1,3-Dimethylbarbituric acid is used as a catalyst in the Knoevenagel condensation of a series of aromatic aldehydes. It is also used in the synthesis of 5-aryl-6-(alkyl- or aryl-amino)-1,3-dimethylfuro [2,3-d]pyrimidine derivatives and enantioselective synthesis of isochromene pyrimidinedione derivatives.