Experiments Directed Towards the Synthesis of Anthracyclinones. XXXI. Reductive Claisen Rearrangements of Bis(allyloxy)anthraquinones

A reinvestigation of the reductive Claisen rearrangement of the bis(allyloxy)anthraquinones (1) and (2) with sodium dithionite of high quality has afforded new compounds. These include inter alia diastereomeric pairs of doubly rearranged leuco 1,4-dihydroxyanthraquinones in the diketo form [(14) and (16); (15) and (17)], products derived from attack on or rearrangement to a quinone carbonyl group, e.g. (28) and (29), and in the case of (1) a 10-deoxygenated 1,4-anthraquinone (21). Structures have been assigned from two-dimensional n.m.r. experiments.