A New Synthesis of Pteridines

A new synthesis of pteridines possessing a (substituted) (Z)‐3‐hydroxyprop‐1‐enyl group at C(6) is based on the acylation of 4‐amino‐5‐nitrosopyrimidines with dienoic acid chlorides, followed by a high‐yielding intramolecular hetero‐Diels–Alder cycloaddition and cleavage of the N? O bond leading to 4 . Thermolysis of the resulting pteridines 4 possessing a benzyloxy group at C(4) led to the products 5 , resulting from isomerisation of the 3‐hydroxyprop‐1‐enyl to an 3‐oxopropyl side chain, while the analogous pteridine 8 possessing an NH₂ group at C(4) remained unaffected.