1,3-Dimethylbarbituric acid (1,3-Dimethyl-2,4,6(1H,3H,5H)-pyrimidinetrione) is an active methylene compound. It undergoes hollow Pd6 water-soluble cage, [{(tmen)Pd}6(timb)4](NO3)12 (tmen= N,N,N′,N′-tetramethylethylenediamine, timb=1,3,5-tris(1-imidazolyl)benzene)-catalyzed Knoevenagel condensation reaction with pyrene-1-carboxaldehyde. It undergoes self-sorted Pd7 molecular boat having an internal nanocavity (catalyst)-assisted Knoevenagel condensation reaction with various aromatic aldehydes. It has been synthesized by reacting 1,3-dimethylurea, malonic acid and acetic anhydride in acetic acid. It is widely used for the synthesis of various synthetic intermediates and heterocyclic compounds.