The first synthesis of spirocyclopentyl derivatives of lupane triterpenoids by radical nitrocyclization of C-2-diallyl substituted betulonates

Radical cyclization of the 1,6-hexadiene moiety in 2,2-diallyl substituted methyl or benzyl dihydrobetulonates initiated by Fe(NO3)3·9H2O in the presence of FeCl3 or LiCl gave hitherto unknown spirocyclic compounds in which ring A of the lupane triterpenoid at position C-2 is spiro coupled with a vicinally substituted nitromethyl- and chloromethylcyclopentane. Based on a quantum-chemical assessment of the energy characteristics of this reaction, the most probable configurations of the chiral atoms in the spirocyclopentane ring were determined for the major diastereomers isolated in individual form.