Regioselective synthesis of 6-nitroindole derivatives from enaminones and nitroaromatic compounds via transition metal-free C-C and C-N bond formation

Few methods are known for the synthesis of nitroindole derivatives. A simple and practical Cs₂CO₃-promoted method for the synthesis of 6-nitroindole derivatives from enaminones and nitroaromatic compounds has been developed. Two new C-C and C-N bonds were formed in a highly regioselective manner under transition metal-free conditions.

Synthesis of 1H-Indazoles via Silver(I)-Mediated Intramolecular Oxidative C-H Bond Amination

We described a silver(I)-mediated intramolecular oxidative C-H amination that enables the construction of assorted 1H-indazoles that are widely applicable in medicinal chemistry. The developed amination was found to be efficient for the synthesis of a variety of 3-substituted indazoles that are otherwise difficult to be synthesized by other means of C-H aminations. Preliminary mechanistic studies suggested that the current amination proceeds via single electron transfer (SET) mediated by Ag(I) oxidant.

Investigation of the intramolecular hydrogen bonding interactions and excited state proton transfer mechanism for both Br-BTN and CN-BTN systems

In the present work, two novel Br-BTN and CN-BTN compounds have been investigated theoretically. We in-depth explore the excited state hydrogen bonding interactions and the excited state intramolecular proton transfer (ESIPT) behaviors for the Br-BTN and CN-BTN system. We firstly verify the formation of hydrogen bond effects of O-H⋯N based on reduced density gradient (RDG) versus sign(λ 2)ρ. The simulated primary bond lengths and bond angles as well as infrared (IR) vibrational spectra reveal that the hydrogen bond O-H⋯N should be strengthened in the excited state. Combining the frontier molecular orbital (MO) investigations, we infer that the charge transfer phenomenon (from HOMO to LUMO) around hydrogen bonding moieties reveals the tendency of ESIPT reaction. Particularly, the increased electronic densities around proton acceptor atoms facilitate attracting a hydrogen proton, which plays a decisive role in opening the ESIPT reaction. Via constructing potential energy curves in both S0 and S1 states, the ultrafast ESIPT process can be verified which explains previous experimental characteristics. Furthermore, via searching the transition state (TS) structure and constructing the intrinsic reaction coordinate (IRC) reaction path, we check and confirm the ESIPT mechanism for both Br-BTN and CN-BTN systems. We sincerely hope that our theoretical work could guide novel applications based on Br-BTN and CN-BTN compounds in future.

Crystal structure, DFT calculations and Hirshfeld surface analysis of 3-(4-methyl-phen-yl)-6-nitro-1H-indazole

The asymmetric unit of the title compound, C14H11N3O3, consists of two independent mol-ecules having very similar conformations in which the indazole moieties are planar. The independent mol-ecules are distinguished by small differences in the rotational orientations of the nitro groups. In the crystal, N-H⋯O and C-H⋯O hydrogen bonds form zigzag chains along the b-axis direction. Additional C-H⋯O hydrogen bonds link the chains into layers parallel to (10). These are connected by slipped π-stacking and C-H⋯π(ring) inter-actions.

A Redox-Active Cascade Precursor: Isolation of a Zwitterionic Triphenylphosphonio-Hydrazyl Radical and an Indazolo-Indazole Derivative

A redox-active [ML] unit (M = Co^II and Mn^II; LH₂ = N'-(1,4-dioxo-1,4-dihydronaphthalen-2-yl)benzohydrazide) defined as a cascade precursor that undergoes a multicomponent redox reaction comprising of a C-N bond formation, tautomerization, oxidation, C-C coupling, demetalation, and affording 6,14-dibenzoylbenzo[f]benzo[5,6]indazolo[3a,3-c]indazole-5,8,13,16-tetraone (^IndL₂) is reported. Conversion of LH₂ → ^IndL₂ in air is overall a (6H⁺+6e) oxidation reaction, and it opens a route for the syntheses of bioactive diarylindazolo[3a,3-c]indazole derivatives. The reaction occurs via a radical coupling reaction, and the radical intermediate was isolated as a triphenylphosphonio adduct. In presence of PPh₃ the [ML] unit promotes a reaction that involves a C-P bond formation, tautomerization, and oxidation to yield a stable zwitterionic triphenylphosphonio-hydrazyl radical (^PPh3L^±•). Conversion of LH₂ → ^PPh3L^±• is a (3H⁺+3e) oxidation reaction. To authenticate the [ML] unit, in addition to the ^IndL₂, a zinc(II) complex, [(L₃)Zn^II(H₂O)Cl]·2MeOH (1·2MeOH), was successfully isolated (L₃H = a pyridazine derivative of 1,4 naphthoquinone) from a reaction of LH₂ with hydrated ZnCl₂. Conversion of 3LH₂ → 1 is also a multicomponent (6H⁺+6e) oxidation reaction promoted by zinc(II) ion via a radical intermediate. Facile oxidation of [L^2-] to [L^•-] that was considered as an intermediate of these conversions was confirmed by isolating a 1,4 naphthoquinone-benzhydrazyl radical (LH^•) complex, [(LH^•)Zn^II(H₂O)Cl₂] (2H^•). The intermediates of LH₂ → ^IndL₂, LH₂ → ^PPh3L^±•, and 3LH₂ → 1 conversions were analyzed by electrospray ionization mass spectroscopy. The molecular and electronic structures of ^PPh3L^±•, ^IndL₂, 1·2MeOH, and 2H^• were confirmed by single-crystal X-ray crystallography, electron paramagnetic resonance spectroscopy, and density functional theory calculations.

