The article examines the preparation of a C-1 oxygenated taxane a ring via a highly efficient diels-alder strategy utilizing an α-(aroyloxy) enone captodative dienophile.Most of the diene underwent oligomerization side reactions, presumably mediated by adventitious protic acid impurities in the Lewis acid. The major byproduct was found to be the diene dimer. ion transfer to the BF3catalyst, rendering it ineffective. It was for this reason that benzene, a less acidic and poorly coordinating medium, was initially chosen as the reaction solvent. Performing a control experiment in the absence of added diene allowed researchers to establish that the major byproducts in these reactions were the dienophiledienophile hetero-Diels-Alder cycloadduct 9 and its thermal elimination adduct. © 1997 American Chemical Society.
