REDUCTIVE CYCLIZATION OF (3-OXOALKYL)-9,10-ANTHRAQUINONES AND (4-OXOALKYL)-9,10-ANTHRAQUINONES TO THE CYCLOPENTA[A]ANTHRAQUINONE AND NAPHTHACENE-5,12-DIONE SYSTEMS

Reductive cyclization of the 1-hydroxy-3-(3-oxoalkyl)-9,10-anthraquino nes 2, 9 and 10 yields the angularly condensed cyclopenta[a]anthraquin ones 3, 21 and 22a under neutral conditions (DMF/Na2S2O4). By contrast , the linear cyclopenta[b]anthraquinone 23 is isolated from 10 applyin g the usual alkaline Marschalk conditions (aqueous methanol, NaOH, Na2 S2O4). The linearly condensed 5,12-naphthacenequinones 24-28 of differ ent degree of saturation are obtained in good combined yield from the corresponding 1-hydroxy-3-(4-oxoalkyl)-9,10-anthraquinones 19 and 20 u nder the conditions of the Marschalk reaction.