From the comparison of the CD curves of (+)-hesperetin (IV) and (-)-hesperetin (V) of known steric configuration with those of protofarrerol (I), farrerol (II), and dihydroprotofarrerol (III), and based on the general rule regarding steric configuration of aryl ketones by CD curves, the steric configuration of the C-2 position in I, II, and III was clarified to be in S-configuration. It was further presumed that the C-1' position in I has the R-configuration from the examination of its CD curve, based on the hypothesis that there is an additivity in the two conjugate systems of 4-chromanone and cyclohexenone systems of I.
