The simple and regioseletive oxidation of 6-alkylazulene derivatives with an electron-withdrawing substituent at the 1-position of the azulene ring is described. Oxidation with molecular oxygen proceeds smoothly in the presence of a base such as potassium acetate (KOAc) or tetrabutylammonium hydroxide (Bu4NOH), and appears to proceed via enolization of the azulene derivatives. Oxidation of 6-isopropylazulene derivatives gave tertiary alcohols, which were easily converted to primary alcohols. Oxidation of 6-methylazulene derivatives provided azulene-6-carboxylate derivatives but dimethhyl azulene-1,6-dicarboxylate, which had been obtained by the oxidation of methyl 6-methylazulene-1-carboxylate, was found to be reduced selectively at the 6-position by sodium borohydride (NaBH4). In contrast, demethoxycarbonylation of dimethyl azulene-1,6-di-carboxylate with anhydrous phosphoric acid (100%PA) proceeded selectively at the 1-position to give methyl azulene-6-carboxylate. Those compounds obtained by the oxidation of 6-alkylazulenes are useful key intermediates for further modifications of the side chains at the 6-position of azulenes.
描述了在薁环 1 位具有吸电子取代基的 6-烷基薁衍
生物的简单和区域选择性氧化。分子氧的氧化在
乙酸钾 (KOAc) 或
氢氧化四丁基铵 (Bu4NOH) 等碱存在下顺利进行,并且似乎是通过甘菊环衍
生物的烯醇化进行的。 6-异丙基薁衍
生物的氧化得到叔醇,该叔醇很容易转化为伯醇。 6-甲基薁衍
生物的氧化提供了薁-6-
羧酸酯衍
生物,但通过氧化6-甲基薁-1-
甲酸甲酯而获得的二甲基薁-1,6-二
羧酸酯被发现在6-位被选择性还原。
硼氢化钠(NaBH4)的位置。相比之下,1,6-二
甲酸二甲酯与无
水磷酸(100%PA)在1位选择性地进行脱甲氧基羰基化,得到6-
甲酸甲酯。通过氧化 6-烷基甘菊环得到的那些化合物是进一步修饰甘菊环 6 位侧链的有用的关键中间体。