Indirect electrooxidation of alkynes 1 using ruthenium tetroxide as a mediator, leading to 1,2-diones 2 in 72-87%, is described. The electrolysis is carried out in the presence of a catalytic amount of ruthenium dioxide dihydrate in a two phase system of saturated aqueous sodium chloride and carbon tetrachloride. The overoxidation of 1,2-diones to the corresponding carboxylic acid, an unavoidable drawback generally encountered in the metal oxidation of acetylenes, is suppressed greatly by maintaining the pH of the aqueous phase at 4 and conducting the reaction at 0-5°C. The synthetic utility of this electrochemical oxidation is exemplified by the preparation of 2i (82%), a key intermediate for the synthesis of furaneol 4, from the commercially available 1i.
使用
四氧化钌作为介质,对
炔烃1进行间接电氧化,以72-87%的产率得到1,2-二酮2。电解在含有催化量
二氧化钌二水合物的
水和
四氯化碳两相体系中进行,使用饱和
氯化钠水溶液。通过将
水相的pH维持在4,并在0-5°C下进行反应,可以大大抑制1,2-二酮过氧化成相应的
羧酸,这是通常在
金属氧化
炔烃中遇到的一个不可避免的缺点。这种方法的合成实用性通过从市售的1i制备关键中间体2i(产率82%)来证明,2i是合成furaneol 4的重要中间体。