An Efficient and Versatile Deep Eutectic Solvent-Mediated Green Method for the Synthesis of Functionalized Coumarins

Area of Science:

• Organic Chemistry
• Green Chemistry
• Synthetic Chemistry

Background:

• Coumarins are vital heterocyclic compounds with diverse applications.
• Traditional coumarin synthesis often involves harsh conditions and toxic reagents.
• Developing sustainable and efficient synthetic methodologies is crucial.

Purpose of the Study:

• To develop a green and efficient synthetic route for functionalized coumarins.
• To explore the use of a deep eutectic solvent (DES) as both solvent and catalyst.
• To demonstrate the scalability and reusability of the proposed method.

Main Methods:

• Utilized the Pechmann condensation reaction.
• Employed a biodegradable, reusable, and inexpensive deep eutectic solvent (DES) composed of choline chloride and l-(+)-tartaric acid (1:2 ratio).
• Optimized reaction conditions for both coumarin and bis-coumarin synthesis at 110 °C and 90 °C, respectively.

Main Results:

• Achieved good-to-excellent yields (60-98%) for diverse functionalized coumarins.
• Synthesized functionalized coumarin (20) in 98% yield within 10 min using phloroglucinol and ethyl acetoacetate.
• Produced bis-coumarins in 81-97% yields within 20-45 min at 90 °C.
• Demonstrated successful large-scale synthesis without significant yield reduction.
• Showcased the reusability of the DES catalyst four times with no substantial loss in product yield.

Conclusions:

• The developed Pechmann condensation using DES is a green, efficient, and scalable method for coumarin and bis-coumarin synthesis.
• The DES acts as a dual-purpose solvent and catalyst, enhancing sustainability.
• This approach offers a cost-effective and environmentally friendly alternative for coumarin production.