Symmetrical Bisquinolones via Metal-Catalyzed Cross-Coupling and Homocoupling Reactions

Kinetics and Mechanism of PPh3/Ni-Catalyzed, Zn-Mediated, Aryl Chloride Homocoupling: Antagonistic Effects of ZnCl2/Cl. J Am Chem Soc 2024;146:29913-29927. [PMID: 39420638 PMCID: PMC11528415 DOI: 10.1021/jacs.4c12088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The Ni/PPh3-catalyzed homocoupling of aryl chlorides in DMF using Zn as the stochiometric reducing agent is one of a general class of Ni-catalyzed processes, where the mechanism has been a matter of long-standing debate. This study re-evaluates prior conclusions and insights. NMR spectroscopy is used to identify [(PPh3)2NiII(Ar)Cl] as a key intermediate and to explore the indirect roles of using Zn as the reductant. The [ZnCl2] coproduct is responsible for several features, including a sequential transmetalation pathway involving [ArZnCl]. [ZnCl2] also abstracts halide from [(PPh3)2NiCl2] to generate [NiIICl(DMF)5]+[ZnCl3(DMF)]-, and in doing so, affects the NiII + Ni0 ↔ 2 NiI speciation. [ZnCl2] thus acts as an accelerator and inhibitor, resulting in mildly sigmoidal reaction profiles. When the [ZnCl2] concentration becomes too high or the phosphine ligand concentration too low, catalysis stalls. Turnover is restored by the addition of further phosphine ligand, or chloride ion. In the presence of an exogenous chloride ion, turnover is rapid, again proceeding via [(PPh3)2NiII(Ar)Cl] but via dinuclear metathesis. The generation of [ZnCl3(DMF)]- results in mutually antagonistic effects between [ZnCl2] and [Cl]- such that turnover proceeds via one mechanism or the other, depending on which species is in excess. The intermediacy of [ArZnCl] suggests a solution to the long-standing anomaly that many other reductants were found to be much less effective than Zn in inducing turnover of Ni/PPh3 catalyzed aryl chloride homocoupling in DMF. The use of DMAc as a solvent in place of DMF inhibits stalling through the steric inhibition of mixed metalate generation.

Direct C-H borylation of vinylporphyrins via copper catalysis

A method of direct borylation of vinyl-substituted porphyrinoids (porphyrins and chlorins) has been developed based on the copper catalyzed vinylic C-H activation. Ni(II) complexes of meso- and β-vinylporphyrinoids have been...

Palladium-Catalysed Synthesis and Transformation of Quinolones

Palladium-catalysed reactions have had a large impact on synthetic organic chemistry and have found many applications in target-oriented synthesis. Their widespread use in organic synthesis is due to the mild conditions associated with the reactions together with their tolerance of a wide range of functional groups. Moreover, these types of reactions allow the rapid construction of complex molecules through multiple bond-forming reactions in a single step, the so-called tandem processes. Pd-catalysed reactions have been applied to the synthesis of a large number of natural products and bioactive compounds, some of them of complex molecular structures. This review article aims to present an overview of the most important Pd-catalysed reactions employed in the synthesis and transformations of quinolin-2(1H)-ones and quinolin-4(1H)-ones. These compounds are widely recognized by their diverse bioactivity, being privileged structures in medicinal chemistry and useful structural moieties for the development of new drug candidates. Furthermore, they hold significant interest due to their host⁻guest chemistry; applications in chemical, biochemical and environmental analyses and use in the development of new synthetic methods. In some cases, the quinolone formation step cannot be ascribed to a claimed Pd-catalysed reaction but this reaction is crucial to get the appropriate substrate for cyclization into the quinolone. Herein we present and discuss different economical, efficient and selective synthetic strategies to access quinolone-type compounds.

