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J Org Chem. 2002 Jun 28;67(13):4458-65.

Electrochemically-induced spirolactonization of alpha-(methoxyphenoxy)alkanoic acids into quinone ketals.

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Laboratoire de Chimie des Substances Végétales, Centre de Recherche en Chimie Moléculaire, Université Bordeaux 1, 351 cours de la Libération, 33405 Talence Cedex, France.


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.


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