3p- Friedelanol

Sometimes several of these rearrangements occur in one molecule, either simultaneously or in rapid succession. A spectacular example is found in the triterpene series. Friedelin is a triterpenoid ketone found in cork. Reduction gives 3p-friedelanol (47). When this compound is treated with acid, 13(18)-oleanene (48) is formed. In this case seven 1,2 shifts take place. On removal of H2O from position 3 to leave a positive charge, the following shifts occur hydride from 4 to 3 methyl... 

Successive Wagner-Meerwein rearrangements have been utilized in triterpenoid syntheses. A unique and fascinating example of this can be foimd in Corey s synthesis of the triterpenoid oleanene. When 3P-friedelanol (35) is treated with acid, a total of seven 1,2-alkyl and 1,2-hydride migrations occur leading to the formation of 37. The stereospecific shifts are driven by the apparent decrease in steric strain due to the original location of the axial substituents. Intermediate products have been isolated, supporting the assertion that at least some of the steps are not concerted. 

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