Syntheses of the aphid pigment derivatives quinone A, quinone A′, and deoxyquinone A as racemates

Abstract

3-Acetyl-5-methoxy-1,7-bisisopropoxy-4-naphthol (11) was converted in a number of high yielding transformations into the title quinones. Key steps were the stereospecific base-induced cyclisation in almost quantitative yield of 2-allyl-4,7-bisbenzyloxy-3-(1-hydroxyethyl)-1,5-dimethoxynaphthalene (18) into 7,10-bisbenzyloxy-3,4-dihydro-5,9-dimethoxy-trans-dimethyl-1H-naphtho[2,3-c]pyran (20) followed by the oxygenation of (20) to afford its two C-4 hydroxy epimers (23) and (26) in high combined yield, by potassium t-butoxide in dimethyl sulphoxide in the presence of oxygen. The efficient conversion of the major pseudoequatorial hydroxy compound (23) into the minor pseudoaxial hydroxy epimer (26)via the corresponding pseudoaxial chloro derivative was useful in providing increased quantities of precursors to quinone A′.