Nickel-Catalyzed Remote C4–H Arylation of 8-Aminoquinolines

Abstract

A useful and convenient method for C−H bond arylation of 8-aminoquinoline motifs on the remote C4 position was developed. This method shows good functional group tolerance toward various Grignard reagents and aminoquinoline via a nickel catalysis, giving the desired arylated products in good yields. The present method affords an efficient access to construct multisubstituted aminoquinolines.G iven the importance and versatility of quinoline derivatives as bioactive natural products, medicines, functional materials (Figure 1), 1 and directing groups for C− H functionalization in transition-metal-catalyzed reactions, 2 developing highly efficient and environmentally benign protocols for the synthesis of various functionalized quinolines is highly desired. In the past several decades, tremendous progress has been made for the construction of quinoline motifs via cyclization of anilines derivatives 3 or cyclization of substituted alkynes 4 intermolecularly or intramolecularly.However, the above-mentioned methods suffer from drawbacks such as high prefunctionalized starting materials and low selectivity in some cases. 4d An alternative synthetic method for functionalized quinolines is the site-selective modification of readily accessible quinoline frameworks via C−H functionalization. This method provides a quick access to functionalized quinolines. However, the regioselectivity has to be controlled. Many reactions for the C−H bond functionalization of the quinoline core are mainly on the position of C2, 5 C3, 6 C5, 7 and C8, 8 which are easily accessible. However, as for the functionalization of the important C4 position, 1d,e which is relatively less electrophilic (more nucleophilic) among the 8aminoquinioline core, progress is very slow. 9 In recent years, there are several reports concerning the functionalization on the C4 position of pyridine 10 or quinoline motif, 11 which provide some idea for the functionalization of 8-aminoquinoline. However, as for the remote C4−H functionalization of aminoquinolines, only three examples have been disclosed (Scheme 1). 9 In 2014, Zeng et al. reported the first two substrates of Fe-catalyzed remote C4−H allylation of 8aminoquinolines (Scheme 1a). 9a Wu et al. developed phosphonation of 8-aminoquinoline at C4 position via the combination of photocatalysis and transition metal catalysis

Regioselective Functionalization of Quinolines through C-H Activation: A Comprehensive Review

“…Very recently, in 2019, the team of Qiu and Kambe reported their work on the nickel-catalyzed remote C4-H arylation of 8-aminoquinolines, an important class of molecules which is widely represented in biologically active compounds, materials and DG or ligands for metal catalysis ( Scheme 56 ) [ 167 ]. Several reactions have been developed for their C5 functionalization but, to our knowledge, this is the only example where a metal catalyzed C4-H activation pathway is described.…”

Diaryliodonium Salts in Transition‐Metal‐Catalyzed Chelation‐Induced C(sp2/sp3)−H Arylations

“…103/2014 dt. 18.07.2015) and TEQIP-III is greatly acknowledged. Asha Joshi is grateful to NIT Uttarakhand for her fellowship.…”

“…Several arylating agents including aryl halides (chloride, bromide, and iodide) as an electrophile have been employed for the arylation of CÀ H bonds. In addition, some other electrophilic partners like triflates, [13] diazonium and diaryliodonium salt, [14][15] phenols, [16] tosylates, [17] and Grignard reagents [18] etc. have also been utilized for this transformation.…”

On-Demand Electrochemical Synthesis of copper(I) Triflate and Its Application in the Aerobic Oxidation of Alcohols

“…[1][2][3][4] Recent examples show that Ni(OTf)2 displays superior catalytic activity compared to other Ni salts in C-H arylation and C-C coupling reactions. 5,6 Fe II or Fe III triflate salts have performed better than other Fe salts in oxidation, radical addition, and C-O bond silylation. [7][8][9] Despite these representative examples and their widespread use in catalysis, there remain challenges associated with the synthesis of metal triflates, which often involves reacting a metal halide with AgOTf.…”