A Copper-Catalyzed Aerobic [1,3]-Nitrogen Shift through Nitrogen-Radical 4-exo-trig Cyclization

Visible-Light-Induced α,γ-C(sp3)-H Difunctionalization of Piperidines

Herein, we describe a novel protocol for visible-light-induced α,γ-C(sp³)-H difunctionalization of piperidines. This redox-neutral, atom-economical protocol, which exhibits a broad substrate scope and good functional group compatibility, constitutes a concise, practical method for constructing piperidine-containing bridged-ring molecules. Preliminary mechanistic studies indicated that highly regioselective activation of the inert γ-C(sp³)-H bond of piperidines was achieved through a 1,5-hydrogen atom transfer reaction of a nitrogen radical generated in situ.

Copper-catalyzed aerobic benzylic C(sp3)-H lactonization of 2-alkylbenzamides via N-centered radicals

Herein, we describe the copper-catalyzed aerobic C(sp³)-H functionalization of 2-alkylbenzamides for the synthesis of benzolactones. This reaction proceeds via 1,5-hydrogen atom transfer of N-centered radicals directly generated by N-H bond cleavage and does not require the synthesis of pre-functionalized N-centered radical precursors or the use of strong stoichiometric oxidants.

Recent developments in the green synthesis of biologically relevant cinnolines and phthalazines

Both cinnolines and phthalazines are heterocyclic compounds which have a wide range of biological activities and pharmacological profiles. This work represents the recent advances in the green synthesis of cinnolines and phthalazines as 1,2 and 2,3-diazanaphalenes were cited. The docking studies and mode of action for key scaffolds were also reported.

Cobalt-catalyzed C(sp3)-H bond functionalization to access indole derivatives

Herein, we develop an efficient method of cobalt-catalyzed C(sp3)-H bond functionalization to synthesize indole derivatives. The highlight of this protocol is accomplished by the sequential C-H activation. This “cobalt/ organic...

Recent Advances in Copper-Catalyzed C-N Bond Formation Involving N-Centered Radicals

C-N bonds are pervasive throughout organic-based materials, natural products, pharmaceutical compounds, and agricultural chemicals. Considering the widespread importance of C-N bonds, the development of greener and more convenient ways to form C-N bonds, especially in late-stage synthesis, has become one of the hottest research goals in synthetic chemistry. Copper-catalyzed radical reactions involving N-centered radicals have emerged as a sustainable and promising approach to build C-N bonds. As a chemically popular and diverse radical species, N-centered radicals have been used for all kinds of reactions for C-N bond formation by taking advantage of their inherently incredible reactive flexibility. Copper is also the most abundant and economic catalyst with the most relevant activity for facilitating the synthesis of valuable compounds. Therefore, the aim of the present Review was to illustrate recent and significant advances in C-N bond formation methods and to understand the unique advantages of copper catalysis in the generation of N-centered radicals since 2016. To provide an ease of understanding for the readers, this Review was organized based on the types of nitrogen sources (amines, amides, sulfonamides, oximes, hydrazones, azides, and tert-butyl nitrite).

Radical 1,4/5-Amino Shift Enables Access to Fluoroalkyl-Containing Primary β(γ)-Aminoketones under Metal-Free Conditions

A novel radical 1,4/5-amino shift from the oxygen center of alkene-tethered diphenyl ketoxime ethers to the carbon center to achieve high value-added fluoroalkyl-containing primary β(γ)-amino-ketones is reported. Mechanism studies reveal that the migration is triggered by the alkene addition of fluoroalkyl radical derived from the electron donor-acceptor (EDA) complex of Togni's reagent II or fluoroalkyl iodides and quinuclidine, and involves a unique 5(6)-exo-trig cyclization of the carbon-centered radical onto the N-atom of ketoxime ethers followed by a cascade sequence of N-O bond cleavage and dehydrogenation. Notably, besides Togni's reagent II and fluoroalkyl iodides, this protocol is also compatible with other radical precursors to provide various functionalized primary aminoketones.

