The Povarov reaction, a formal [4 + 2] cycloaddition between N-aryl imines and electron-rich dienophiles, has been defined as an efficient method to approach tetrahydroquinolines and has been well established in the past decades. In general, electron-rich heterosubstituted alkenes have served as the most popular dienophiles to achieve the exclusive regioselectivity. However, the use of Lewis acids and Brønsted acids as catalysts is required in these transformations, and, to our knowledge, the Povarov reaction of electron-rich heterosubstituted alkynes has not been reported. Here, we disclose a catalyst-free Povarov reaction of formyl-ynamides with anilines for the rapid and practical synthesis of a diverse range of valuable quindolines, which not only represents the first Povarov reaction of ynamides to the best of our knowledge but also constitutes a very rare example of a catalyst-free ynamide cyclization reaction. This formal [1 + 2 + 3] annulation shows a reversed regioselectivity compared with the previous protocols.

Povarov 反应是 N-芳基亚胺和富电子亲二烯体之间的正式 [4 + 2] 环加成反应，已被定义为处理四氢喹啉的有效方法，并且在过去几十年中得到了很好的证实。一般来说，富含电子的杂取代烯烃是最受欢迎的亲二烯体，以实现独特的区域选择性。然而，在这些转化中需要使用路易斯酸和布朗斯台德酸作为催化剂，据我们所知，富电子杂取代炔烃的波瓦罗夫反应尚未见报道。在这里，我们公开了甲酰基-炔酰胺与苯胺的无催化剂 Povarov 反应，用于快速实用地合成各种有价值的喹多啉，据我们所知，这不仅代表了 ynamides 的第一个 Povarov 反应，而且构成了一个非常罕见的无催化剂 ynamide 环化反应的例子。与以前的协议相比，这种正式的 [1 + 2 + 3] 环化显示出反向的区域选择性。