κ-Carrageenan as an efficient, green, bifunctional and reusable catalyst for one-pot synthesis of Hantzsch 1,4-dihydropyridine

Developing chemical processes using more environmentally acceptable catalysts, chemicals and atom efficient procedures have been emerged as subjects of innovation in green chemistry. For instance, the terrible impact of non-biodegradable wastes is still an open challenge in either developed or developing countries. In this regard, great efforts have been performed to use different bio-based feedstocks such as chitosan, chitin, starch, cellulose, gelatin, wool and alginates as biopolymeric support in the transition metal-based heterogeneous catalytic systems. On the other hand, multicomponent reactions have been recognized as a vast improvement for synthetic chemists. Multicomponent reactions are the reactions with three or more substratets, which lead to the production of complex molecules, especially heterocyclic complex products.1-3 Carrageenan is a natural carbohydrate (polysaccharide) obtained from edible red seaweeds. Carrageenans are used in a variety of commercial applications as gelling, thickening, and stabilising agents, especially in food products and sauces. Carrageenans are also used in pharmaceutical, drug delivery, cosmetics, experimental medicine and textile industries.4Kappa-Carrageenan was found to be an efficient, bifunctional, recyclable, economical, environment-friendly and green catalyst for the one-pot multicomponent synthesis of 1,4-dihydropyridines (1,4-DHPs) via the Hantzsch reaction. The mild reaction conditions, short reaction times, good yields and the nontoxic catalyst make this method especially attractive.5, 6