Diterpenoids. XVII. Epimerization at Lactonization of 6β-Hydroxy-enantio-podocarpan (and 8-monoen-) 16-oic Acid (cis-and trans-B/C-ring Juncture) Syntheses of the Corresponding 6α-Hydroxy Series

Previously, it was found that a remarkable epimerization (βC6-O→α) was occurred when 6β-hydroxy acid (II) was lactonized. In order to further examine on the mechanism and the limitation of the epimerization, the corresponding hydrogenated 6β-hydroxy acids (V, XIV and XXX) were chosen as model. One of them (XXX) was completely different, however the other (V and XIV) were epimerized as similar to (II).