A metal-free protocol utilizing DBU catalysis for post-Ugi amide-ester exchange and Conia-ene double cyclization has been successfully developed, allowing the synthesis of diverse highly functionalized benzo-fused spiroindolines with anti-cancer activities under mild conditions. Remarkably, this methodology demonstrates promising prospects for green chemistry, as it allows for the preparation of the spiroindolines in water. Control experiments indicate that a crucial role of the cyclic imide, specifically ring rigidification, facilitates the subsequent Conia-ene cyclization.

中文翻译：

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通过 DBU 催化的后 Ugi 双环化绿色合成多种生物活性苯并稠合螺吲哚啉

成功开发了一种利用 DBU 催化进行后 Ugi 酰胺酯交换和 Conia-ene 双环化的无金属方案，允许在温和条件下合成具有抗癌活性的多种高功能化苯并稠合螺吲哚啉。值得注意的是，这种方法展示了绿色化学的广阔前景，因为它允许在水中制备螺吲哚啉​​。对照实验表明，环状酰亚胺的关键作用，特别是环刚性化，促进了随后的 Conia-ene 环化。