An Overview of Recent Advances in Biological and Pharmaceutical Developments of Fluoro-containing Drugs

Organocatalytic Synthesis of (Hetero)arylidene Malononitriles Using a More Sustainable, Greener, and Scalable Strategy

AIM AND OBJECTIVE

The establishment of a green and sustainable Knoevenagel condensation reaction in organic chemistry is still crucial. This work aimed to provide a newly developed metal-free and halogen-free catalytic methodology for the synthesis of CS and (hetero-) arylidene malononitriles in the laboratory and industrial scale. The Knoevenagel condensation reaction of various carbonyl groups with malononitrile was investigated in ethanol, an ecofriendly medium, in the presence of seven nitrogen-based organocatalysts.

MATERIALS AND METHODS

A comparative study was conducted using two as-obtained and four commercially available nitrogen-based organocatalysts in Knoevenagel condensation reactions. The synthesis of CS gas (2-chlorobenzylidene malononitrile) using a closed catalytic system was optimized based on their efficiency and greener approach.

RESULTS

The conversion of 100% and excellent yields were obtained in a short time. The products could be crystallized directly from the reaction mixture. After separating pure products, the residue solution was employed directly in the next run without any concentration, activation, purification, or separation. Furthermore, the synthesis of 2-chlorobenzylidenemahmonitrile (CS) was carried out on a large scale using imidazole as a selected nitrogen-based catalyst, afforded crystalline products with 95 ± 2% yield in five consecutive runs.

CONCLUSION

Energy efficiency, cost saving, greener conditions, using only 5 mol% of organocatalyst, high recyclability of catalyst, prevention of waste, recycling extractant by a rotary evaporator for non-crystallized products, demonstrated the potential commercial production of CS using imidazole in ethanol as an efficient and highly recyclable catalytic system.

Halogen bonding organocatalysis enhanced through intramolecular hydrogen bonds

Recent results indicate a halogen bond donor is strengthened through direct interaction with a hydrogen bond to the electron-rich belt of the halogen. Here, this Hydrogen Bond enhanced Halogen Bond (HBeXB) plays a clear role in a catalyst. Our HBeXB catalyst improves product conversion in a halide abstraction reaction over a traditional halogen bonding derivative.