Multisubstituted benzofurans/indoles are a critical class of compounds in the fields of pharmaceuticals and natural products. A useful method of preparing 2-substituted benzofurans/indoles is the Pd-catalyzed Sonogashira coupling of 2-halophenols/2-haloanilines and terminal alkynes, followed by cyclization. For the syntheses of multisubstituted benzofurans/indoles, the use of multichlorinated phenols/anilines as coupling partners is powerful because the synthetic steps required are reduced and all dichlorophenol and dichloroaniline positional isomers are commercially available and inexpensive. However, their use in benzofuran/indole synthesis is limited because of their low reactivity compared with those of the corresponding iodo or bromo compounds. Furthermore, site-selective Sonogashira coupling at the 2-position of the multihalogenated phenols/anilines is sterically and electronically challenging. To overcome these problems, dihydroxyterphenylphosphine (DHTP) has been developed as a ligand that enables the highly ortho-selective Sonogashira coupling of 2-chlorophenols/2-chloroanilines with terminal alkynes. Using the Pd–DHTP catalyst, chlorinated benzofurans/indoles are successfully obtained, which are easily converted to other derivatives by substitution of the chloro group. In this review, we summarize this and related studies to demonstrate the utility of this method.

中文翻译：

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钯催化位点选择性 Sonogashira 偶联多氯代苯酚/苯胺合成多取代苯并呋喃/吲哚

多取代的苯并呋喃/吲哚是药物和天然产物领域中的一类关键化合物。制备 2-取代的苯并呋喃/吲哚的有用方法是 Pd 催化的 Sonogashira 偶联 2-卤代苯酚/2-卤代苯胺和末端炔烃，然后进行环化。对于多取代的苯并呋喃/吲哚的合成，使用多氯代苯酚/苯胺作为偶联伙伴是强大的，因为所需的合成步骤减少了，并且所有二氯苯酚和二氯苯胺位置异构体都是可商购的且价格低廉。然而，它们在苯并呋喃/吲哚合成中的使用受到限制，因为与相应的碘或溴化合物相比，它们的反应性较低。此外，在多卤代苯酚/苯胺的 2 位进行位点选择性 Sonogashira 偶联在空间和电子方面具有挑战性。为了克服这些问题，已开发出二羟基三联苯膦（DHTP）作为配体，使高度2-氯酚/2-氯苯胺与末端炔烃的邻位选择性 Sonogashira 偶联。使用 Pd-DHTP 催化剂，成功地获得了氯化苯并呋喃/吲哚，通过氯基的取代，它们很容易转化为其他衍生物。在这篇综述中，我们总结了这项研究和相关研究，以证明这种方法的实用性。