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.
描述了一种用于功能化紫杉醇中含有的三环[9.3.1.0^3,8]戊二十烯骨架的环加成方法。将环己烯酮13转化为腈醛24,然后通过顺序亲核加成将二烯和乙炔侧链连接到其中。去除三甲基硅保护基和Dess-Martin氧化生成三烯35。微波辅助热环化立体选择性地生成三环酮36,其结构经过与2,3-二氯-5,6-二氰基-1,4-苯醌(DDQ)反应转化为芳香系统37进一步确定。开发了一个环氧化序列,引入了所需的环加成策略C13醇47的对映异构体。另外,烯丙基氧化(CrO3, 3,5-二甲基吡唑)生成了C13酮49。关键词:紫杉醇,迪尔斯-阿尔德,合成,二萜,生物碱。