An efficient one pot transfer hydrogenation and N-alkylation of quinolines with alcohols mediated by Pd/C/Zn

A Pd/C/Zn mixture with alcohols has been revealed to be an efficient transfer hydrogenation system to quinolines. Furthermore, the metals mixture is able to activate alcohols as N-alkylating agents in a hydrogen autotransfer process. 1,2,3,4-Tetrahydroquinolines and N-alkylated tetrahydroquinolines from quinolines have been obtained with excellent yields in one step.     

A Simple Iridicycle Catalyst for Efficient Transfer Hydrogenation of N‐Heterocycles in Water

A cyclometalated iridium complex is shown to catalyse the transfer hydrogenation of various nitrogen heterocycles, including but not limited to quinolines, isoquinolines, indoles and pyridinium salts, in an aqueous solution of HCO₂H/HCO₂Na under mild conditions. The catalyst shows excellent functional‐group compatibility and high turnover number (up to 7500), with catalyst loadings as low as 0.01 mol % being feasible. Mechanistic investigation of the quinoline reduction suggests that the transfer hydrogenation proceeds via both 1,2‐ and 1,4‐addition pathways, with the catalytic turnover being limited by the step of hydride transfer.     

Iridium-catalyzed asymmetric transfer hydrogenation of quinolines with Hantzsch esters

The iridium-catalyzed enantioselective transfer hydrogenation of quinolines with Hantzsch esters was developed with up to 88% ee using [Ir(COD)Cl]₂/(S)-SegPhos/I₂ as a catalyst.     

Cyclopentadiene-based Brønsted acid as a new generation of organocatalyst for transfer hydrogenation of 2-substituted quinoline derivatives

A simple and readily available cyclopentadiene-based Brønsted acid was employed to catalyze the transfer hydrogenation of 2-substituted quinolines using Hantzsch ester as the hydrogen source. This conceptually new designed organocatalyst demonstrates remarkably high efficiency for this transformation and a variety of substituted 1,2,3,4-tetrahydroquinoline derivatives were afforded in excellent yields under mild reaction conditions.     

Multifunctional Catalysis of Heteropoly Acid: One‐Pot Synthesis of Quinolines from Nitroarene and Various Aldehydes in the Presence of Hydrazine

12‐Molybdophosphoric acid catalyzed transfer hydrogenation of nitroarene by hydrazine in a homogeneous phase. This catalytic system was applicable to one‐pot quinolines synthesis in the presence of various aldehydes in water. This method provides a new and efficient protocol in terms of mild reaction conditions, clean reaction profiles, small quantity of catalyst, and simple work‐up procedure.     

High efficient iron-catalyzed transfer hydrogenation of quinolines with Hantzsch ester as hydrogen source under mild conditions

A highly efficient transfer hydrogenation of quinolines with Hantzsch ester as hydrogen source in the presence of 1 mol% Fe(OTf)₂ under mild conditions has been developed. A series of substituted 1,2,3,4-tetrahydroquinoline derivatives were afforded in excellent yields with good functional group tolerance.     

Dihydrophenanthridine: a new and easily regenerable NAD(P)H model for biomimetic asymmetric hydrogenation

A new and easily regenerable NAD(P)H model 9,10-dihydrophenanthridine (DHPD) has been designed for biomimetic asymmetric hydrogenation of imines and aromatic compounds. This reaction features the use of hydrogen gas as terminal reductant for the regeneration of the DHPD under the mild condition. Therefore, the substrate scope is not limited in benzoxazinones; the biomimetic asymmetric hydrogenation of benzoxazines, quinoxalines, and quinolines also gives excellent activities and enantioselectivities. Meanwhile, an unexpected reversal of enantioselectivity was observed between the reactions promoted by the different NAD(P)H models, which is ascribed to the different hydride transfer pathway.     

