Cycloaddition chemistry of dichloronaphthoquinones has led to regioselective syntheses of all regioisomeric α-O- methyl derivatives of morindone (2) and nataloe-emodin (4), including the natural anthraquinone ethers (1) and (3).
The 2,3-dioxy-1,4-anthraquinones (6) and (7) have been synthesized from the 9,10-anthraquinone (19), through the anthrone (18). Quinones (6) and (7) respectively possess substituents appropriate for three of the four rings of tetracenomycins C (2) and X (3) but they did not show dienophilic properties towards the reactive diene (5). Interaction with the diene was complicated by transsilylation, as was also observed for the model quinone (25).