Synthesis and properties of 7‐hydroxy‐8‐phenylxanthine and its derivatives. Disproportionation to derivatives of 8‐phenylxanthine and 6‐amino‐5‐nitrosouracil

8‐Phenyl, 8‐(p‐methoxyphenyl) and 8‐(p‐chlorophenyl)‐7‐hydroxyxanthine were synthesized by ring closure of 6‐amino‐5‐nitrosouracil with benzaldehyde, p‐methoxybenzaldehyde and p‐chlorobenzaldehyde, respectively. The disproportionation of these products to the corresponding 8‐phenylxanthines and 6‐amino‐5‐nitrosouracil was studied. The dependence of the rate of the reaction on the various substituents was studied. The disproportionation reaction is inhibited by the polarophilic ethyl acetylenedicarboxylate and enhanced by phosphate.