Synthesis of new heterocyclic phenols: 9‐Hydroxypyrido[1,2‐ a ]pyrimidin‐4‐one and Derivatives

9‐Hydroxypyrido[1,2‐ a ]pyrimidin‐4‐one ( 5 ) was prepared by condensation of 2‐amino‐3‐hydroxypyridine with isopropylidene aminomethylenemalonate. The reaction first led to an enaminoester intermediate which underwent cyclization by heating at 250° affording the new heterocyclic phenol 5 . A similar condensation performed on 2‐amino‐3‐benzyloxypyridine yielded the corresponding benzylic ether which can be easily debenzylated to 5 by hydrogenolysis. Furthermore 2‐amino‐3‐benzyloxypyridine condensed with diethyl ethoxymethylenemalonate gave 9‐benzyloxy‐3‐ethoxycarbonylpyrido[1,2‐ a ]pyrimidin‐4‐one which was also debenzylated to the corresponding free phenol.