Asymmetric biomimetic oxidations of phenols: the mechanism of the diastereo- and enantioselective synthesis of dehydrodiconiferyl ferulate (DDF) and dehydrodiconiferyl alcohol (DDA)

Stereoselective bimolecular radical coupling of enantiopure phenylpropenoidic phenols are described, starting from enantiopure amidic derivatives of ferulic acid. The latter were prepared from ferulic acid by reaction with (S)-alanine or Oppolzer camphor sultam. The oxidation step was performed both enzymatically (HRP/H2O2) and chemically (Ag2O). The observed enantioselectivity in the oxidation step encompasses the range 65–84% and is consistent with the conformational analysis of the quinone methide intermediates at the PM3 level.