A practical and concise protocol for the efficient synthesis of pyrrolo[1,2-a]quinoxalines from readily available α-amino acids and 2-(1H-pyrrol-1-yl)anilines under transition metal-free conditions has been established. This protocol, which includes the formation of new C-C and C-N bonds, features a wide substrate scope with a broad range of functional group tolerance.
Pyridine is an important structural motif that is prevalent in natural products, drugs, and materials. Methods that functionalize and derivatize pyridines have gained significant attention. Recently, a large number of transition-metal-free reactions have been developed. In this review, we provide a brief summary of recent advances in transition-metal-free functionalization and derivatization reactions of pyridines, categorized according to their reaction modes.1 Introduction2 Metalated Pyridines as Nucleophiles2.1 Deprotonation2.2 Halogen–Metal exchange3 Activated Pyridines as Electrophiles3.1 Asymmetric 2-Allylation by Chiral Phosphite Catalysis3.2 Activation of Pyridines by a Bifunctional Activating Group3.3 Alkylation of Pyridines by 1,2-Migration3.4 Alkylation of Pyridines by [3+2] Addition3.5 Pyridine Derivatization by Catalytic In Situ Activation Strategies3.6 Reactions via Heterocyclic Phosphonium Salts4 Radical Reactions for Pyridine Functionalization4.1 Pyridine Functionalization through Radical Addition Reactions4.2 Pyridine Functionalization through Radical–Radical Coupling Reactions5 Derivatization of Pyridines through the Formation of Meisenheimer-Type Pyridyl Anions6 Conclusion
An iron-promoted method for the construction of pyrrolo[1,2-a]quinoxaline derivatives has been developed. Various solvents with terminal methyl group, including ethers, amines and dimethyl sulfoxide, were utilized as carbon sources for the synthesis.
Carbon–fluorine bond activation of the trifluoromethyl group represents an important approach to fluorine‐containing molecules. While selective defluorinative functionalization reactions of CF3‐containing substrates have been achieved by invoking difluorocarbocation, difluorocarboradical, or difluoroorganometallic species as the key intermediates, the transformations via fluorocarbanion mechanism only achieved limited success. Furthermore, the enantioselective defluorinative transformation of the CF3 group remained a formidable challenge. Here we report a defluorinative functionalization reaction of 4‐trifluoromethylpyridines involving difluoro(pyrid‐4‐yl)methyl anion as the key intermediate, which was developed based upon our previous studies on the N‐boryl pyridyl anion chemistry. In particular, asymmetric defluoroallylation of 4‐trifluoromethylpyridines and ‐pyrimidines could be achieved by using Ir‐catalysis to forge a difluoroalkyl‐substituted chiral center.
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