Difunctionalization of Acrylamides through C–H Oxidative Radical Coupling: New Approaches to Oxindoles

Oxindoles are an important class of heterocycles with unique biological activity that are found prevalently in numerous natural products and biologically active compounds. For these reasons, much attention has been given to the development of efficient methods for the preparation of such compounds. Traditionally, the practical approaches for the synthesis of oxindoles include the condensation of anilines with carbonyl compounds, such as diethyl ketomalonate, oxalyl chloride, or chloral hydrate, mediated by strong acids or bases. Recently, a step- and atom-economic C–H activation strategy was illustrated to access oxindoles through the difunctionalization of activated alkenes for these purposes. However, many of these transformations suffer from the cost of the transition-metal catalytic systems and/or limited substrate scope. In this review, we describe the recent studies of the difunctionalization of activated alkenes for the synthesis of diverse functionalized oxindoles that involves C–H oxidative radical coupling in the presence of an oxidant. These transformations are initiated either by the carbon radical resulting from the split of the carbon–hydrogen bond (1,2-dicarbofunctionalization) or by the carbon or heteroatom radical arising from the cleavage of the carbon–heteroatom (1,2-dicarbofunctionalization) or heteroatom–heteroatom bond (1,2-carboheterofunctionalization). Importantly, these C–H oxidative radical coupling transformations are generally performed with readily available oxidants and/or inexpensive iron or copper catalysts under neutral reaction conditions. 1 Introduction 2 Synthesis of Oxindoles via 1,2-Dicarbofunctionalization of Alkenes 2.1 1,2-Alkylarylation 2.2 1,2-Aryltrifluoromethylation 2.3 1,2-Carbonylarylation 3 Synthesis of Oxindoles via 1,2-Carboheterofunctionalization of Alkenes 3.1 1,2-Azidoarylation or 1,2-Arylnitration 3.2 1,2-Arylsulfonylation 3.2 1,2-Arylphosphorylation 4 Conclusion