Asymmetric synthesis of optically active anthracyclinone intermediate and 4-demethoxyanthracyclinones by the use of a novel chiral reducing agent.

Abstract

Asymmetric reduction of 2-acetyl-5, 8-dimethoxy-3, 4-dihydronaphthalene (1) with a novel modified hydride, originally prepared by partial decomposition of lithium aluminum hydride with (1R, 2S)-(-)-N-methylephedrine (1.0 eq) and N-ethylaniline (2.0 eq), was found to proceed highly stereoselectively, giving (S)-(-)-2-1'-hydroxyethyl-5, 8-dimethoxy-3, 4-dihydronaphthalene ((S)-(-)-2) in 100% chemical and 92% optical yields. Direct recrystallzation of (S)-(-)-2, 92% e.e., afforded optically pure (S)-(-)-2 in 87% yield based on 1. Optically pure (S)-(-)-2 was converted to (R)-(-)-2-acetyl-5, 8-dimethoxy-1, 2, 3, 4-tetrahydro-2-naphthol ((R)-(-)-3), 100% e.e., a versatile key intermediate for optically active anthracyclinone synthesis, in a good overall yield according to the reaction scheme established in the preceding paper. Synthesis of optically pure (+)-4-demethoxydaunomycinone ((+)-4d) and (+)-4-demethoxyadramycinone ((+)-4c) was accomplished by using optically pure (R)-(-)-3 as a starting material and by following the reported synthetic scheme with slight modifications.