The widespread use of halogen-based reagents in organic synthesis is well known. Hypervalent halogens (oxidation states III and V) have been explored to a significant extent. Among them, hypervalent iodine reagents have found major use and applications. In contrast, understanding of the reactivity of halogen(I) species in the presence of Lewis bases, and their reaction mechanisms, are very limited. This microreview sheds light on the importance of halogen(I) species and their applications in organic synthesis. In commercially available halogen(I) precursors such as N-halosuccinimides, the halogen atom is attached to the nitrogen atom through a covalent bond with low electrophilicity and thus low reactivity. Interestingly, the reactivity increases if the electrophilic halogen(I) atom is attached to a Lewis base through a polarized covalent bond. The halogen-bonding interaction between the Lewis base and the halonium ion (or halonium ion equivalent) results in highly reactive and thermodynamically stable halogen(I) intermediates that act as versatile reagents. This microreview unravels the evolution of the unstable halogen(I) intermediates to become versatile reagents.

中文翻译：

---

路易斯碱配位卤素 (I) 中间体在有机合成中的作用：从不稳定中间体到多功能试剂的旅程

卤素试剂在有机合成中的广泛使用是众所周知的。高价卤素（氧化态 III 和 V）已被大量研究。其中，高价碘试剂已发现主要用途和应用。相比之下，对卤素 (I) 物质在路易斯碱存在下的反应性及其反应机制的了解非常有限。这篇微观评论阐明了卤素 (I) 物种的重要性及其在有机合成中的应用。在市售的卤素 (I) 前体（例如 N-卤代琥珀酰亚胺）中，卤素原子通过共价键连接到氮原子上，亲电性低，因此反应性低。有趣的是，如果亲电卤素 (I) 原子通过极化共价键连接到路易斯碱，则反应性会增加。路易斯碱和卤离子（或卤离子等价物）之间的卤键相互作用产生了高反应性和热力学稳定的卤素 (I) 中间体，可作为通用试剂。这篇微观评论揭示了不稳定卤素 (I) 中间体成为通用试剂的演变过程。