Naphtho[2,3-c]pyran-5,10-quinones. Syntheses of the racemates of quinone A, quinone A′, and deoxyquinone A dimethyl ethers of 7-methoxyeleutherin, and of isoeleutherin

Abstract

Treatment of 3-(1-hydroxyethyl)-1,4,5,7-tetrarmethoxy-2-prop-2-enylnaphthalene (33) with potassium t-butoxide in dimethylformamide under nitrogen for a short time gave a high yield of trans-3,4-dihydro-5,7,9,10-tetramethoxy-1,3-dimethyl-1H-naphtho[2,3-c]pyran (41). This compound, with the same base and solvent, but in air, afforded a mixture comprising its cis-epimer (42), together with the two possible 4-hydroxy derivatives, namely (35) and (38). Silver(II) oxide oxidation of compounds (35), (38), (41), and (42) gave, respectively, the dimethyl ethers of quinone A, quinone A′, and deoxyquinone A, and also 7-methoxyeleutherin.