One-pot anodic lactonization of Fenchone and Menthone and electrosynthesis of a new magnolione analogue

• Green and good-yield formation of valuable δ-lactones by anodic oxidation.
• Dependence of the type of products on the electrolyte.
• Electrosynthesis of a Magnolione analogue in only one-step.
• Electrolyte dependence in the mechanism pathway of electrogenerated terpenoid cation radicals.

The terpenoid cycloalkanones Fenchone and Menthone have been oxidized at a platinum anode under neutral and alkaline electrolyte conditions. When NaClO4 was used as electrolyte, Fenchone (1a) afforded 1-isopropyl-4-methyl-2-oxa-bicyclo[2.2.1]heptan-3-one, and Menthone (1b) provided the stable lactone 6-isobutyl-4-methyl-tetrahydropyran-2-one, both in good yield. When using Na2CO3 as electrolyte, the oxidation of 1a gave the fragrance-analogue 2,2-dimethyl-3-(2-oxopropyl) cyclopentanone in only one-pot. Mechanism proposals are presented.

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