Accessing 1,8-Naphthyridone-3-carboxylic Acid Derivatives and Application to the Synthesis of Amfonelic Acid

1,8-Naphthyridone-3-carboxyl is the core structure of several on-market antibacterial drugs. It has prompted significant interest from the synthetic community. Here, we report a practical synthesis of diversely functionalized 1,8-naphthyridone-3-carboxylic acid derivatives starting from readily available and inexpensive nicotinic acid derivatives. All key steps have been optimized. Furthermore, the usefulness of this protocol has been exemplified by the first synthesis of amfonelic acid.

Recent advances in transition-metal-catalyzed carbene insertion to C-H bonds

C-H functionalization has been emerging as a powerful method to establish carbon-carbon and carbon-heteroatom bonds. Many efforts have been devoted to transition-metal-catalyzed direct transformations of C-H bonds. Metal carbenes generated in situ from transition-metal compounds and diazo or its equivalents are usually applied as the transient reactive intermediates to furnish a catalytic cycle for new C-C and C-X bond formation. Using this strategy compounds from unactivated simple alkanes to complex molecules can be further functionalized or transformed to multi-functionalized compounds. In this area, transition-metal-catalyzed carbene insertion to C-H bonds has been paid continuous attention. Diverse catalyst design strategies, synthetic methods, and potential applications have been developed. This critical review will summarize the advance in transition-metal-catalyzed carbene insertion to C-H bonds dated up to July 2021, by the categories of C-H bonds from aliphatic C(sp³)-H, aryl (aromatic) C(sp²)-H, heteroaryl (heteroaromatic) C(sp²)-H bonds, alkenyl C(sp²)-H, and alkynyl C(sp)-H, as well as asymmetric carbene insertion to C-H bonds, and more coverage will be given to the recent work. Due to the rapid development of the C-H functionalization area, future directions in this topic are also discussed. This review will give the authors an overview of carbene insertion chemistry in C-H functionalization with focus on the catalytic systems and synthetic applications in C-C bond formation.

Pd and photoredox dual catalysis assisted decarboxylative ortho-benzoylation of N-phenyl-7-azaindoles

Directing group assisted decarboxylative ortho-benzoylation of N-aryl-7-azaindoles with α-keto acids has been achieved by synergistic visible light promoted photoredox and palladium catalysis. The approach tenders rapid entry to aryl ketone...

Copper-Catalyzed Oxidative Dehydrogenative Reaction of Quinoline-N-Oxides with Donor-Acceptor Cyclopropanes: Installation of a Tertiary Alkyl Motif at C2 Position

A copper-catalyzed oxidative dehydrogenative reaction of quinoline N-oxides with donor-acceptor cyclopropanes has been demonstrated to construct C2-alkylated quinolines containing a γ-keto diester motif. The use of molecular oxygen as an oxidant, excellent site-selectivity, and good functional group tolerance are the important features in this process. The preliminary mechanistic studies demonstrate that the catalyst plays a dual role as a Lewis acid and a redox catalyst.

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

Quinoline is a versatile heterocycle that is part of numerous natural products and countless drugs. During the last decades, this scaffold also became widely used as ligand in organometallic catalysis. Therefore, access to functionalized quinolines is of great importance and continuous efforts have been made to develop efficient and regioselective synthetic methods. In this regard, C-H functionalization through transition metal catalysis, which is nowadays the Graal of organic green chemistry, represents the most attractive strategy. We aim herein at providing a comprehensive review of methods that allow site-selective metal-catalyzed C-H functionalization of quinolines, or their quinoline N-oxides counterparts, with a specific focus on their scope and limitations, as well as mechanistic aspects if that accounts for the selectivity.

Copper-Catalyzed Regioselective Coupling of Tosylhydrazones and 2-Pyridones: A Strategy for the Production of N-Alkylated Compounds

The highly regioselective N-alkylation reaction of 2-pyridones was achieved through hydrazone chemistry, especially for substrates with bulky secondary alkyl groups. Described herein is a copper-catalyzed coupling reaction of pyridone derivatives with tosylhydrazones.

The intramolecular reaction of acetophenone N-tosylhydrazone and vinyl: Brønsted acid-promoted cationic cyclization toward polysubstituted indenes

In the presence of TsNHNH2, a Brønsted acid-promoted intramolecular cyclization of o-(1-arylvinyl) acetophenone derivatives was developed, leading to polysubstituted indenes with complexity and diversity in moderate to excellent yields. In sharp contrast with either the radical or carbene involved cyclization of aldehydic N-tosylhydrazone with vinyl, a cationic cyclization pathway was involved, where N-tosylhydrazone served as an electrophile and alkylation reagent during this transformation.

