AN INTRAMOLECULAR DIELS-ALDER APPROACH TO TRICYCLIC TAXOID SKELETONS

A direct, intramolecular cycloaddition route to functionalized tricyclic taxanes is described. This will facilitate the preparation of potentially useful analogues and ultimately the total synthesis of taxol. The cyclohexenone 2 is converted as illustrated to the trimethylcyclohexene 9 to which the diene and acetylenic side chains are attached by sequential nucleophilic additions. Removal of the trimethylsilyl protecting group and Dess-Martin oxidation afforded the triene 13. Microwave assisted thermal cyclization generated the tricyclic ketone 14 stereoselectively whose structure was further established by conversion to the aromatic system 15 upon treatment with DDQ.