THE CHEMISTRY OF TAXANES - REACTION OF TAXOL AND BACCATIN DERIVATIVES WITH LEWIS-ACIDS IN APROTIC AND PROTIC MEDIA

Several Lewis acids were shown to cleanly open the oxetane ring of taxol and baccatin derivatives. The reaction is shown to proceed via anchimeric assistance by the C-4 acetate group. Several minor products, including a novel derivative possessing a bridged C-ring, were also isolated. A mechanistic rationale is provided for all compounds formed. When taxol derivatives were treated with Lewis acids in methanol, ester cleavage reactions were observed. We provide conditions that are selective for C-10 acetate cleavage and for C-13 side-chain methanolysis.