carboxaldehyde 15 was converted into enone 20via a stereoselective intramolecular pyrylium ylide-alkene cyclization. Subsequent elaboration of 20 into the triflate 23, followed by solvolysis in acidic trifluoroethanol resulted in quantitative rearrangement to the taxane B/C core 24. At a higher oxidation level 27 was ring expanded to give 28. The ring expansion strategy could also be initiated by β-elimination
通过立体选择性分子内
吡啶鎓内鎓盐-烯烃环化反应将取代的
呋喃甲醛15转化为烯酮20。随后将20加工成
三氟甲磺酸酯23,然后在酸性
三氟乙醇中进行溶剂分解,导致
紫杉烷B / C核心24发生定量重排。在较高的氧化
水平下,将27扩环以得到28。环的扩展策略也可以通过3α,10α-氧化桥的β消除来引发。用MeOH在回流下处理50,得到52。7-氧基系列中的类似转化导致环B的扩环67,得到68,和75,得到76。