Synthesis of novel 1,2-bis-quinolinyl-1,4-naphthoquinones: ERK2 inhibition, cytotoxicity and molecular docking studies

Two novel series of N-2,3-bis(6-substituted-4-hydroxy-2-oxo-1,2-dihydroquinolin-3-yl)naphthalene-1,4-diones 3a-d and substituted N-(methyl/ethyl)bisquinolinone triethyl-ammonium salts 4e,f were successfully synthesized. The synthesized compounds were targeted as new candidates to extracellular signal-regulated kinases 1/2 (ERK1/2) with considerable antineoplastic activity. The synthesis involved the reactions of 2 equivalents of 4-hydroxy-2(1H)-quinolinones 1a-f and one equivalent of 1,4-naphthoquinone (2) in a mixture of ethanol/dimethylformamide (1:1) as a solvent and 0.5 mL Et₃N. In the reaction of 6-methyl-4-hydroxyquinolone 1b with 2, a side product 4b of the second series was obtained. In general, the presence of free NH-quinolone gave a single compound of the first series, whereas reaction of N-methyl/ethyl-quinolones 1e,f with 2 enhanced the formation of compounds of the second series. The structures of the new compounds were proved by different spectroscopic techniques such as IR, NMR (2D-NMR) and mass spectra, elemental analysis, and X-ray crystallography. To further elucidate the mechanism of action of these newly synthesized compounds, compounds 3a, 3b, 4e and 4f were selected to investigate for their MAP Kinases pathway inhibition together with molecular docking using ATP-binding site of ERK2. The results revealed that compounds 3a, 3b and 4f inhibited ETS-1 phosphorylation by ERK2 in a dose dependent manner. Also, compound 4f showed highest potency for ERK2 inhibition with ATP-competitive inhibition mechanism which was confirmed by the formation of three hydrogen bond in the molecular docking studies. The synthesized compounds were then tested for their in vitro anticancer activity against the NCI-60 panel of tumor cell lines. Interestingly, the selected compounds displayed from modest to strong cytotoxic activities. Compound 3b demonstrated broad spectrum anti-tumor activity against the nine tumor sub-panels tested, while compound 3d proved to be lethal to most of the cancer cell lines as shown by their promising GI₅₀ and TGI values in NCI in vitro five dose testing. These results revealed that the synthesized compounds can potentially serve as leads for the development of novel chemotherapeutic agents and structure improvement will be necessary for some derivatives for enhancing their cellular activities and pharmacokinetic profile.

Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse

Although known for over 90 years, only in the past two decades has the chemistry of diboron(4) compounds been extensively explored. Many interesting structural features and reaction patterns have emerged, and more importantly, these compounds now feature prominently in both metal-catalyzed and metal-free methodologies for the formation of B-C bonds and other processes.

A direct and vicinal functionalization of the 1-methyl-2-quinolone framework: 4-alkoxylation and 3-chlorination

Bis(functionalization), 4-alkoxylation and 3-chlorination, of the 1-methyl-2-quinolone framework was achieved under mild conditions by a sequential treatment of 3-nitrated 1-methyl-2-quinolones with sodium alkoxide and N-chlorosuccinimide. Moreover, a succinimide group instead of an alkoxy group was introduced at the 4-position, affording a masked form of the 4-amino-3-chloro-2-quinolone derivative. Furthermore, the prepared vicinally functionalized quinolones thus obtained were subjected to a Suzuki-Miyaura coupling reaction, arylating the 3-position.

Convenient synthesis of organic-electronics-oriented building blocks via on-water and under-air homocoupling of (hetero)aryl iodides

An on-water homocoupling reaction is developed for the alternative synthesis of various organic-electronically versatile bi(hetero)aryls. These multi-function building blocks are indispensable to polymer chemistry and modern organic electronics.

Microwave-Assisted Transition-Metal-Catalyzed Synthesis of N-Shifted and Ring-Expanded Buflavine Analogues

Two novel and efficient strategies for the synthesis of hitherto unknown N-shifted and ring-expanded buflavine analogues are presented. Construction of the medium-sized ring system of the title molecules, a difficult task due to the high activation energy needed for the ring-closure with the additional rigidity imposed by the biaryl skeleton, was achieved by using Suzuki-Miyaura biaryl coupling and a ring-closing metathesis reaction as the key steps. The combination of a second-generation Grubbs catalyst and microwave irradiation proved to be highly useful in generating the otherwise difficult to obtain medium-sized ring system of the buflavine analogues.