The convergent syntheses of the C(1â32) and C(33â46) domains of phorboxazole B are described. An iterative cyclocondensation strategy exploited the Jacobsen hetero-DielsâAlder (HDA) reaction as a platform for the synthesis of both the C(5â9) and C(11â15) tetrahydropyran rings. The use of 2-silyloxydiene coupling partners bearing an increasing resemblance to the phorboxazole skeleton was found to lead to a reduction in diastereoselectivity, however, in the case of the C(11â15) ring. The coupling of aldehyde 21 and 2-silyloxydiene 20 by this route provided a C(1â32) fragment which was elaborated to the macrolide core of phorboxazole B. The synthesis of the C(33â46) domain involved a NozakiâKishi coupling of aldehyde 31 and vinyl iodide 39. The syntheses of 31 and 39 were highly diastereoselective: an Evans [Cu(Ph-pybox)](SbF6)2-catalysed Mukaiyama aldol reaction formed the cornerstone of the synthesis of 31 whilst a NagaoâFujita acetate aldol reaction provided a convenient means of installing the sole stereogenic centre of 39.
报道了phorboxazole B的C(1–32)和C(33–46)区域的汇聚式合成。一种迭代环加成策略利用了Jacobsen的杂Diels–Alder (H
DA)反应作为合成C(5–9)和C(11–15)
四氢吡喃环的平台。使用越来越类似于phorboxazole骨架的2-
硅氧基二烯作为偶联伙伴,发现导致了对映选择性的降低,但在C(11–15)环的情况下。通过这种方法将醛21和2-
硅氧基二烯20偶联,得到了C(1–32)片段,进而发展为phorboxazole B的大环内酯核心。C(33–46)区域的合成涉及醛31和
乙烯基碘39的Nozaki–Kishi偶联。31和39的合成高度对映选择性:Evans [Cu(Ph-pybox)](SbF6)2催化的Mukaiyama Aldol反应构成了31合成的基础,而Nagao–Fujita
乙酸盐Aldol反应为39唯一手性中心的安装提供了一种便捷的方法。