Solvent-free and green synthesis of fused pyrimidine derivatives catalyzed by pillar[5]arene-based Lewis acid ionic liquid.

This study presents a solvent-free and green approach for the synthesis of novel 7,9-diaryl-6H,7H-chromeno[4,3-d]thiazolo[3,2-a]pyrimidin-6-one (DCTP) derivatives using a newly developed pillar[5] arene-based Lewis acid ionic liquid (P5/Py[CuBr2]Br) as catalyst. This catalytic system efficiently facilitates a one-pot, three-component reaction between 4-aminocoumarin, aromatic aldehydes, and 1-aryl-2-thiocyanatoethan-1-ones under solvent-free conditions. A wide range of DCTP derivatives were obtained in high to excellent yields (70–95%), demonstrating the tolerance of the catalyst for various functional groups. This protocol can also be used for the selective synthesis of mono-DCTP derivatives from dialdehydes. Key advantages of this methodology are excellent catalyst reusability over six runs without significant loss of its activity, high atom economy, low E-factor, and high turnover numbers (TON ~ 52–70), which are aligned with the principles of green chemistry. This work also highlights the significant potential of functionalized pillar[n]arenes in promoting sustainable and efficient multicomponent reactions for constructing complex fine heterocyclic scaffolds.