Stereospecific oxidation of diacetoxyheterobetulin with ozone and dimethyldioxirane

Stereospecific oxidation of diacetoxyheterobetulin with ozone and dimethyldioxirane led to 3β,28-diacetoxy-18α,19βH-urs-20α,21α-epoxide with yields of 79% and 87%, respectively. Oxidation with ozone was not selective and gave two minor products containing 2lα-hydroxy-20(30)-ene and 21a-hydroxy-20β,28-epoxy-fragments in ring E. The structures of 3β,28-diacetoxy-18α,19βH-urs-20α,21α-epoxide and 3β-diacetoxy-21α-hydroxy-20β,28-epoxy-18α,19βH-ursane were confirmed by X-ray analysis for the first time.