Oxidative NHC Catalysis: An Unconventional Tool for Macrocyclic Oligoesters Synthesis

Area of Science:

• Organic Chemistry
• Polymer Chemistry
• Sustainable Chemistry

Background:

• Traditional synthesis of macrocyclic oligoesters (MCOs) often involves toxic reagents like diacyl chlorides.
• Developing greener, more atom-economical synthetic routes is crucial for sustainable chemical manufacturing.

Purpose of the Study:

• To present a novel, metal-free N-heterocyclic carbene (NHC) catalyzed protocol for synthesizing MCOs.
• To establish an atom-economical and environmentally friendly alternative to conventional MCO synthesis.

Main Methods:

• Utilized N-heterocyclic carbene (NHC) catalysis under dilute oxidative conditions for polycondensation of dialdehydes and diols.
• Employed the green solvent methyltetrahydrofuran (Me-THF) and a recyclable quinone oxidant.
• Investigated the synthesis of MCOs using both fossil-based and bio-based monomers, including 2,5-diformylfuran (DFF) and 2,5-bis(hydroxymethyl)furan (BHMF).

Main Results:

• Achieved straightforward access to MCOs, avoiding toxic diacyl chlorides.
• Synthesized a range of novel and known MCOs with yields between 51-86%, comparable to traditional methods.
• Demonstrated the versatility of the protocol with various monomers and confirmed structures via NMR and MALDI-TOF MS.

Conclusions:

• The NHC-catalyzed method provides an efficient, sustainable, and metal-free pathway to MCOs.
• The synthesized macrocycles are valuable building blocks, as evidenced by their successful application in entropically-driven ring-opening polymerization (ED-ROP).
• Optimized the organocatalyzed synthesis of poly(2,5-furan-dimethylene 2,5 furandicarboxylate) (PBHMF) via ED-ROP, achieving high molecular weight and yield.