STRUCTURE OF DIMERIC COMPOUNDS OBTAINED FROM 22-DIOXO-18-ALPHA,19-BETA-H-URSAN-28,20-BETA-OLIDE

The triterpenoid alpha-diketone with oxabicyclo[2.2.2]octane system in the ring E -21,22-dioxo-18alpha,19betaH-ursan-28,20beta-olide (I)) gi ves isopropylidenedioxy derivative II and dimeric compounds V and IX w hen submitted to chromatography on silica gel in the presence of aceto ne. Compounds V and IX were reduced with hydride to hydroxy derivative s VI, X, and XI; on reaction with diazomethane they gave dimeric compo unds wilh a spiroepoxide group at the position 21 (compound VII) or 22 (compound XII) which reacted further with diazomethane to give monome ric spiroepoxides VIII, XIII, and XIV. The structure of the compounds obtained was derived from their H-1 and C-13 NMR, IR, and FAB mass spe ctra.