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

Ru(II)-Catalyzed C7 Trifluoromethylthiolation and Thioarylation of Indolines Using Bench-Stable Reagents

A Ru(II)-catalyzed C(sp2)-H trifluoromethylthiolation and thioarylation of indolines using bench-stable reagents have been explored. Diversely substituted indolines were functionalized at C7 position in good to excellent yields. Radical quenching, deuterium labeling, KIE, and reaction order determination experiments were performed to support the proposed reaction pathway. Gram-scale synthesis and post-transformation of the synthesized products have also been carried out to demonstrate the applicability of the developed catalytic protocol.

Ru(II)-Catalyzed Sustainable C-H Methylation of Indolines with Organoboranes in Ethanol

A sustainable protocol for Ru(II)-catalyzed regioselective C(sp2)-H methylation of indolines in the presence of ethanol has been explored. A wide array of substituted indolines were successfully methylated via the developed protocol with good to excellent yields. Deuterium labeling experiments suggested the reversible nature of the C-H activation step. Kinetic isotope effect studies revealed that C-H activation might be the rate-determining step. Gram scale reaction and post-transformation reactions of the methylated product demonstrated the potential of the developed protocol.

Cobalt(III)-Catalyzed Directed C-7 Selective C-H Alkynylation of Indolines with Bromoalkynes

A cobalt(III)-catalyzed directed C-7 alkynylation of indolines with easily accessible bromoalkynes has been developed. The reaction has a broad substrate scope with excellent yields and represents a powerful route to the synthesis of 7-alkynyl-substituted indolines. In addition, the reaction can be extended to the coupling of N-aryl 7-azaindoles, highlighting the synthetic practicability of the strategy.

Synthesis of C4-Aminated Carbazoles and Their Derivatives via Pd/NBE Chemistry

Carbazole, as one of the most important organic frameworks, has been used in optoelectronic materials and biochemistry. However, the synthesis of C4-substituted carbazole has always been an unsolved problem. This report describes the one-step synthesis of C4-aminated carbazoles and their derivatives through the series reaction of C-H amination and arylation. The substrate scope is wide. C4-Amino carbazoles substituted by C2, C6, C7, and C8 methyl groups, especially carbazole derivatives of fused rings, pyridine, and dibenzofuran, can be synthesized.

Copper-catalyzed regioselective C2-H chlorination of indoles with para-toluenesulfonyl chloride

A copper-catalyzed, pyrimidine directed regioselective C-H chlorination of indoles with para-toluenesulfonyl chloride (TsCl) has been developed. The reactions proceeded smoothly in the presence of 20 mol% of Cu(OAc)₂ as the catalyst and TsCl as the chlorine source, delivering C2-chlorinated indoles with structural diversity in moderate to excellent yields. Mechanistic studies suggested that single electron transfer (SET) from Cu(II) to TsCl accompanied by the release of the p-toluenesulfonyl radical and the related Cu(III)Cl species might be involved in the reactions.

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.

Predictable site-selective functionalization: Promoter group assisted para-halogenation of N-substituted heteroaromatics under metal-free condition

Herein, regioselective para-C-H halogenation of N-pyrimidyl (hetero)aromatics through S_EAr (electrophilic aromatic substitution) type reaction is disclosed. S_EAr type reaction has been utilized for the C5-bromination of indolines (para-selective) with N-bromosuccinimide under metal and additive-free conditions in good to excellent yields. The developed methodology is also applicable for iodination and challenging chlorination. The pyrimidyl group is identified as a reactivity tuner that also controls the regioselectivity. The present method is also applicable for selective halogenation of aniline, pyridine, indole, oxindole, pyrazole, tetrahydroquinoline, isoquinoline, and carbazole. DFT studies such as Fukui nucleophilicity and natural charge maps also support the observed p-selectivity. Post-functionalization of the title compound into the corresponding arylated, olefinated, and dihalogenated products is achieved in a one-pot, two-step fashion. Late-stage C-H bromination was also executed on drug/natural molecules (harmine, etoricoxib, clonidine, and chlorzoxazone) to demonstrate the applicability of the developed protocol.

Transient Directing Group Strategy as a Unified Method for Site Selective Direct C4-H Halogenation of Indoles

A unified method for direct C4-H halogenation of indoles has been accomplished with the assistance of anthranilic acids as suitable transient directing groups. Exclusive site selectivity (one out of five potential reactive sites) as well as good functional group tolerance was obtained to install three kinds of halogen atoms (Cl, Br and I, respectively) by using inexpensive N-halosuccinimides (NXS) as halogen sources under mild conditions. Taking advantage of the rich functional groups in the product, a diversity of nitrogen-containing heterocycles were facily constructed via one-step late-stage derivations.

Cu(II)-Catalyzed C-N, C-O, C-Cl, C-S, and C-Se Bond Formation via C(sp2)-H Activation Using 7-Azaindole as an Intrinsic Directing Group

A general protocol has been developed for the construction of carbon-heteroatom (C-N, C-Cl, C-O, C-S, and C-Se) bonds using the bench stable, earth-abundant, and environmentally benign copper catalyst. Only oxygen is sufficient to regenerate the copper catalyst. Control experiments suggested that the proto-demetalation step is reversible. Depending on the coupling partner, the reaction follows either disproportionation or radical pathways to complete the catalytic cycle. The synthetic utility of the developed protocol has been demonstrated via various functional group transformations.

Synthesis of chiral branched allylamines through dual photoredox/nickel catalysis

Allylamines are versatile building blocks in the synthesis of various naturally occurring products and pharmaceuticals. In contrast to terminal allylamines, the methods of synthesis of their branched congeners with internal, stereodefined double bonds are less explored. This work describes a new approach for the preparation of allylamines via cross-coupling of alkyl bromides with simple 3-bromoallylamines by merging the photoredox approach and Ni catalysis. The reaction proceeds under mild conditions, under blue light irradiation, and in the presence of an organic dye, 4CzIPN, as a photocatalyst. The scope of suitable reaction partners is broad, including alkyl bromides bearing reactive functionalities (e.g., esters, nitriles, aldehydes, ketones, epoxides) and N-protected allylamines, as well as N-allylated secondary and tertiary amines and heterocycles. The employment of non-racemic starting materials allows for rapid and easy construction of complex multifunctional allylamine derivatives without the loss of enantiomeric purity.

Iron-Mediated Selective Sulfonylmethylation of Aniline Derivatives with p-Toluenesulfonylmethyl Isocyanide (TosMIC)

An iron-mediated highly selective C-H sulfonylmethylation of aniline derivatives with p-toluenesulfonylmethyl isocyanide in a mixture solvent of H₂O and PEG₄₀₀ under an Ar atmosphere has been realized. This transformation proceeds with operational convenience, use of earth-abundant metal catalyst and nontoxic media, broad substrate scope, and good functional group tolerance. The current methodology could be applied to the regioselective C-H sulfonylmethylation of indolines, tetrahydroquinolines, and tertiary anilines.

Ruthenium-Catalyzed Electrochemical Synthesis of Indolines through Dehydrogenative [3 + 2] Annulation with H2 Evolution

A dehydrogenative [3 + 2] annulation reaction of aniline derivatives and alkenes has been developed via the ruthenium-electron catalytic systems for the synthesis of versatile indolines. Electricity is used as a sustainable oxidant to regenerate the active Ru(II) catalyst and promote H₂ evolution. This protocol is ecofriendly and easy to handle as it uses a simple undivided cell in mild conditions without the employment of metal oxidants.