular and structural features required for efficient conversion and more importantly, to create chiral products
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