Recent Advances in Microwave-Assisted Copper-Catalyzed Cross-Coupling Reactions

Cross-coupling reactions furnishing carbon–carbon (C–C) and carbon–heteroatom (C–X) bond is one of the most challenging tasks in organic syntheses. The early developed reaction protocols by Ullmann, Ullman–Goldberg, Cadiot–Chodkiewicz, Castro–Stephens, and Corey–House, utilizing elemental copper or its salts as catalyst have, for decades, attracted and inspired scientists. However, these reactions were suffering from the range of functional groups tolerated as well as severely restricted by the harsh reaction conditions often required high temperatures (150–200 °C) for extended reaction time. Enormous efforts have been paid to develop and achieve more sustainable reaction conditions by applying the microwave irradiation. The use of controlled microwave heating dramatically reduces the time required and therefore resulting in increase in the yield as well as the efficiency of the reaction. This review is mainly focuses on the recent advances and applications of copper catalyzed cross-coupling generation of carbon–carbon and carbon–heteroatom bond under microwave technology.

The microwave-assisted syntheses and applications of non-fused single-nitrogen-containing heterocycles

Microwave technology has emerged as a great tool for the efficient synthesis of organic compounds and it provides opportunities for chemists to achieve chemical transformations that tend to be challenging using classical approaches. Additionally, N-heterocycles are well-known for their medicinal/biological significance, along with their applications as excellent building blocks in chemical synthesis. The dominance of N-heterocycles in drug molecules and other pharmacological agents makes them attractive scaffolds, which encourages chemists to develop a wide range of strategies towards the greener synthesis and functionalization of these heterocycles. In this regard, we have collated and discussed literature relating to the microwave-assisted synthesis and the modification of non-(benzo)fused single-nitrogen-containing N-heterocycles from the past decade. The role of the microwave technique and its benefits over the conventional approach have also been emphasized in terms of overall reaction efficiency, reaction time, yield, reduced side-product generation, neat and clean reactions, chemo-/regio-/enantio-selectivity, and the use of mild reagents/reaction conditions to achieve the objectives of green and sustainable chemistry.

Transition-metal- and oxidant-free three-component reaction of quinoline N-oxides, sodium metabisulfite and aryldiazonium tetrafluoroborates via a dual radical coupling process

A convenient and straightforward three-component transformation of quinoline N-oxides, sodium metabisulfite and aryldiazonium tetrafluoroborates has been developed, providing the target products in moderate to good yields. Compared with previous studies, the present methodology avoids the use of transition-metal catalysts and excess oxidants, providing a simple and practical alternative approach for the construction of 2-sulfonylquinolines. Control experiments indicate that a dual radical coupling process is responsible for this reaction.

Copper(i)-catalyzed benzylation of triazolopyridine through direct C-H functionalization

A general and efficient copper-catalyzed benzylation reaction of triazolopyridine with N-tosylhydrazones was developed. This reaction forms a C(sp²)-C(sp³) bond through cross-coupling, and represents an exceedingly practical method to afford 3-benzylated triazolopyridines in moderate to good yields. A proposed mechanistic pathway underlying this reaction was outlined. This catalytic transformation should enable broad synthetic applications in functionalization chemistry, allowing the synthesis of new pharmaceutically relevant triazolopyridine derivatives.

Development of pyrazole and spiropyrazoline analogs as multifunctional agents for treatment of Alzheimer's disease

Cholinergic hypothesis of Alzheimer's disease has been advocated as an essential tool in the last couple of decades for the drug development. Here in, we report de novo fragment growing strategy for the design of novel 3,5-diarylpyrazoles and hit optimization of spiropyrazoline derivatives as acetyl cholinesterase inhibitors. Both type of scaffolds numbering forty compounds were synthesized and evaluated for their potencies against AChE, BuChE and PAMPA. Introduction of lipophilic cyclohexane ring in 3,5-diarylpyrazole analogs led to spiropyrazoline derivatives, which facilitated and improved the potencies. Compound 44 (AChE = 1.937 ± 0.066 µM; BuChE = 1.166 ± 0.088 µM; hAChE = 1.758 ± 0.095 µM; P_e = 9.491 ± 0.34 × 10^-6 cm s¹) showed positive results, which on further optimization led to the development of compound 67 (AChE = 0.464 ± 0.166 µM; BuChE = 0.754 ± 0.121 µM; hAChE = 0.472 ± 0.042 µM; P_e = 13.92 ± 0.022 × 10^-6 cm s¹). Compounds 44 and 67 produced significant displacement of propidium iodide from the peripheral anionic site (PAS) of AChE. They were found to be safer to MC65 cells and decreased metal induced Aβ_1-42 aggregation. Further, in-vivo behavioral studies, on scopolamine induced amnesia model, the compounds resulted in better percentage spontaneous alternation scores and were safe, had no influence on locomotion in tested animal groups at dose of 3 mg/kg. Early pharmacokinetic assessment of optimized hit molecules was supportive for further drug development.

