Brønsted Acid Catalyzed Selective Cyclization Reaction: An Efficient and Facile Synthesis of Polysubstituted Imidazole and Pyrrole Derivatives

Abstract

An efficient and facile synthesis of 3-(5-aryl-1,3-dimethyl-2-oxo-2,3-dihydro-1H-imidazol-4-yl)indolin-2-one and 3-(2,5-diaryl-3-oxo-1,2,3,6-tetrahydropyrrolo[2,3-c]pyrazol-4-yl)indolin-2-one derivatives is reported from the selective cyclization reaction of 3-(2-aryl-2-oxoethylidene)indolin-2-one and 1,3-dimethylurea or 5-amino-2-phenyl-2,4-dihydro-3H-pyrazol-3-one under Bronsted acid conditions. Although there are two carbonyl groups in the substrate, the carbonyl group out of isatin is specially chosen for the cyclization reaction to give the target products. The reported products are new five-membered heterocyclic compounds and the results also show that p-toluenesulfonic acid monohydrate (PTSA·H2O) is an effective catalyst for this synthesis. Therefore, the advantages of this approach are excellent yields, short reaction times, operational simplicity, and good regioselectivity.