Macrocyclic diterpenoids from Euphorbia hyberna L. subsp insularis and their reaction with oxyphilic reagents

The aerial parts of Euphorbia hyberna subsp. insularis from Sardinia contain large amounts of macrocyclic diterpenoids of the jatrophane type, while phorboids could not be isolated. Treatment of the major constituent (1a) with various acidic and oxyphilic reagents was investigated, showing the surprising reluctance of the macrocyclic system to undergo transannular reactions. Dehydration, isomerization of the exocyclic double and acyl rearrangement were, however, observed after reduction of the 9-keto group. (C) 2002 Elsevier Science B.V. All rights reserved.