N-Tosylhydrazones: versatile synthons in the construction of cyclic compounds

N-Tosylhydrazones have been extensively explored as versatile building blocks in the construction of various cyclic compounds.

Transition Metal-Participated Synthesis and Utilization of N-containing Heterocycles: Exploring for Nitrogen Sources

This account aims to describe our recent efforts on the synthesis and utilization of N-containing heterocycles, where transition metals participate in the synthesis. A variety of nitrogen sources, including amines, amides, hydrazones, pyrimidines, isocyanides, and copper nitrate, have been disclosed for the synthesis of diverse bioactive and pharmacologically interesting N-containing heterocycles under the participation of transition metals. The well-known nitrogen sources, such as amines and amides, were used for the construction of indoles, isatins, and quinolones. Dihydrophthalazines, isoquinolines, indazoles, and pyrazoles were obtained from hydrazones, while various pyrimidine-containing heterocycles were afforded through regioselective C-H functionalizations using pyrimidine as the directing group. Recent research has focused on the chemistry of isocyanides to achieve several kinds of heterocyclic compounds with high efficiency under the catalysis of transition metals (Pd, Rh, Mn, Cu), through oxidative cyanation reactions, sequential isocyanide insertions into C-H, N-H, or O-H bonds, and tandem radical annulation. More recently, an efficient route to isoxazolines has been reported using copper nitrate as a novel nitrogen source.

Silver(i)-mediated three-component annulation reaction of [60]fullerene, sulfonylhydrazones, and nitriles: leading to diverse disubstituted [60]fullerene-fused dihydropyrroles

A novel Ag(i)-mediated three-component annulation reaction of C₆₀, sulfonylhydrazones, and nitriles is developed for the synthesis of diverse disubstituted C₆₀-fused dihydropyrroles.

The microwave-assisted ortho-alkylation of azine N-oxides with N-tosylhydrazones catalyzed by copper(i) iodide

A regioselective direct ortho-alkylation of azine N-oxides has been achieved under ligand-free conditions using copper(i) iodide and microwave conditions.

Access to steroidal pyridazines via modified thiohydrazides

Cytotoxic effects against breast cancer cells.

I₂-TBHP-catalyzed oxidative cross-coupling of N-sulfonyl hydrazones and isocyanides to 5-aminopyrazoles

I2-TBHP-catalyzed oxidative cross coupling of N-sulfonyl hydrazones with isocyanides has been realized for the synthesis of 5-aminopyrazoles through formal [4 + 1] annulation via in situ azoalkene formation. Notable features are the metal/alkyne-free strategy, C-C and C-N bond formation, atom economy, catalytic I2, broad functional group tolerance, good reaction yields, shorter time, and also applicability to one-pot methodology.

A simple and efficient synthesis of 9-arylfluorenes via metal-free reductive coupling of arylboronic acids and N-tosylhydrazones in situ

A general, yet efficient synthesis method of 9-arylfluorenes via metal-free reductive coupling of N-tosylhydrazones and arylboronic acids has been developed.

AgNO2-mediated cleavage of the N–N bond of sulfonylhydrazones and oxygen transfer: access to fulleroisoxazolines via radical cyclization with [60]fullerene

The first example involving cleavage of the N–N bond of sulfonylhydrazones is presented, and a new methodology for the synthesis of fulleroisoxazolines is developed.