Synthesis of unsymmetrical 3,3′-biquinazoline-2,2′-diones by condensation of 3-aminoquinazolinones with benzoxazinones; fortuitous discovery, and further syntheses of 4-H-3-oxo-1,9a,10-triazaanthracen-9-ones

Condensation of 2-alkyl- or 2-aryl-3-aminoquinazolin-4-ones with benz[1,3]oxazin-4-ones gives the unsymmetrical 2,2′disubstituted 3,3′biquinazoline-4,4′-diones. The reaction is tolerant to a range of heteroatom and unsaturated functionality in the quinazolinone 2-position. However, treatment of 3-amino-2-hydroxymethyl-3H-quinazolin-4-ones with benz[1,3]oxazinone at high temperatures gave 4H-3-oxo-1,9a,10-triazaanthracen-9-ones, an unreported fused heterocyclic system, a more direct synthesis of which, replacing benzoxazinones with orthoesters is presented.