Quinoline N-oxides Research Articles

Synthesis of 3-(2-quinolyl) chromones from ynones and quinoline N-oxides via tandem reactions under transition metal- and additive-free conditions.

A novel method for the synthesis of 3-(2-quinolyl) chromones through a tandem [3+2] cycloaddition/ring-opening/O-arylation from ynones and quinoline N-oxides has been developed. This protocol proceeds under transition metal- and additive-free conditions and can be amplified to the gram level in 91% yield. 3-(1-Isoquinolyl) and 3-(2-pyridyl) chromones are also successfully synthesized using isoquinoline and pyridine N-oxides under basic conditions. Various heteroarene-contaning chromones were afforded in 30-98% yields, which are difficult to be obtained and are compounds of interest in pharmaceutical chemistry and chemical biology.

Recent Progress in the Functionalization of Quinoline N-Oxide

Recent Progress in the Functionalization of Quinoline <i>N</i>-Oxide

Regioselective Arylation of Quinoline N-Oxides (C8), Indolines (C7) and N-tert-Butylbenzamide with Arylboronic Acids.

Herein, we disclose Ru(II)-catalyzed regioselective distal C(sp2)–H arylation of quinoline N-oxide with arylboronic acids to 8-arylquinolines. In the developed method, the Ru(II)-catalyst shows dual activity, that is, distal C–H activation of quinoline N-oxides followed by in situ deoxygenation of arylated quinoline N-oxide in the same pot. The current catalytic method features use of Ru metal as the catalyst and arylboronic acids as the arylating source under mild reaction conditions. Use of the Rh(III)-catalyst in place of Ru(II) under the same conditions afforded 8-arylquinoline N-oxides with excellent regioselectivity. Furthermore, the developed Ru(II) catalytic system is also extended for the C(sp2)–H arylation of indolines, N-tert-butylbenzamide, and 6-(5H)-phenanthridinone. Formation of the quinoline N-oxide coordinated ruthenium adduct is found to be the key reaction intermediate, which has been characterized by single crystal X-ray diffraction and NMR spectroscopy.

Metal-Free Synthesis of 3-(Iso)quinolinyl 4-Chromenones and 3-(Iso)quinolinyl 4-Quinolones from (Iso)quinoline N-Oxides and Ynones.

A general approach for the synthesis of 3-(iso)quinolinyl 4-chromenones and 3-(iso)quinolinyl 4-quinolones from (iso)quinoline N-oxides and ynones under metal-free conditions was developed. The reaction of (iso)quinoline N-oxide with the electron-deficient alkyne first generated an (iso)quinolinyl β-diketone intermediate, which then underwent an intramolecular dehydration, affording 3-(iso)quinolinyl 4-chromenones and 3-(iso)quinolinyl 4-quinolones.

Rh(III)-catalyzed C8 arylation of quinoline N-oxides with arylboronic acids

Herein, we report the first RhIII-catalyzed regioselective C8 arylation of quinoline N-oxides with commercially available arylboronic acids as coupling partners. This procedure is simple, and the reaction shows perfect regioselectivity, a broad substrate scope, and isolated yields of up to 92%. We demonstrate the utility of the reaction by using it for late-stage functionalization of a fungicide.

Visible-Light-Promoted C2 Trifluoromethylation of Quinoline N-Oxides

A photoredox catalytic strategy has been described for the direct C2 trifluoromethylation of quinoline N-oxides. This reaction is compatible with a range of synthetically relevant functional groups for providing efficient synthesis of a variety of C2 trifluoromethyl quinoline N-oxides at room temperature. Mechanistic studies indicated that the reaction proceeds via a radical pathway.

Visible-light-induced deoxygenative C2-sulfonylation of quinoline N-oxides with sulfinic acids for the synthesis of 2-sulfonylquinoline via radical reactions

A simple and efficient method for the synthesis of 2-sulfonylquinoline from deoxygenative C2-sulfonylation of quinoline N -oxides with sulfinic acid induced by visible light is presented. This protocol shows a broad substrate scope, and desired products with various substituents can be formed in moderate to high yields at room temperature. A simple and efficient method for the synthesis of 2-sulfonylquinoline from deoxygenative C2-sulfonylation of quinoline N -oxides with sulfinic acid induced by visible light is presented. This protocol shows a broad substrate scope, and desired products with various substituents can be formed in moderate to high yields at room temperature.

TsCl-promoted sulfonylation of quinoline N-oxides with sodium sulfinates in water

An eco-friendly protocol for the synthesis of various 2-sulfonyl quinolines/pyridines through sulfonylation of heteroaromatic N-oxides with sodium sulfinates in water at ambient temperature under metal- and oxidant-free conditions has been developed. The mild reaction conditions, high reaction efficiency, operational simplicity, short reaction time and remarkable functional-group compatibility make the developed protocol very attractive for the preparation of 2-sulfonyl N-heteroaromatic compounds.

Ru-Catalyzed Deoxygenative Regioselective C8-H Arylation of Quinoline N-Oxides.

Regioselective C-H functionalization on quinolines is of high interest to lead to value-added products. Herein, we describe the development of Ru-catalyzed deoxygenative regioselective C8 arylation of quinoline N-oxides with arylboronic esters. Mechanistic studies revealed that it proceeds in a tandem process of arylation and then deoxygenation, wherein both steps were found to be catalytic with the ruthenium species.

Rh(III)-Catalyzed C(8)-H Activation of Quinoline N-Oxides: Regioselective C-Br and C-N Bond Formation.

