The reaction of methyl isoferulate with FeCl3 or Ag2O—hypothesis on the biosynthesis of lithospermic acids and related nor and neolignans

Methyl isoferulate reacts with FeCl3 to give (2-6) dimer 3 (6-6) dimer 4 and (6-O-3) dimer 5 in low yields, whereas it reacts with Ag2O leading to (2-O-3) dimer 6 and (6-O-3, 2-O-3) trimer 7. By comparison with literature data, we suggest that the biosynthesis of lithospermic acids and related nor and neolignans that possess a β-2 bond may be due to the cross dimerisation of ferulate radical on isoferulate.