Chemistry of quinones. Part 7. Synthesis of anthracyclinone analogues via Diels–Alder reactions of 1,4-anthraquinones

Diels–Alder adducts were formed by reaction of 1,4-anthraquinone with buta-1,3-diene, with 1-acetoxy-, 1-methyl-, 2-methyl-, and 2,3-dimethyl-buta-1,3-diene, and with cyclohexa-1,3-diene. Adducts were also prepared by reaction of 9-chloro-10-hydroxy-1,4-anthraquinone with buta-1,3-diene and with 2-methylbuta-1,3-diene. Some of the linear tetracyclic adducts were transformed to 1,2,3,4-tetrahydro-1,5,12-trihydroxynaphthacene-6,11-quinone (21) and 2-acetyl-1,2,3,4-tetrahydro-2,5,12-trihydroxynaphthacene-6,11-quinone (7). The latter has been converted by other workers into 4-demethoxydaunomycinone (48) and 4-demethoxydaunomycin (8).