Bisthioxanthylidene biscrown ethers as potential stereodivergent chiral ligands

Edzard M. Geertsema, Anne Marie Schoevaars, Auke Meetsma, Ben L. Feringa*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

6 Citations (Scopus)
42 Downloads (Pure)

Abstract

The concept of bisthioxanthylidene biscrown ethers as potential stereodivergent chiral ligands in asymmetric synthesis is introduced. Substituted bisthioxanthylidenes may be chiral and can exist as stable enantiomers due to their folded structure. As a result, both a right-handed helix (P) and left-handed helix (M) are present in this type of molecule. This offers the unique possibility to construct two crown ether moieties, attached to the same molecule, of which one exhibits (P)-helicity and the other (M)-helicity. When the crown ether moieties differ in size they can be complexed selectively with a base containing a cation of appropriate diameter. In this manner the (P)-helix and the (M)-helix can be activated selectively to serve as a chiral environment for base catalyzed asymmetric synthesis. Thus, we envisioned the new concept of a single chiral ligand to separately synthesize two enantiomers of a chiral product just by varying the added base. For this purpose, four new bisthioxanthylidene monocrown ethers and two new bisthioxanthylidene biscrown ethers were synthesized. Two biscrowns and two monocrowns were separated into their respective enantiomers (HPLC) and optical data (UV and CD) were collected to ensure stability of enantiomers at ambient temperatures. Ion complexation of one mono- and two biscrown ethers with potassium and sodium cations was investigated.

Original languageEnglish
Pages (from-to)4101-4112
Number of pages12
JournalOrganic & Biomolecular Chemistry
Volume4
Issue number22
DOIs
Publication statusPublished - 2006

Keywords

  • OVERCROWDED ALKENES
  • MACROCYCLIC POLYETHERS
  • ASYMMETRIC-SYNTHESIS
  • CROWN ETHERS
  • COMPLEXES
  • BINDING
  • THERMOCHROMISM
  • DIXANTHYLENES
  • RESOLUTION

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