Diastereoselective anodic hetero- and homo-coupling of menthol-, 8-methylmenthol- and 8-phenylmenthol-2-alkylmalonates.
Diastereoselective radical coupling was achieved with chiral auxiliaries. The radicals were generated by anodic decarboxylation of five malonic acid derivatives. These were prepared from benzyl malonates and four menthol auxiliaries. Coelectrolyses with 3,3-dimethylbutanoic acid in methanol at platinum electrodes in an undivided cell afforded hetero-coupling products in 22-69% yield with a diastereoselectivity ranging from 5 to 65% de. Electrolyses without a coacid led to diastereomeric homo-coupling products in 21-50% yield with ratios of diastereomers being 1.17:2.00:0.81 to 7.03:2.00. The stereochemistry of the new stereogenic centers was confirmed by X-ray structure analysis and13C NMR data.
Organisch-Chemisches Institut der Westfälischen Wilhelms- Universität, Corrensstraße 40, D-48149 Münster, Germany.
Matthias C
MC
Letzel
Organisch-Chemisches Institut der Westfälischen Wilhelms- Universität, Corrensstraße 40, D-48149 Münster, Germany.
Hans J
HJ
Schäfer
Organisch-Chemisches Institut der Westfälischen Wilhelms- Universität, Corrensstraße 40, D-48149 Münster, Germany.
Roland
R
Fröhlich
Kolbe electrolysis; anodic decarboxylation; diastereoselectivity; radical hetero-coupling; radical homo-coupling