Asymmetric Synthesis of Anthracyclinones : Synthesis of a New Chiral AB-Synthon, (5R, 6R)-6-Ethyl-5, 6-dihydroxy-5, 6, 7, 8-tetrahydro-1, 4-naphthoquinone, and Its Application for a Novel Regioselective Synthesis of (-)-γ-Rhodomycinone

Abstract

A new chiral AB-synthon, (5R, 6R)-6-ethyl-5, 6-dihydroxy-5, 6, 7, 8-tetrahydro-1, 4-naphthoquinone (4), for the synthesis of optically active rhodomycinones was prepared stereoselectively from a (-)-α-hydroxy ketone (6). The coupling reactions of 4 with homophthalic anhydride derivatives (9, 12) proceeded in a regioselective manner to give the tetracyclic compounds 10 and 13, respectively. Compound 10 was converted to (-)-γ-rhodomycinone (3) in a two-step sequence. The optical purity (100% ee) of 3 was unambiguously determined by high performance liquid chromatography analysis using a chiral column.