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

9-Hydroxypyrido1,2-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-ethoxycarbonylpyrido1,2-a]pyrimidin-4-one which was also debenzylated to the corresponding free phenol.