Asymmetric transfer hydrogenation of quinolines using tethered Ru(II) catalysts

The first report of an asymmetric transfer hydrogenation, in formic acid/triethylamine, of quinolines is described. Using a Ru(II) catalyst containing a 4-carbon tether, products of up to 73% ee were formed, whilst a Rh(III)-tethered catalyst gave products of up to 94% ee.     

芳香硝基化合物原位液相加氢一锅法合成喹啉类化合物

以芳香硝基化合物为起始原料,以2%Pt-Sn/γ-Al2O3为催化剂,采用原位液相加氢法可以一锅法合成喹啉类化合物,考察了Pt/Sn摩尔比、反应温度、原料浓度和水含量等对反应性能的影响.结果表明,在Pt/Sn摩尔比0.5,220oC,5.0MPa,原料浓度6%,水含量30%及反应物停留时间为72s的条件下,生成产物6-甲氧基-2-甲基喹啉的收率可达72%.     

Catalytic asymmetric hydrogenation of α-ketoesters and quinoline using electronically enriched BINAP

Electronically enriched chiral BINAP derivatives were synthesized incorporating electron-donating substituents at the para-phenyl position and evaluated for the Ru-catalyzed homogeneous asymmetric hydrogenation of α-ketoesters with up to 92% ee. These diphophosphines were also excellent ligands for the iridium-catalyzed asymmetric hydrogenation of quinolines.     

Simple manganese carbonyl catalyzed hydrogenation of quinolines and imines

Manganese-catalyzed hydrogenation of unsaturated molecules has made tremendous progresses recently benefiting from non-innocent pincer or bidentate ligands for manganese. Herein, we describe the hydrogenation of quinolines and imines catalyzed by simple manganese carbonyls, Mn₂(CO)₁₀ or MnBr(CO)₅, thus eliminating the prerequisite pincer-type or bidentate ligands.     

Quinoline and 2-nitroimino-1, 3-diazacycloalkane hybrids: Design,synthesis and insecticidal activity

A library of new hybrid molecules comprising quinoline, 2-nitroimino-1, 3-diazacycloalkane motifs were designed and synthesized as plausible neonicotinoid analogues. These compounds were synthesized from 2-chloro/aryloxy-3-formyl quinolines and guanidine nitrate with the coupling of 2-chloro/aryloxy-3-(chloromethyl)quinolines, 2-nitroimino-1, 3-diazacycloalkanes under phase transfer catalysis (PTC) as crucial step. All the compounds were obtained in excellent yields (80–90%) and were characterized by ¹H, ¹³C NMR and mass spectrometry. The newly generated compounds were screened for insecticidal activity against aphids in safflower field and some of them displayed moderate activity.     

Asymmetric hydrogenation of quinolines activated by Brønsted acids

Enantioselective hydrogenation of quinolines and quinoxalines catalyzed by iridium/diphosphine complex with catalytic amount of Brønsted acid as activator was developed. In the presence of piperidine·TfOH as the activator, full conversions and up to 92% ee were obtained.     

New class of P-stereogenic chiral Brønsted acid catalysts derived from chiral phosphinamides

A new class of NH Brønsted acid organocatalysts that feature P-stereogenic chirality was developed. These catalysts were prepared from P-stereogenic chiral phosphinamides and show similar reactivity to BINOL derived phosphoric acid toward the reduction of quinolines via transfer hydrogenation. It shows that stereoselectivity is induced by the P-chiral environment that is created by the substituents attached to the phosphorous atom, which can be readily tuned and modified.     

Asymmetric hydrogenation of quinolines catalyzed by iridium complexes of BINOL-derived diphosphonites

A chiral diphosphonite, derived from BINOL and with an achiral diphenyl ether backbone, is an excellent ligand for the Ir-catalyzed asymmetric hydrogenation of quinolines; achiral P-ligands serving as possible additives (ee = 73-96%).     

