This article discusses the synthesis of pyrido[2,3-d]pyrimidines, which are important heterocycles found in many pharmaceutically active molecules. The traditional methods for synthesizing these compounds are described, as well as the limitations of these methods. The article then presents a new catalytic system using 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)/tert-Butyl Nitrite (TBN)/O2 for the synthesis of pyrido[2,3-d]pyrimidines. The reaction conditions and optimization are discussed, and the results show promising yields. This research provides a new and efficient method for the synthesis of pyrido[2,3-d]pyrimidines with potential bioactivities. The given document presents a table showing the results of control experiments on the reaction of uracils and 1,3-diarylpropenes. The table includes entries for different combinations of reactants and the corresponding products and yields. The experiments indicate that both TBN and O2 promote the reaction. The table provides specific details about the reactants and products, as well as the corresponding yields. This document describes a novel and efficient method for synthesizing pyrido[2,3-d]pyrimidines/thiopyrido[2,3-d]pyrimidines using easily available starting materials. The reaction involves oxidative coupling, intramolecular cyclization, [Extracted from the article]