STUDIES ON QUINONES .28. NOVEL REARRANGEMENTS OF DIELS-ALDER ADDUCTS OF NAPHTHO-DIQUINONES AND ANTHRADIQUINONES

The Diels-Alder adducts 7a,b by acidic hydrolysis afford the alcohols 8a,b, which in the presence of silica gel, rearrange into the quinizarin derivative 10a and minor amounts of the naphthofuran 11. The rearrangement of 8a,b with silica gel in the presence of ethanol affords the naphthofuran type products 12 and 15. The thermal rearrangement of alcohols 8a,b by heating in benzene solution affords a mixture of the rearranged products 10a,b and the spirocompound 18. Under similar thermal conditions, the alcohol 3 produced the leuconaphthazarin derivative 19 and the spirocompound 20.