A cycloaddition approach to tricyclic taxoid skeletons

Article abstract of DOI:10.1139/v95-278

A cycloaddition approach to the functionalized tricyclo[9.3.1.0^3,8]pentadecene skeleton contained in Taxol is described. The cyclohexenone 13 was converted as illustrated to the nitrile-aldehyde 24 to which the diene and acetylenic side chains were attached by sequential nucleophilic additions. Removal of the trimethylsilyl protecting group and Dess-Martin oxidation afforded the triene 35. Microwave-assisted thermal cyclization stereoselectively generated the tricyclic ketone 36 whose structure was further established by conversion to the aromatic system 37 upon treatment with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). An epoxidation sequence was developed to introduce the epimeric C13 alcohol 47 as required for this cycloaddition strategy. Alternatively, an allylic oxidation (CrO₃, 3,5-dimethylpyrazole) afforded the C13 ketone 49.