10.1002/ejoc.200900216
The research presents a novel and efficient method for synthesizing pyrimido[5,4-d]pyrimidine N-oxides, which are of significant interest in drug development due to their structural similarity to purines and their potential biological activities. The study explores the reaction of benzylhydroxylamine with 6-cyanopurines to form 7-benzyloxy-8-imino-7,8-dihydropyrimido[5,4-d]pyrimidines, which upon treatment with hydrochloric acid, yield the desired N-oxides. The study concludes that the solubility of the hydrochloride of the intermediate pyrimido-pyrimidines in the reaction solvent plays a crucial role in determining the final product, with soluble hydrochlorides leading to the rearranged product and insoluble ones yielding the N-oxides. This work provides a mild and selective approach to synthesizing these heterocyclic compounds, which could have implications for the development of new pharmaceutical agents.