AgBF4-catalyzed deoxygenative C2-amination of quinoline N-oxides with isothiocyanates

A general, effective and convenient protocol for the direct synthesis of various 2-aminoquinolines (39 examples) through AgBF₄-catalyzed amination of quinoline N-oxides with isothiocyanates under base-, oxidant-free and mild conditions was developed.

Cu-Catalyzed carbamoylation versus amination of quinoline N-oxide with formamides

Carbamoylation and amination of quinoline with formamides was developed via copper-catalyzed C–C and C–N bond formations.

Rapid Synthesis of N-Tosylhydrazones under Solvent-Free Conditions and Their Potential Application Against Human Triple-Negative Breast Cancer

Some N-tosylhydrazone derivatives were effectively synthesized under solvent-free conditions by using a grinding method at room temperature. The short reaction time, clean and mild process with simple workup and easy purification of the target compounds were salient features of the present protocol, which enables straightforward access to N-tosylhydrazones. Among the tosylhydrazone derivatives evaluated, compound 3 l exhibits excellent apoptosis-promoting and anticancer potential against triple-negative breast cancer (TNBC) cell lines. This research shows that our synthesized compound 3 l may be a desirable and effective therapeutic drug against TNBC.

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

Cyano-Sacrificial (Arylthio)arylamination of Quinoline and Isoquinoline N-Oxides Using N-(2-(Arylthio)aryl)cyanamides

A copper(I)-catalyzed regioselective arylthio-arylamination of quinoline and isoquinoline N-oxides has been achieved at the expense of a cyano (CN) group from N-(2-(arylthio)aryl)cyanamides. This reductive amination proceeds in one pot at 80 °C in the absence of any additives. This is a unique demonstration of aryl cyanamides serving as arylaminating agents on quinoline/isoquinoline N-oxides with concurrent autoreduction of N-oxide.

RhIII -Catalyzed Direct C8-Arylation of Quinoline N-Oxides using Diazonaphthalen-2(1H)-ones: A Practical Approach towards 8-aza BINOL

An efficient Rh^III -catalyzed redox-neutral method for the direct C8-arylation of quinoline N-oxides using diazonaphthalen-2(1H)-one as coupling partner has been demonstrated. The developed method is simple, scalable and straightforward with a wide range of substrate scope. The applicative potential was extended with a late-stage functionalization and straightforward synthesis of 8-azaBINOL derivative. A plausible reaction pathway was proposed after carrying out preliminary control studies.

Metal-free deoxygenative sulfonylation of quinoline N-oxides with sodium sulfinates via a dual radical coupling process

The first example of a metal- and reductant-free deoxygenative sulfonylation of quinoline N-oxides with sodium sulfinates via a dual radical coupling process is reported.

GO–Cu7S4 catalyzed ortho-aminomethylation of phenol derivatives with N,N-dimethylbenzylamines: site-selective oxidative CDC

An efficient ortho-selective C–H aminomethylation of phenols and naphthols with N,N-dimethylbenzylamines using a GO–Cu₇S₄ nanocatalyst is reported.

Transition-Metal-Catalyzed Cross-Couplings through Carbene Migratory Insertion

Transition-metal-catalyzed cross-coupling reactions have been well-established as indispensable tools in modern organic synthesis. One of the major research goals in cross-coupling area is expanding the scope of the coupling partners. In the past decade, diazo compounds (or their precursors N-tosylhydrazones) have emerged as nucleophilic cross-coupling partners in C-C single bond or C═C double bond formations in transition-metal-catalyzed reactions. This type of coupling reaction involves the following general steps. First, the organometallic species is generated by various processes, including oxidative addition, transmetalation, cyclization, C-C bond cleavage, and C-H bond activation. Subsequently, the organometallic species reacts with the diazo substrate to generate metal carbene intermediate, which undergoes rapid migratory insertion to form a C-C bond. The new organometallic species generated from migratory insertion may undergo various transformations. This type of carbene-based coupling has proven to be general: various transition metals including Pd, Cu, Rh, Ni, Co, and Ir are effective catalysts; the scope of the reaction has also been extended to substrates other than diazo compounds; and various cascade processes have also been devised based on the carbene migratory insertion. This review will summarize the achievements made in this field since 2001.