PTSA-Catalyzed Cyclization of 6-Aminouracils with Diimines: Efficient Synthesis of Functionalized Tetrahydropyrimido[4,5-d]pyrimidine-2,4-diones

A new and efficient method has been developed for the synthesis of 5,7-diaryl-5,6,7,8-tetrahydropyrimido[4,5-d]pyrimidine-2,4-dione derivatives by cyclization of 6-aminouracils with N,N '-bis(arylmethylidene)arylmethanes (diimines). The products were formed in good yields and with very good anti-diastereoselectivity. The best yields were obtained when p-toluenesulfonic acid (PTSA) was used as the catalyst. The solvent also played an important role in the optimization. An amino-substituted 6-aminouracil and a corresponding sulfur analog could be successfully employed. In addition, various diimines, electron rich and neutral, could be successfully employed. The products are of relevance as analogs of biologically active drugs and natural products.