Benzologs of allopurinol: Synthesis of pyrazolo [4,3-g] and [3,4-f] quinazolinones

Convenient syntheses of pyrazolo [4,3-g]quinazolin-5 (6H) -one (3), its xanthine oxidase metabolite 4 and the [3,4-f] analog 5 have been developed, involving anellation of the pyrimidine ring onto aminoindazolcarboxylic acids 9 and 18, or attachment of the pyrazol portion onto quinazolinone 22 via intramolecular azo coupling.