2-Oxindole unit is one of the most important scaffolds found in several alkaloids, natural products, antitumor agents, pharmaceutically important compounds, etc. Molecules containing the 2- oxindole moiety were first isolated from the cat claw plant, widely distributed in the Amazon jungle. It has now been demonstrated that these molecules are present in a wide range of chemicals derived from plant sources. The capacity of 2-oxindole to be altered by various chemical groups to provide unique biological activities can be attributed to its function as a chemical framework for creating and developing biological medications. Since the development of its first synthetic methodology, several research groups have developed protocols for producing 2-oxindole core and its bioactive derivatives. These include the traditional method and the transition/non-transition metal-catalyzed pathway for the synthesis of C3-non-substituted/C3-mono-substituted/C3-di-substituted core. Among those, C3-substitution-free 2-oxindole core synthesis is quite a challenging task, as C3-centre is very reactive. Syntheses of C3-substitution-free 2-oxindole cores have been less explored compared to other substituted 2-oxindole derivatives. In this review article, we have mainly focused on showcasing the transition metal-catalyzed synthetic methodology for the synthesis of 2-oxindoles with no substitution at C3-centre.

中文翻译：

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过渡金属催化合成无C3取代的2-羟吲哚衍生物的最新进展

2-羟吲哚单元是在多种生物碱、天然产物、抗肿瘤剂、药学上重要的化合物等中发现的最重要的支架之一。含有2-羟吲哚部分的分子首先从广泛分布于亚马逊丛林的猫爪植物中分离出来。 。现在已经证明这些分子存在于多种植物来源的化学物质中。2-羟吲哚能够被各种化学基团改变以提供独特的生物活性，这可归因于其作为创建和开发生物药物的化学框架的功能。自从开发出第一种合成方法以来，多个研究小组已开发出生产 2-oxindole 核心及其生物活性衍生物的方案。其中包括传统方法和过渡/非过渡金属催化途径合成C3-未取代/C3-单取代/C3-二取代核。其中，C3无取代的2-羟吲哚核心合成是一项相当具有挑战性的任务，因为C3中心的反应性非常强。与其他取代的 2-羟吲哚衍生物相比，无 C3 取代的 2-羟吲哚核心的合成研究较少。在这篇综述文章中，我们主要重点展示了过渡金属催化合成 C3 中心无取代的 2-羟吲哚的合成方法。