Oxidation of 3β,28-Diacetoxy-18-lupen-21-one with Peroxy Acids: A Way to Des-E-lupane Derivatives
Oxidation of 3β,28-diacetoxy-18-lupen-21-one ( I ) and its 18β, 19β-epoxy derivative III with peracetic acid, catalyzed with strong acids, proceeds with cleavage of the bond between C-19 and C-21 under formation of E-seco derivatives with hydroxyl and isobutyryl groups on C-18 (spiro lactones V - VII and acid VIII ). Oxidative removal of the isobutyryl fragment in spiro lactone VI by treatment with lead tetraacetate leads to the tetranor derivative - keto lactone XI which in an alkaline medium loses formaldehyde from C-17 to give des-E acid XVI .