4+1 annulation based reaction offers a versatile tool for the synthesis of 5-membered carbo/heterocycles. Recent advances of 4+1 annulation through transition-metal-catalyzed C–H bond activation have provided straightforward and widely applicable alternatives to the traditional methods. In particular, the redox-neutral strategies emerged in the past 5 years overcome the inherent disadvantages caused by the external oxidant which are generally required in the early protocols to regenerate the active catalyst, such as limited substrate scope, harsh reaction conditions and generation of stoichiometric by-products. Progress in oxidant-free 4+1 annulations through transition-metal-catalyzed C–H bond activation are discussed in this review until September 2017.

基于4 + 1环空的反应为5元碳/杂环的合成提供了一种多功能的工具。通过过渡金属催化的C–H键活化4 + 1环空的最新进展为传统方法提供了直接且广泛适用的替代方法。尤其是，过去5年出现的氧化还原中性策略克服了由外部氧化剂引起的固有缺点，这些缺点在早期规程中通常是再生活性催化剂所必需的，例如受限制的底物范围，苛刻的反应条件和化学计量的产生。副产品。到2017年9月，本文讨论了通过过渡金属催化的C–H键活化实现无氧化剂4 + 1环化的进展。