Development of useful sequential cyclization of acrylate derivatives and applications to bioactive natural products synthesis

许多努力已作出生产双环环戊酮，不仅考虑到其丰富的性质，而且它们的用途作为多功能的合成基石。串联还原偶联- dieckmann缩合反应是一种一步反应，可以有效地从丙烯酸酯衍生物（α，β-不饱和酯）中生产氧环戊烷羧酸盐。电加氢二聚化和金属诱导的肉桂酸衍生物的环化是通常用于这一目的的方法，但没有一种方法被证明能以分子内的方式产生双环氧环戊anecarboxylate。建立了在微量甲醇存在下，用单电子转移试剂SmI_2从简单的双-α，β-不饱和酯一步合成双环[4.3.0]壬烷-8-酮和双环[3.3.0]辛烷-3-酮的有效直接工艺。该反应还合成了严重应变的双环[3.3.0]辛烷翘曲反环体系和三环酮酯，但未能生成双环[5.3.0]癸烷-9- 1和双环[6.3.0]十一烷-10- 1。在制备这些体系的过程中，通过Sm（II）诱导的顺序还原断裂- dieckmann缩合反应，开发了易于从相应的环烯烃或丙烯酸酯衍生物中获得的1,2-环丁二羧酸酯的新型扩环反应。该反应是环丁烷通过串联还原裂解-迪克曼缩合转化为环戊烷的第一个实例。此外，以碘化钐诱导丙烯酸酯衍生物环化为关键步骤，进行了三醌型倍半萜烯、水乳素烯、榄香烯型倍半萜烯、榄香烯-8β、12-内酯的正式全合成和赤霉素A_1的全合成。

Numerous efforts have been made to produce bicyclic cyclopentanones, not only in consideration of their abundance in nature, but also their usefulness as versatile synthetic building blocks. The tandem reductive coupling-Dieckmann condensation reaction has been found quite useful as a one-step process for effectively producing oxacyclopentanecarboxylates from acrylate derivatives (α,β-unsaturated esters). Electrohydrodimerization and metal-induced cyclization of cinnamate derivatives are methods generally applied for this purpose but to none has been shown to produce in an intramolecular manner bicyclic oxacyclopentanecarboxylate. The authors established an effective and direct one-step process for obtaining bicyclo[4.3.0]nonan-8-ones and bicyclo[3.3.0]octan-3-ones from simple bis-α,β-unsaturated esters using one electron transfer reagent SmI_2 in the presence of methanol in trace amount. Severely strained bicyclo[3.3.0]octane warped trans ring system and tricyclic keto esters were also synthesized by the reaction, but the formation of bicyclo[5.3.0]decan-9-ones and bicyclo[6.3.0]undecan-10-ones failed to occur. For the preparation of these system, the novel ring-expansion reaction of 1,2-cyclobutanedicarboxylates, readily accessible from the corresponding cycloalkenes or acrylate derivatives, via Sm(II)-induced sequential reductive fragmentation-Dieckmann condensation was developed. This reaction is the first instance of the transformation of cyclobutanes to cyclopentanes via tandem reductive fragmentation-Dieckmann condensation. Forthermore, the formal total syntheses of triquinane-type sesquiterpines, hirustene, and eleman-type sesquiterpenoid, eleman-8β,12-olide, and the total synthesis of gibberellin A_1 were conducted with Sm(II) iodide-induced cyclization of acrylate derivatives as key steps.