Deffieux Denis, Fabre Isabelle, Courseille Christian, Quideau Stéphane
Laboratoire de Chimie des Substances Végétales, Centre de Recherche en Chimie Moléculaire, Université Bordeaux 1, 351 cours de la Libération, 33405 Talence Cedex, France.
J Org Chem. 2002 Jun 28;67(13):4458-65. doi: 10.1021/jo020023r.
Anodic oxidation of two series of alpha-(2)- and alpha-(4-methoxyphenoxy)alkanoic acids were studied both at the analytical and preparative scales in order to delineate mechanistic aspects of electrochemically induced spirolactonization and to develop synthetically useful orthoquinone bis- and monoketals. Although alpha-monomethylated carboxylic acids and acetic acid derivatives do not undergo any spiroannulation, alpha-dimethylated carboxylic acids furnished spirolactones in high yields. A gem-dimethyl effect is invoked to explain these differences in cyclization capacity. Electrooxidation conditions can be selected to furnish either quinone spirolactone bis- or monoketals. Chemoselective monohydrolysis of bisketals can also be accomplished in a stepwise fashion to furnish the corresponding spirolactone monoketals, but the ortho compound unfortunately dimerized in situ via a Diels-Alder process. An ECEC pathway is proposed to rationalize the observed spirolactonizations on the basis of cyclic voltammetry analyses.
为了阐明电化学诱导的螺内酯化反应的机理，并开发具有合成价值的邻醌双缩酮和单缩酮，对两个系列的α-(2)-和α-(4-甲氧基苯氧基)链烷酸进行了分析规模和制备规模的阳极氧化研究。尽管α-单甲基化羧酸和乙酸衍生物不发生任何螺环化反应，但α-二甲基化羧酸能以高产率生成螺内酯。引入偕二甲基效应来解释这些环化能力的差异。可以选择电氧化条件来制备醌螺内酯双缩酮或单缩酮。双缩酮的化学选择性单水解也可以逐步完成，以得到相应的螺内酯单缩酮，但不幸的是，邻位化合物通过狄尔斯-阿尔德反应在原位二聚。基于循环伏安分析，提出了一个ECEC途径来解释观察到的螺内酯化反应。