A highly efficient and regioselective Rh(III)-catalyzed protocol for C8-bromination and amidation of quinoline N-oxide was developed. The transformation was found to be successful up to gram scale with excellent functional group tolerance and wide substrate scope. The mechanistic study revealed five-membered rhodacycle with quinoline N-oxide as a key intermediate for regioselective C8-functionalization. In addition, NFSI (N-fluorobis(phenylsulfonyl)-imide) was explored as an amidating reagent for C8-amidation of quinoline N-oxide for the first time.

Copper-Catalyzed Deoxygenative C2-Sulfonylation of Quinoline N-Oxides with DABSO and Phenyldiazonium Tetrafluoroborates for the Synthesis of 2-Sulfonylquinolines via a Radical Reaction

An efficient and practical method for the synthesis of 2-sulfonylquinolines through copper-catalyzed deoxygenative C2-sulfonylation of quinoline N-oxides with 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) (DABSO) and phenyldiazonium tetrafluoroborates is demonstrated. Products with various substituents were obtained in moderate to high yields.

Catalyst-Free Synthesis of 2-Anilinoquinolines and 3-Hydroxyquinolines via Three-Component Reaction of Quinoline N-Oxides, Aryldiazonium Salts, and Acetonitrile.

A rapid microwave-assisted, catalyst-free, three-component synthesis of various 2-anilinoquinolines from quinoline N-oxides and aryldiazonium salts in acetonitrile under microwave irradiation is reported. This reaction utilizes acetonitrile as a single nitrogen source and involves the formation of two new C-N bonds via the formal [3 + 2] cycloaddition reaction. In the case of 2-substituted quinolines, 3-hydroxyquinoline was observed as the main product via a 1,3 shift of the oxygen atom from N-oxide to the C3 position of quinolines.

Gold-Catalyzed Oxidative Hydrative Alkenylations of Propargyl Aryl Thioethers with Quinoline N-Oxides Involving a 1,3-Sulfur Migration.

This work reports gold-catalyzed oxidative alkenylations of quinoline N-oxides with propargyl aryl thioethers to afford 3-hydroxy-1-alkylidenephenylthiopropan-2-one via a 1,3-sulfur group migration. The mechanism of this reaction is postulated to involve an α-oxo gold carbene intermediate followed by formation of a four-membered sulfonium ring that is ring-opened by one H2O to form a gold enolate. A final condensation of this enolate with a second quinoline N-oxide delivers an alkenylation product accompanied by a 1,3-sulfur shift.

RhIII -Catalyzed Straightforward Synthesis of Benzophenanthroline and Benzophenanthrolinone Derivatives using Anthranils.

An efficient pot-economic and step-economic RhIII -catalyzed site-selective direct amination/annulation strategy was developed for the synthesis of benzophenanthroline derivatives using quinoline N-oxides and anthranils. The method was further extended to the synthesis of nitrogen-containing extended π-conjugated benzophenanthrolinone derivatives. Late-stage functionalizations of cinchonidine and cinchophen derivatives and synthesis of a bioactive quinolino-indole were achieved.

Rh/O2-Catalyzed C8 Olefination of Quinoline N-Oxides with Activated and Unactivated Olefins.

The rhodium/O2 system-catalyzed distal C(sp2)-H olefination of quinoline N-oxides is developed. Molecular oxygen has been explored as an economic and clean oxidant, an alternative to inorganic oxidants. A wide substrate scope with respect to quinoline N-oxides and olefins (activated acrylates and styrenes; unactivated aliphatic olefins) demonstrates the robustness of the developed catalytic method. Interestingly, 2-substituted quinoline N-oxides also afforded good yields of the corresponding C8-olefinated products. Kinetic isotope studies and deuterium-labeling experiments have been performed to understand the preliminary mechanistic pathway. The applicability of the developed method is demonstrated by utilizing natural product-derived substrates and by converting the C8-olefinated quinoline N-oxides into various other useful molecules.

Simple and scalable electrochemical synthesis of 2,1-benzisoxazoles and quinoline N-oxides.

Cathodic reduction of the nitro moiety and subsequent intramolecular cyclization affords different substituted 2,1-benzisoxazoles and quinoline N-oxides. This methodology allows the synthesis of two different types of heterocycles from common simple starting materials, using electrons as a sole reagent for this transformation. The electrolysis can be conducted in a very simple undivided electrolysis cell under constant current conditions. This permits working on a larger scale compared to other electrochemical methodologies and represents a significant advantage.

Direct synthesis of 8-acylated quinoline N-oxidesviapalladium-catalyzed selective C–H activation and C(sp2)–C(sp2) cleavage

An efficient method for the synthesis of 8-acylated quinoline N-oxides from the reaction of quinoline N-oxides with α-diketonesviaC–C bond cleavage was developed. A variety of quinoline N-oxides and α-diketones with different groups was well tolerated in this system.

Visible-light-induced deoxygenative C2-sulfonylation of quinoline N-oxides with sulfinic acids

The first example of direct synthesis of 2-sulfonylquinolines through visible-light-induced deoxygenative C2-sulfonylation of quinoline N-oxides with organic dye as the catalyst and ambient air as the sole oxidant was developed.

Exogenous-oxidant- and catalyst-free electrochemical deoxygenative C2 sulfonylation of quinoline N-oxides.

An exogenous-oxidant- and catalyst-free electrochemical deoxygenative C2 sulfonylation reaction has been achieved. By employing quinoline N-oxides as the starting materials, the electrochemical C-H sulfonylation of electron-deficient quinolines was indirectly achieved at room temperature and a variety of sulfonylated quinoline derivatives were synthesized in modest to high yield with excellent regioselectivity. Notably, this protocol is the first example for synthesizing sulfonylated electron-deficient heteroarenes/arenes through electrochemistry.

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.