Synthetic Anthracyclinones, XXXI. Total Synthesis of Racemic ϵe‐Rhodomycinones via Keto‐Ester Cyclization

The keto esters 15 – 17b were prepared by regioselective alkylation of the anthraquinone acetals 12 – 14 followed by cleavage of the acetals and methyl ethers and esterification. The tetracyclic trans‐β‐hydroxy esters 25 – 27b were formed predominantly upon treatment of 15 – 17b with Triton B in pyridine, whereas lithium amides in THF gave only the cis‐hydroxy esters 28 and 29a. Stereoselective hydroxylation of 25 – 27b afforded the rhodomycinones 38 – 40a and 6 of natural configuration (cis‐2,4‐diols), while that of 28 – 30b gave the not naturally occurring trans‐2,4‐diols 41 – 43b.