VERSATILE SYNTHESIS OF DIHYDROQUINOLINES AND QUINOLINE QUINONES USINGCYCLOBUTENEDIONES - CONSTRUCTION OF THE PYRIDOACRIDINE RING-SYSTEM

1-BOC-2-lithio-1,4-dihydropyridines were condensed with 3,4-disubstitu ted cyclobutenediones to produce 1,2-adducts. Neat thermolysis under o xygen-free conditions produced substituted 1,4-dihydroquinoline hydroq uinones in which the tert-butoxy residue of the BOC group was displace d by a phenolic residue, generating an oxazolone ring that functioned to protect both rings of the dihydroquinoline hydroquinone from untime ly oxidation. Oxidative aromatization with concomitant loss of the oxa zolone ring was achieved using 2 equiv of o-chloranil in acetic acid a nd provided substituted quinoline quinones in good yields. By use of t his strategy, a concise synthesis of the pyridoacridine ring system wa s achieved.