Pillar[5]arene as a co-factor in templating rotaxane formation

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Macrocyclic Chemistry

Background:

• Enzymes utilize coenzymes for substrate binding in active sites.
• Macrocycles like pillar[5]arene and cucurbit[6]uril can template chemical reactions.
• Cucurbit[6]uril alone does not template certain azide-alkyne cycloadditions.

Purpose of the Study:

• To investigate the cooperative templation effect of pillar[5]arene and cucurbit[6]uril on azide-alkyne cycloadditions.
• To synthesize novel rotaxane structures using this cooperative templation.
• To explore the role of hydrogen bonding between the macrocycles in the templation process.

Main Methods:

• Cooperative templation of bipyridinium dications with varying azidoalkyl chains using pillar[5]arene and cucurbit[6]uril.
• Orthogonal recognition and hydrogen bonding between the macrocycles to direct rotaxane formation.
• Reaction optimization at 55 °C in acetonitrile for rapid and high-yield synthesis.

Main Results:

• Formation of two [4]rotaxanes and one [5]rotaxane in >90% yield within 2 hours.
• Successful trapping of pillar[5]arene conformational isomers on the rotaxane dumbbell components.
• Isolation of a [5]rotaxane containing two pillar[5]arene rings with C5 symmetry.
• Extension of constitutional scope for regiochemistry in 1,3-dipolar cycloadditions.

Conclusions:

• Pillar[5]arene and cucurbit[6]uril exhibit positive cooperativity in templating azide-alkyne cycloadditions.
• This cooperative effect leads to efficient and green synthesis of complex rotaxanes.
• The system demonstrates orthogonal recognition and templation under mild conditions.