An efficient catalyst- and base-free, three-component tandem annulation has been developed for the synthesis of pyrido4,3-dpyrimidine-2,4-diones. This strategy employs readily available 5-carbonyl-6-methyluracils, aldehydes, and ammonium iodide under an oxygen atmosphere, affording the target products in good to excellent yields with broad substrate compatibility. The transformation is proposed to proceed via a condensation/cyclization/oxidative dehydrogenation cascade. This method offers notable advantages, such as operational simplicity and environmental benignity, thereby presenting a practical alternative route for the construction of pyrido4,3-dpyrimidine-2,4-diones.
Chen et al. (Mon,) studied this question.