An alternative, practical, and ecological protocol for synthesis of arylidene analogues of Meldrum's acid as useful intermediates

This paper presents an ecological protocol for Knoevenagel condensation using a catalytic amount of 4,4'-trimethylenedipiperidine as a versatile, efficient, safe, commercially available, inexpensive, and recyclable organocatalyst by a ball-milling process at room temperature. The scope of the present protocol was explored and demonstrated for Knoevenagel condensation of the active methylene, such as Meldrum's acid with various aryl and heteroaryl aldehydes. The developed protocol provides a good to excellent conversion of various aldehydes to respective Knoevenagel products in an environmentally friendly process. Furthermore, this efficient process displays a combination of the synthetic virtues of conventional Knoevenagel condensation with ecological benefits and the convenience of a facile mechanochemistry procedure.