Chiral host-guest catalysis : enantioselective epoxidation of unfunctionalized alkenes

TL;DRAbstract

Catalytic asymmetric synthesis is the most effective and challenging approach to obtain enantiomerically enriched organic compounds. This research focused on development of new chiral salen-based macrocyclic catalysts for catalytic asymmetric synthesis, particularly asymmetric epoxidation of unfunctionalized alkenes. -- Template-directed reactions of dialdehydes and (1R.2R)- or (1S.2S)-cyclohexane-1.2- diamine gave three series of macrocyclic salen dimers. A single-crystal X-ray study of the first series. 26-membered macrocycles having -CH₂- links, showed a novel calixarene-like structure with a 1.3-alternate conformation in the solid state. NMR studies revealed that a single conformer was maintained in solution for this series of macrocycles. However, the related 32-membered macrocyclic salen dimer containing longer -(OCH₂)₂- links was flexible and showed four conformers in CDCl₃ at room temperature. -- Sequentially, controlled complexation of the macrocyclic salen dimers afforded mon

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