Selective oxidation of oleanane triterpenoids

Abstract

Reagent A (exact composition unknown) was obtained from a mixture of CrO₃, pyridine, and BuⁿOH saturated with water. The reaction of the oleanane triterpenoid glycosides (1), (4), and (5) with reagent A gave 11-oxo-compounds (3) and (6), which indicated that this reagent is useful for the oxidation of an allyl alcohol and an allyl ether. On the other hand, the reaction of oleanane triterpenoids (11), (13), (14), and (15) with reagent A gave 16-oxo-derivatives (9), (16), (17) and (18), while compounds (19) and (22) with this reagent gave 21-oxo-derivatives (24) and (25). Reagent A is also very useful for the selective oxidation of 16- and 21-axial hydroxy-groups.