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Configurational Stability of [5]Helicenes
Prince Ravat1, Rahel Hinkelmann1,2, David Steinebrunner1,3
1Department of Chemistry, University of Basel , St. Johanns-Ring 19, CH-4056 Basel, Switzerland.
Organic Letters
|July 1, 2017
Summary
Difunctionalized [5]helicenes exhibit high configurational stability, with dimethyl derivatives showing exceptional stability comparable to larger helicenes. This study reveals an exponential correlation between torsional twist and enantiomerization energy.
Area of Science:
- Organic Chemistry
- Stereochemistry
- Photochemistry
Background:
- Helicenes are chiral aromatic hydrocarbons with unique helical structures.
- Configurational stability is crucial for applications in chiral recognition and materials science.
- Understanding structure-stability relationships in helicenes informs the design of novel molecular architectures.
Purpose of the Study:
- To synthesize and characterize difunctionalized [5]helicenes.
- To investigate the impact of fjord-region substituents (fluoro, methoxy, methyl) on configurational stability.
- To compare the stability of difunctionalized [5]helicenes with their monofunctionalized analogues and parent [5]helicene.
Main Methods:
- Photochemical synthesis and benzylic coupling.
- Resolution of enantiomers.
- Determination of Gibbs activation energies of enantiomerization (ΔG⧧(T)).
Main Results:
- All synthesized difunctionalized [5]helicenes demonstrated high configurational stability.
- An exponential correlation was identified between torsional twist and ΔG⧧(T).
- The dimethyl derivative displayed exceptional stability, rivaling that of [9]helicene.
Conclusions:
- Fjord-region difunctionalization enhances the configurational stability of [5]helicenes.
- Torsional twist is a key factor governing enantiomerization energy in helicenes.
- The dimethyl-[5]helicene represents a highly stable chiral scaffold for advanced applications.
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