Several 2,3-dihydro-7H-dibenzo(de,h)quinolin-7-ones and 7H-dibenzo(de,h)quinolin-7-ones were catalytically hydro- genated over PtO2 in acetic acid to afford 7-hydroxyquinoline and quinolone derivatives with reduced benzene rings. A limited number of compounds with the 7H-diben- zo(de,h)quinoline skeleton, known as 1-azabenzan- thrones, were synthesized three decades ago as intermediates for the formation of dyes, 1 and due to their possible photo- and electrochemical properties. 2 About the same time, the synthesis of 7H-dibenzo(de,h)quinolin- 7-one derivatives via N-phenethylphthalimides was re- ported in connection with their possible antiviral activity, 3 and the synthesis of some 2,3-dihydro derivatives by cy- clization of 3-(b-dialkoxyarylethylamino)phthalides was also reported. 4 In the case of the 5-methoxy-2,3-dihydro analogue (2), this compound was obtained in large enough quantities to subject it to some preliminary reduction stud- ies, affording a basic carbinol whose structure, however, was not adequately confirmed. Since the 1980's, a small group of alkaloids possessing the 7H-dibenzo(de,h)quin- oline skeleton and bearing different substitution patterns have been isolated from Menispermum dauricum DC. (Menispermaceae) and designated as oxoisoaporphines. 5 Some of them have exhibited cytotoxic activities against a small panel of cancer cell lines. 6 In the structurally sim- ilar oxoaporphines (7H-dibenzo(de,g)quinolin-7-ones), which might also be called 6-azabenzanthrones, the re- duction of the carbonyl group had been carried out under mild conditions, affording aporphines, 7 but no similar re- sults have been recorded for the oxoisoaporphines. In this connection it is interesting that, unlike the oxoaporphines, the oxoisoaporphines are not accompanied in plants by their reduced (or unoxidized) congeners. Due to the lack of information on the reactivity of these compounds under reductive conditions, we have now studied the catalytic hydrogenation of several 2,3-dihy- drooxoisoaporphines over Adams' catalyst. This method is useful for the preparation of new and unusual oxo- isoaporphine and quinoline derivatives, due to its simp- licity and efficiency. The dihydro- and oxoisoaporphines used in this work and the generated products are summarized in Table 1. In all cases, hydrogenation was carried out for 24 hours at room temperature at pressures between 60-70 psi. 8 Under these conditions, complete or partial reduction of aromatic ring D and of the C-N imine bond of the dihydrooxoisoapor- phines resulted (Scheme 1). However, in the case of the oxoisoaporphines, aromatic rings B and D were reduced (Scheme 2). Thus, the chemoreduction shown by these compounds would seem to depend mainly on the substitu- tion at C-6 and on the degree of unsaturation of the iso- quinoline skeleton. When Pd/C was used as catalyst, the unchanged starting material was recovered. As can be seen in Scheme 1, the 2,3-dihydrooxoisoapor- phines 1 and 2, lacking a hydroxyl group at C-6, are par- tially reduced in ring D without affecting the C=N bond, affording 4 and 5 respectively. Hydrogenation of com- pound 3, with an OH group at C-6, under identical condi- tions, led to complete reduction of ring D and the C=N bond to give 6.