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The concept of prochirality leads to the nomenclature of the individual faces of a molecule and plays a crucial role in the enantioselective reaction. It is a concept where two or more achiral molecules react to produce chiral products. A typical process is the reaction of an achiral ketone to generate a chiral alcohol. Here, the achiral reactant reacts with an achiral reducing agent, sodium borohydride, to generate an equimolar mixture of the chiral enantiomers of the product. For example, an...
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An Anion-Switchable Dual-Function Rotaxane Catalyst.

I-Cheng Tseng1, Min-Xuan Zhang1, Shih-Lun Kang1

  • 1Department of Chemistry and Center for Emerging Material and Advanced Devices, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, Taiwan.

Angewandte Chemie (International Ed. in English)
|September 6, 2023
PubMed
Summary

This study demonstrates a rotaxane catalyst that switches anion types to selectively catalyze different chemical reactions. This anion switching enables precise control over Michael adduct and thioacetal formation from a single reaction mixture.

Keywords:
Anion ControlCatalysisMichael AdditionRotaxanesThioacetalation

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Area of Science:

  • Supramolecular Chemistry
  • Catalysis
  • Organic Synthesis

Background:

  • Rotaxanes are mechanically interlocked molecules with potential applications in catalysis.
  • Controlling catalytic activity through external stimuli is a key challenge in chemistry.

Purpose of the Study:

  • To develop a rotaxane catalyst with switchable anion binding.
  • To achieve selective catalysis of distinct organic reactions by manipulating the catalyst's anion.
  • To demonstrate the selective formation of Michael adducts and thioacetals.

Main Methods:

  • Synthesis and characterization of a rotaxane catalyst.
  • In situ anion exchange using chloride (Cl-) and tetrakis(pentafluorophenyl)borate (TFPB-) anions.
  • Monitoring catalytic activity for the reaction of trans-cinnamaldehyde with aliphatic thiols.

Main Results:

  • Anion exchange in situ switched the rotaxane catalyst's active sites.
  • Chloride anions exposed dialkylammonium stations for thioacetal formation.
  • TFPB- anions exposed imidazolium stations, catalyzing Michael adduct formation.
  • Selective catalysis was achieved by controlling the associated anion.

Conclusions:

  • The rotaxane catalyst offers a method for orthogonal chemical transformations.
  • Anion-controlled switching provides a versatile platform for selective catalysis.
  • This approach enables the synthesis of complex molecules from simple precursors.