Potassium 2-methyl-5-hydroxy-6, 7-benzochromon-8-y1 sulfate (VIII) and potassium 2-methyl-5-hydroxy-7, 8-benzochromon-6-y1 sulfate (IX) were synthesized from 2-methyl-5, 8-dihydroxy-6, 7-benzochromone (I) and 2-methyl-5, 6-dihydroxy-7, 8-benzochromone (II). Hydroxylation of 2-methyl-5-hydroxy-6, 7-benzochromone (III) and 2-methyl-5-hydroxy-7, 8-benzochromone (IV) gave 2-methyl-4H-naphtho[2, 3-b]pyran-4, 5, 10(5H, 10H)-trione (V) from both, and the mechanisms of the abnormal reaction were investigated. It was found that V is also obtained from IX in the same condition as hydroxylation and that 2-methyl-4H-naphtho[1, 2-b]pyran-4, 5, 6(5H, 6H)-trione (X) underwent ring isomerization to V directly or through a diketone, 2-acetoacetyl-3-hydroxy-1, 4-naphthoquinone (XI), as an intermadiate. Synthesis of I from II and that of 2-methyl-3-acetyl-5, 8-dihydroxy-6, 7-benzochromone (VI) from 2-methyl-3-acethyl-5, 6-dihydroxy-7, 8-benzochromone (VII) was accomplished by the application of a novel reaction together with a new oxidation method using sodium nitrite. VI also underwent ring isomerization to VII. Thus, it was found that acetyl group at 3-position in VI or 2-methyl-3-acetyl-4H-naphtho[1, 2-b]pyran-4, 5, 6(5H, 6H)-trione (XIII) was not eliminated during two kinds of ring isomerization described.
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