Calixrotanes: Calixarenes Incorporating Spiro-Linked Cyclopropyl Groups

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Crystal Engineering

Background:

• Macrocyclic compounds like calixarenes are versatile platforms in supramolecular chemistry.
• Introducing rigid structural elements can tune the properties of macrocycles.
• Spirocyclopropyl groups offer unique steric and electronic features.

Purpose of the Study:

• To synthesize novel macrocyclic compounds incorporating spirocyclopropyl linkers.
• To characterize the structure and conformation of these new calixarene derivatives.
• To investigate the impact of spirocyclopropyl groups on macrocyclic rigidity.

Main Methods:

• Synthesis of calixarene derivatives with exocyclic double bonds.
• Reaction with dichlorocarbene to form spirocyclopropyl intermediates.
• Reductive perdechlorination to yield final spirocyclopropyl macrocycles.
• Structural characterization using X-ray crystallography and NMR spectroscopy.

Main Results:

• Successful synthesis and structural characterization of calix[4]- and calix[6]arene derivatives with spirocyclopropyl groups.
• Observed anti-orientation of geminal rings and isoclinal positioning of methylene groups in cyclopropyl rings.
• Calix[6]rotane exhibits a 1,3,5-alternate conformation in both solid state and solution.
• Spirocyclopropyl incorporation significantly enhances the rigidity of the macrocyclic framework.

Conclusions:

• Novel spirocyclopropyl-linked calixarene macrocycles have been developed.
• The spirocyclopropyl units impart significant conformational rigidity.
• These findings open avenues for designing conformationally restricted macrocyclic hosts and materials.