Room temperature catalyst-free Knoevenagel condensation: facile access to isatinylidenerhodanines

A catalyst-free Knoevenagel type synthesis of isatinylidenerhodanines is reported starting from substituted isatins and rhodanines. The reaction proceeds spontaneously at room temperature in dimethyl sulfoxide (DMSO), employing a unique macrocyclic intermediate formed through an intramolecular H-bonding. Various substituted isatinylidenerhodanines could be synthesized in good yields.