Electrolytic Decarboxylation Reactions. II. Syntheses of Methyl Dihydrojasmonate and Methyl dl-Jasmonate from 3-Methoxycarbonyl-2-carboxynorbornane via Anodic Acetoxylation

Methyl dihydrojasmonate (1a) and methyl dl-jasmonate (1b) were prepared from 3-methoxycarbonyl-2-carboxynorbornane (2a) via anodic acetoxylation. Electrolysis of 2a in a mixed solvent of AcOH-t-BuOH-Et₃N gave a desired key intermediate, exo-2-acetoxy-anti-7-methoxycarbonylnorbornane (3), in 56% yield (GLC peak area) together with several minor products, 4 (12%), 5 (7%), 6 (11%), and 7 (4%). Hydrolysis of 3 followed by oxidation with chromic acid afforded 7-methoxycarbonyl-2-norbornanone (9) in good yield. The Baeyer-Villiger oxidation of 9 and subsequent hydrolysis and oxidation gave 2-methoxycarbonyl-3-methoxycarbonylmethylcyclopentanone (12) in 54% yield. Alkylation of 12 with pentyl and 2-pentynyl bromide and following cis hydrogenation and demethoxycarbonylation afforded 1a and 1b, efficiently.