A chiral "Siamese-Twin" calix[4]pyrrole tetramer

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Macrocyclic Chemistry

Background:

• Calix[4]pyrroles are versatile macrocyclic platforms with applications in host-guest chemistry.
• Template-directed synthesis is a powerful strategy for constructing complex macrocyclic architectures.
• Oligomacrocycle synthesis often faces challenges with selectivity and yield.

Purpose of the Study:

• To investigate the template effect of bipyridyl N-oxides in the synthesis of calix[4]pyrrole dimers.
• To explore the formation of macrocyclic structures using Hay coupling reactions.
• To characterize novel calix[4]pyrrole-based supramolecular assemblies.

Main Methods:

• Attempted template-directed synthesis of calix[4]pyrrole dimer 4.
• Utilized Hay coupling reaction conditions with tetraalkynyl calix[4]pyrrole 5.
• Employed two bipyridyl N-oxides of different lengths (3 and 6) as templates.

Main Results:

• Short bis-N-oxide 3 resulted in insoluble oligomerization and polycondensation products.
• Long bis-N-oxide 6 did not yield the target dimer 4.
• Isolated a partially reacted calix[4]pyrrole dimer encapsulating 6.
• Obtained an unprecedented calix[4]pyrrole tetramer encapsulating two molecules of 6 in low yield.

Conclusions:

• Bipyridyl N-oxide length significantly influences the outcome of calix[4]pyrrole macrocyclization.
• The study revealed a novel calix[4]pyrrole tetramer with a chiral helical-like conformation.
• This work expands the structural diversity of calix[4]pyrrole-based supramolecular architectures.