Indole is a very common structural motif in alkaloids, and a number of them feature remarkable bioactive properties. Due to its relevant role in medicinal chemistry and the pharma-industry, many methods for indole synthesis have been developed, but only a few of them exploit the [4 + 2] approach. Recently a successful attempt at indole and carbazole formation via a formal gold mediated [4 + 2] addition of a diyne to pyrrole and indole rings has been reported by Ohno. A number of intriguing features observed in this reaction are however left to be resolved. We study here the mechanism of the Au-catalyzed reaction of 1,3-diynes with pyrrole and indole rings leading to substituted indoles and carbazoles, respectively. The reaction pathways are found to be significantly more complex than we had anticipated, for instance, in the case of the formation of carbazoles, one competitive route involves the formation of an unexpected spirane intermediate that evolves via a 1,2-alkenyl migration. Beyond this complexity, the current study also serves to highlight the importance of fundamental steps that are often disregarded as kinetically irrelevant, such as the protodeauration of reaction intermediates.

中文翻译：

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原型脱氢在1,3-二炔与吡咯和吲哚形成复杂杂环的金催化反应中的关键作用

吲哚是生物碱中非常常见的结构基序，其中许多具有显着的生物活性。由于其在药物化学和制药工业中的相关作用，已经开发了许多吲哚合成方法，但只有少数采用[4 + 2]方法。最近，在吲哚和咔唑形成一个成功的尝试通过大野（Ohno）报道了在吡咯和吲哚环中由金介导的二炔[4 + 2]的正式加成。然而，该反应中观察到的许多有趣特征尚待解决。我们在这里研究1，3-二炔与吡咯和吲哚环分别导致取代的吲哚和咔唑的Au催化反应机理。发现反应途径比我们预期的要复杂得多，例如，在形成咔唑的情况下，一种竞争性途径涉及形成意外的螺环中间体，该中间体通过1,2-烯基的迁移。除了这种复杂性之外，当前的研究还强调了通常被认为与动力学无关的基本步骤的重要性，例如反应中间体的原化。