Reductive Cyclization of (3-) and (4-Oxoalkyl)-9,10-anthraquinones to the cyclopenta[a]anthraquinone and naphthacene-5,12-dione systems

Abstract

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