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Electrochemical Synthesis of Dimerizing and Nondimerizing Orthoquinone Monoketals

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posted on 10.12.2004, 00:00 by Denis Deffieux, Isabelle Fabre, Alexander Titz, Jean-Michel Léger, Stéphane Quideau
Anodic oxidation of appropriately substituted 2-methoxyphenols or α-(2-methoxyphenoxy)-2-methylpropionic acids in the presence of methanol furnishes stable orthoquinone monoketals, and thus constitutes a valuable alternative to the use of chemical oxidants that are often based on toxic metallic species. The propionic acid derivatives are initially converted into O-spirolactonic quinone bisketals that are then selectively hydrolyzed into the desired monoketal compounds. In the absence of blocking substituents, orthoquinone monoketals spontaneously undergo Diels−Alder dimerizations into tricyclododecadienedienones with extraordinary site selectivity, regioselectivity, and stereoselectivity. Suggestions are made to open up a new track for a long awaited rationalization of these controls on the basis of the intramolecular [2 + 2] reactivity of these orthoquinone monoketal-derived cyclodimers.