Copper-Catalyzed Remote C−H Nitration of 8-Amidoquinolines

Chemo-and regioselective aqueous phase, co-acid free nitration of aromatics using traditional and nontraditional activation methods

Electrophilic aromatic nitrations are used for the preparation of a variety of synthetic products including dyes, agrochemicals, high energy materials, fine chemicals and pharmaceuticals. Traditional nitration methods use highly acidic and corrosive mixed acid systems which present a number of drawbacks. Aside from being hazardous and waste-producing, these methods also often result in poor yields, mostly due to low regioselectivity, and limited functional group tolerance. As a consequence, there is a need for effective and environmentally benign methods for electrophilic aromatic nitrations. In this work, the major aim was to develop reaction protocols that are more environmentally benign while also considering safety issues. The reactions were carried out in dilute aqueous nitric acid, and a broad range of experimental variables, such as acid concentration, temperature, time, and activation method, were investigated. Mesitylene and m-xylene were used as test substrates for the optimization. While the optimized reactions generally occurred at room temperature without any activation under additional solvent-free conditions, slight adjustments in acid concentration, stoichiometric equivalents, and volume were necessary for certain substrates, in addition to the activation. The substrate scope of the process was also investigated using both activated and deactivated aromatics. The concentration of the acid was lowered when possible to improve upon the safety of the process and avoid over-nitration. With some substrates we compared traditional and nontraditional activation methods such as ultrasonic irradiation, microwave and high pressure, respectively, to achieve satisfactory yields and improve upon the greenness of the reaction while maintaining short reaction times.

Palladium-Catalyzed C(sp3)-H Nitrooxylation of Aliphatic Carboxamides with Practical Oxidants

Here we report the palladium-catalyzed β-C(sp3)-H nitrooxylation of aliphatic carboxamides using a modified quinoline auxiliary. Notably, Al(NO3)3·9H2O was used as a nitrate source as well as a practical oxidant. The 5-chloro-8-aminoquinoline auxiliary was nitrated in situ during the reaction, which may enhance its directing ability and help its removal. The reaction has a broad substrate scope with a variety of aliphatic carboxamides. The multiple substituted auxiliary can be easily removed and recovered. Two C-H-insertion palladacycle intermediates were isolated and characterized to elucidate the mechanism.

Selective C3–H nitration of 2-sulfanilamidopyridines with tert-butyl nitrite

A selective C3–H nitration of bioactive 2-sulfanilamidopyridine derivatives, including corticosteroid 11-β-dehydrogenase isozyme, secretory phospholipase A2 inhibitor and human neutrophil elastase inhibitor, has been reported.

Diastereoselective [3 + 2] Cycloaddition of Quinoxalin-2(1H)-ones with Donor-Acceptor Cyclopropanes: Efficient Synthesis of Tetrahydro pyrrolo[1,2-a]quinoxalin-4(5H)-ones

A ytterbium triflate-catalyzed diastereoselective [3 + 2] cycloaddition of quinoxalinones with donor-acceptor cyclopropanes and cyclobutanes is described. A series of tetrahydropyrrolo-quinoxalinone derivatives were obtained in high yields (up to 96%) with excellent diastereoselectivities (up to 46:1). Other medicinally important heterocycles like benzoxazinone, isoquinoxalinone, and dibenzoxazepine derivatives were also suitable for the desired annulation reaction. The current method is applicable for the scale-up reaction. Further, the utility of this annulation reaction is demonstrated by the synthesis of densely functionalized proline derivatives.

Pd-Catalyzed C-H Halogenation of Indolines and Tetrahydroquinolines with Removable Directing Group

Pd-catalyzed directing-group-assisted regioselective halogenations to C7 of indolines and C8 of tetrahydroquinolines were achieved in good to excellent yields. The practicality and utility of the developed method have been illustrated by various functional group transformations such as arylation, alkenylation, cyanation, and silylation utilizing the installed synthetic handle. The concise synthesis of primaquine, an antimalarial drug, and formal syntheses of two bioactive natural products, hippadine and pratosine, have also been demonstrated.

Cu(II)-Catalyzed Ortho C(sp2)-H Diarylamination of Arylamines To Synthesize Triarylamines

A copper-catalyzed, directed ortho C-H diarylamination of indoles, indolines, anilines, and N-aryl-7-azaindoles has been established. Only copper salt as the catalyst and oxygen as the terminal oxidant are used to synthesize triarylamines using various diarylamines including carbazole and phenothiazine. Mechanistic interrogation reveals that copper plays a dual role.

Recent advances in transition metal-catalyzed C(sp2)–H nitration

This review updates advances of direct C(sp²)–H nitration for the synthesis of nitroaromatic compounds and the mechanisms during the past decade.

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.

Ruthenium(ii)-catalyzed remote C–H addition of 8 aminoquinoline amide to activated aldehyde

Remote C–H addition of 8-aminoquinoline amides at C-5 position to activated aldehydes have been developed using Ru(ii)-catalyst.

Iron promoted C3–H nitration of 2H-indazole: direct access to 3-nitro-2H-indazoles

An efficient C3–H functionalization of indazole has been demonstrated. Notably, this method involves chelation-free radical C–H nitration on 2H-indazole. The radical mechanism was confirmed by control experiments and quantum chemical calculations. The synthetic utility has been proven by the synthesis of bio-relevant benzimidazoindazoles via reductive cyclization.

Copper-mediated domino C–H iodination and nitration of indoles

An efficient and cost-effective copper-mediated aerobic oxidative C–H iodination and nitration of indoles via double C–H functionalization is reported. The domino process proceeds smoothly under mild aerobic conditions to give 3-iodo-2-nitroindoles in one step with high regioselectivity and a broad substrate scope.

Remote alkylation of N-(quinolin-8-yl)benzamides with alkyl bromides via ruthenium(ii)-catalyzed C–H bond activation

A ruthenium(ii) catalyzed remote C-5 alkylation of the quinoline ring of N-(quinolin-8-yl)benzamides with alkyl bromides via C–H bond activation is described.