Allobetulin was converted to 3β-acetoxy-21β-acetyl-20β,28-epoxy-18α,19β-ursane, followed by reduction of the acetyl fragment and acid-catalyzed dehydration product. The structure of the obtained triterpenoid containing a trans-ethylidene substituent on the E ring was determined using two-dimensional 1H–1H COSY, 1H–1H NOESY, 1H–13C HSQC, 1H–13C HMBC correlation techniques.