Electrochemical Synthesis of Dimerizing and Nondimerizing Orthoquinone Monoketals

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.