Research Progress on N-Heterocyclic Carbene Catalyzed Reactions for Synthesizing Ketones through Radical Mechanism

Abstract NHC-catalyzed radical cross-coupling reactions have been recently developed; they provide an efficient method to access ketones from aldehydes or carboxylic acid derivatives with sp3-hybridized carbon radical precursors. This reaction has indirectly solved the limitations in the scope of coupling partners in NHC umpolung catalyzed reactions of aldehydes. In this short review, we present some recent advances in NHC-catalyzed radical reactions, with a focus on the construction of the C–C(CO) bond. 1 Introduction 2 Oxidative Generation of NHC-Derived Ketyl Radical 2.1 NHPI Redox-Active Esters 2.2 Katritzky Pyridinium Salts 2.3 Alkyl Halides 2.4 Aryl Halides 2.5 Compounds Containing N–O Bond 2.6 Diazo Esters 2.7 Others 3 Reductive Generation of NHC-Derived Ketyl Radical 3.1 Hantzsch Esters 3.2 Sulfinates 3.3 Electron-Rich Arenes 3.4 Amines 3.5 Organoborane Reagents 4 Conclusion