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  • Title: A delicate balance of energetics. Subtleties associated with alpha-ketol-based bridge migration to afford 9-keto-10beta-p-methoxybenzyloxytaxanes.
    Author: Paquette LA, Lo HY, Hofferberth JE, Gallucci JC.
    Journal: J Org Chem; 2003 Mar 21; 68(6):2276-81. PubMed ID: 12636391.
    Abstract:
    The feasibility of the title reaction has been pursued for the purpose of advancing a concise total synthesis of Taxol. Of the two closely related series examined, the first featured an exo-methylene group at C4. The second consisted of an alpha-epoxide at that site. Strikingly, the olefinic construct proved inert to attempted alpha-ketol rearrangement. In contrast, the oxiranyl derivative isomerized smoothly. The reaction sequence associated with arrival at taxane 18 is short (15 steps from a D-camphor derivative) and notably efficient. The thermodynamic issues that are raised by this investigation have been clarified by an assessment of molecular mechanics-derived (MM3) steric energy calculations.
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