The Pd(0) based synthesis of two disilyl synthons (Z-1-trimethylsilyl-6-tert-butyldiphenylsilylhex-3-ene-1,5-diyne (18) and Z-1-trimethylsilyl-6-triisopropylsilylhex-3-ene-1,5-diyne (19)) and the selective removal of the trimethylsilyl group (K2CO3, MeOH) to afford 24 and 25 is described. These building blocks are employed in the construction of the taxamycin-12 compound 38 (16,17,18-trimethyl-2-methyloxymethoxy-9-hydroxybicyclo[9.3.1]pentadec-5-ene-3,7-diyne). The final ring closure to the 12-membered ring utilizes an intramolecular Cr–Ni mediated condensation of the iodoalkyne 37 (1,3,3-trimethyl-2-(2-oxoethyl)-4-(Z-1-methyloxymethoxy-7-iodohept-4-ene-2,6-diynyl)cyclohexene). Keyword: cancer, enediynes, synthesis, Pd(0) coupling.
A cycloaddition approach to the functionalized tricyclo[9.3.1.03,8]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. Keywords: Taxol®, Diels–Alder, synthesis, diterpene, alkaloid.