Synthesis of new chiral 2-functionalized-1,2,3,4-tetrahydroquinoline derivatives via asymmetric hydrogenation of substituted quinolines

The asymmetric hydrogenation of a series of quinolines substituted by a variety of functionalized groups linked to the C2 carbon atom is providing access to optically enriched 2-functionalized 1,2,3,4-tetrahydroquinolines in the presence of in situ generated catalysts from [Ir(cod)Cl]₂, a bisphosphine, and iodine. The enantioselectivity levels were as high as 96% ee.     

Biomimetic Hydrogenation Catalyzed by a Manganese Model of [Fe]-Hydrogenase

[Fe]-hydrogenase is an efficient biological hydrogenation catalyst. Despite intense research, Fe complexes mimicking the active site of [Fe]-hydrogenase have not achieved turnovers in hydrogenation reactions. Herein, we describe the design and development of a manganese(I) mimic of [Fe]-hydrogenase. This complex exhibits the highest activity and broadest scope in catalytic hydrogenation among known mimics. Thanks to its biomimetic nature, the complex exhibits unique activity in the hydrogenation of compounds analogous to methenyl-H₄MPT⁺, the natural substrate of [Fe]-hydrogenase. This activity enables asymmetric relay hydrogenation of benzoxazinones and benzoxazines, involving the hydrogenation of a chiral hydride transfer agent using our catalyst coupled to Lewis acid-catalyzed hydride transfer from this agent to the substrates.     

4-hydroxy-2-quinolones. 124. Synthesis and structure of ethyl 2-bromomethyl-5-oxo-1,2,6,7,8,9-hexahydro-5H-oxazolo-[3,2-<Emphasis Type="Italic">a</Emphasis>]quinoline-4-carboxylate

The hydrogenation of the benzene part of the molecule in N-allyl-substituted 4-hydroxy-2-quinolinones does not affect the nature of their bromination by molecular bromine and gives 2-bromomethyl-5-oxo-1,2,6,7,8,9-hexahydro-5H-oxazolo[3,2-a]quinolines. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1180–1188, August, 2007.     

Biomimetic Hydrogenation Catalyzed by a Manganese Model of [Fe]‐Hydrogenase

[Fe]‐hydrogenase is an efficient biological hydrogenation catalyst. Despite intense research, Fe complexes mimicking the active site of [Fe]‐hydrogenase have not achieved turnovers in hydrogenation reactions. Herein, we describe the design and development of a manganese(I) mimic of [Fe]‐hydrogenase. This complex exhibits the highest activity and broadest scope in catalytic hydrogenation among known mimics. Thanks to its biomimetic nature, the complex exhibits unique activity in the hydrogenation of compounds analogous to methenyl‐H₄MPT⁺, the natural substrate of [Fe]‐hydrogenase. This activity enables asymmetric relay hydrogenation of benzoxazinones and benzoxazines, involving the hydrogenation of a chiral hydride transfer agent using our catalyst coupled to Lewis acid‐catalyzed hydride transfer from this agent to the substrates.     

Iridium-catalyzed hydrogenation of N-heterocyclic compounds under mild conditions by an outer-sphere pathway

A new homogeneous iridium catalyst gives hydrogenation of quinolines under unprecedentedly mild conditions-as low as 1 atm of H(2) and 25 °C. We report air- and moisture-stable iridium(I) NHC catalyst precursors that are active for reduction of a wide variety of quinolines having functionalities at the 2-, 6-, and 8- positions. A combined experimental and theoretical study has elucidated the mechanism of this reaction. DFT studies on a model Ir complex show that a conventional inner-sphere mechanism is disfavored relative to an unusual stepwise outer-sphere mechanism involving sequential proton and hydride transfer. All intermediates in this proposed mechanism have been isolated or spectroscopically characterized, including two new iridium(III) hydrides and a notable cationic iridium(III) dihydrogen dihydride complex. DFT calculations on full systems establish the coordination geometry of these iridium hydrides, while stoichiometric and catalytic experiments with the isolated complexes provide evidence for the mechanistic proposal. The proposed mechanism explains why the catalytic reaction is slower for unhindered substrates and why small changes in the ligand set drastically alter catalyst activity.