Analysis of the tautomeric structures of auronols by 13C n.m.r. and comparison with the isomeric flavonols

Abstract

The ¹³C n.m.r. spectra of a series of auronols and flavonols have been analysed in order to determine the tautomeric structures of the auronols and to distinguish between the two series. By using a specifically ¹³C labelled auronol sample, together with coupling constants, changes on additin of D₂O, and solvent-shift data, it has been shownthat auronol and 6-substituted auronols exist in solution as the 2-benzoyl-3-hydroxybenzofurans whereas 4,6 dihydroxyauronol exists as a mixture of the E- and Z-7′-hydroxyaurones.