Synthesis and Functionalization of C6/C7 Substituted Pyrido[3,2‐d]pyrimidines

An efficient synthesis of functionalized pyrido[3,2‐ d ]pyrimidines is reported. Starting from 4‐aminopyrimidine‐3‐carbaldehydes, a Horner‐Wadsworth‐Emmons olefination followed by a photoisomerization/cyclization installed the fused pyridine ring. Using substituted HWE‐reagents various substituents could be introduced in the 7‐position of the pyrido[3,2‐ d ]pyrimidines. Functionalization of the pyridone substructure allowed late variation in the 6‐position. In order to obtain amine‐linked bis‐pyridopyrimidines, 7‐bromo‐pyridopyrimidines were converted with their 7‐amino‐counterpart by Hartwig–Buchwald amination.