To elucidate the structure of the new natural product spirodionic acid, which has three stereogenic centers of hitherto unknown configuration, two 4-ethenylspiro[4.5]dec-6-en-1,8-diones with opposite relative configuration at C4 and C5 were prepared. The first access involved the synthesis of 3-ethenyl-2-formylcyclopentanone (8) using a three-component coupling process. A sequence of Michael addition to penten-3-one (7) and intramolecular aldol condensation then led to the highly selective formation of the 4S*,5S*-configured spirocycle 5. In contrast, a selective spiroannelation of a cyclohexenone ring was accomplished by a novel type of twofold Michael addition to the dialkenyl ketone 11 with subsequent dehydrogenation to furnish the 4S*,5R*-configured spirocycle 25. Diastereoselective methylation and oxidative degradation then completed a highly efficient synthesis of the natural product as prerequisite for the assignment of its absolute configuration.

中文翻译：

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螺环酸，一种来自链霉菌属的新型代谢物，第2部分：通过双重迈克尔加成作为选择性的螺旋退火策略，实现了全合成。

为了阐明具有三个迄今未知构型的立体异构中心的新天然产物螺二酸的结构，制备了两个在C4和C5处相对构型相反的4-乙烯基螺[4.5] dec-6-en-1,8-二酮。 。首次接触涉及使用三组分偶联方法合成3-乙烯基-2-甲酰基环戊酮（8）。然后，对戊烯-3-一（7）进行迈克尔加成和分子内羟醛缩合的序列导致高度选择性地形成了4S *，5S *构型的螺环5。相反，环己烯酮环的选择性螺杂环化是通过向二烯基酮11中添加一种新型的双键迈克尔加成反应，随后进行脱氢反应，以提供4S *，5R *构成的螺环25。