Modified Kappa‐Carrageenan as a Heterogeneous Green Catalyst for the Synthesis of Nitrogen and Sulfur‐Containing Indenone‐Fused Heterocyclic Compounds

The three component reaction of aromatic aldehydes and 1,3‐indandione in the presence of 4‐amino‐6‐hydroxy‐2‐mercaptopyrimidine is catalyzed by active kappa‐carrageenan under mild conditions to afford the desired products in clean reaction profiles. The kappa carrageenan sources are bioavailable and are extracted from Chondrus crispus , a red seaweed. The catalyst could be prepared by mixing of kappa‐carrageenan in a mechanical mortar for 5 min in a simple step. Good yields with superior atom economy, green and recyclable catalyst with natural source, and simple work‐up are the main advantages of the method for the synthesis of dihydropyridopyrimidines.