A radical-mediated multicomponent cascade reaction for the synthesis of azide-biindole derivatives

A radical-mediated, one-pot, multicomponent cascade reaction was developed for the synthesis of azide-biindole derivatives. Mechanistic studies demonstrated that the nitrogen-centred free radical was formed by the reaction of heterocyclic N-H with Cu^II and PIFA and initiated the cascade reaction with indole to obtain the biindole intermediate. The biindole intermediate then reacted with sodium azide in the presence of Cu^II catalyst and PIFA to form the final products. This methodology may be useful for constructing other azido heterocycles.

Recent advances in the synthesis of pyrrolo[1,2-a]indoles and their derivatives

The pyrrolo[1,2-a]indole unit is a privileged heterocycle found in numerous natural products and has been shown to exhibit diverse pharmacological properties. Thus, recent years have witnessed immense interest from the synthesis community on the synthesis of this scaffold. In light of the ever-increasing demand for pyrrolo[1,2-a]indoles in drug discovery, this review provides an overview of recent synthesis methods for the preparation of pyrrolo[1,2-a]indoles and their derivatives. The mechanistic pathway and stereo-electronic factors affecting the yield and selectivity of the product are briefly explained. Furthermore, we have attempted to demonstrate the utility of the developed methods in the synthesis of bioactive molecules and natural products, wherever offered.

One-pot, three-component Fischer indolisation-N-alkylation for rapid synthesis of 1,2,3-trisubstituted indoles

A one-pot, three-component protocol for the synthesis of 1,2,3-trisubstituted indoles has been developed, based upon a Fischer indolisation-indole N-alkylation sequence. This procedure is very rapid (total reaction time under 30 minutes), operationally straightforward, generally high yielding and draws upon readily available building blocks (aryl hydrazines, ketones, alkyl halides) to generate densely substituted indole products. We have demonstrated the utility of this process in the synthesis of 23 indoles, benzoindoles and tetrahydrocarbazoles bearing varied and useful functionality.

Copper-catalyzed oxidative benzylic C-H cyclization via iminyl radical from intermolecular anion-radical redox relay

Base-promoted C-H cleavage without transition metals opens a practical alternative for the one based on noble metals or radical initiators. The resulting carbanion can pass through radical addition to unsaturated bonds like C-N or C-C triple bonds, in which stoichiometric oxidants are needed. When in situ C-H cleavage meets catalytic carbanion-radical relay, it turns to be challenging but has not been accomplished yet. Here we report the combination of base-promoted benzylic C-H cleavage and copper-catalyzed carbanion-radical redox relay. Catalytic amount of naturally abundant and inexpensive copper salt, such as copper(II) sulfate, is used for anion-radical redox relay without any external oxidant. By avoiding using N-O/N-N homolysis or radical initiators to generate iminyl radicals, this strategy realizes modular synthesis of N-H indoles and analogs from abundant feedstocks, such as toluene and nitrile derivatives, and also enables rapid synthesis of large scale pharmaceuticals.

The synthesis of high value heterocycles from cheap starting materials remains challenging. Here, the authors develop a new strategy to realize practical and modular synthesis of N-H indoles and analogs from toluene and nitrile derivatives using naturally abundant copper salt as catalyst.

Metal-free cyclization of unsaturated hydrazones for the divergent assembly of pyrazolones and pyrazolines

An oxidative cyclization of β,γ-unsaturated hydrazones for the divergent assembly of pyrazolones and pyrazolines under metal-free conditions is presented.

Recent Progress in the Transition Metal Catalyzed Synthesis of Indoles

Indole is the most frequently found heterocyclic core structures in pharmaceuticals, natural products, agrochemicals, dyes and fragrances. For about 150 years, chemists were absorbed in finding new and easier synthetic strategies to build this nucleus. Many books and reviews have been written, but the number of new syntheses that appear in the literature, make necessary continuous updates. This reviews aims to give a comprehensive overview on indole synthesis catalyzed by transition metals appeared in the literature in the years 2016 and 2017.