Domino Reactions Involving the Branched C–N and C═C Cleavage of Enaminones Toward Pyridines Synthesis

Deconstructive annulation mediated one-pot synthesis of xanthene derivatives

Direct conversion of naphthoxazines to diverse xanthene derivatives was achieved under one-pot operation through deconstructive annulation methodology. Sequential oxidative C(sp3)-O/C(sp3)-N cleavage followed by intramolecular/intermolecular annulation reaction was carried out under aerobic reaction conditions. Mechanistic analyses performed on the substrate revealed that the C(sp3)-O bond cleavage supersedes the C(sp3)-N bond scission. The in situ generated Betti base intermediate through the C(sp3)-O cleavage was successfully isolated. Based on a molecular docking investigation, the intermolecular annulated products demonstrated good α-glucosidase inhibitory properties.

One-pot domino synthesis of five- and six-membered fused dihydropyridines promoted by PPh3-NBS in aqueous medium

A facile one-pot synthesis of five- and six-membered fused dihydropyridines such as chromenodihydropyridines, pyrazolodihydropyridines and isoxazolopyridines was accomplished for the first time by employing PPh₃-NBS via a formal [3 + 2 + 1] cycloaddition of 1,3-bisnucleophiles (i.e., 2-aminochromone, 4-aminochromone, 5-aminopyrazole and 5-aminoisoxazole), β-enaminones and aldehydes in aqueous medium. The present approach involves a Michael type addition followed by intramolecular cyclization leading to the formation of two new C-C bonds and one C-N bond. High compatibility and excellent yields are the advantages of this protocol.

Recent advances in transition metal-free annulation toward heterocycle diversity based on the C-N bond cleavage of enaminone platform

The enaminones and analogous stable enamines are well known as platform building blocks in organic synthesis for construction of heterocyclic compounds, especially N-heterocycles. To date, especially enaminones have been successfully...

BF3·OEt2 catalyzed chemoselective CC bond cleavage of α,β-enones: an unexpected synthesis of 3-alkylated oxindoles and spiro-indolooxiranes

A BF₃·OEt₂ catalyzed highly chemoselective formal CC double bond cleavage reaction of α,β-enones with diazoamides for the synthesis of 3-alkylated oxindoles is developed. Boron trifluoride etherate is found to be an effective catalyst for the chemoselective C_α-C_β cleavage of enones to obtain 3-alkylated oxindoles. The product formation indicates a selective β-carbon elimination pathway of α,β-enones using the inexpensive BF₃·OEt₂ as a catalyst, transition metal-free conditions, an open-air environment, good functional tolerance and broad substrate scope. The synthetic utility of this protocol is highlighted by synthesizing spiro-indolooxiranes.

Synthesis of 15N-labeled heterocycles via the cleavage of C-N bonds of anilines and glycine-15N

A nitrogen replacement process that directly incorporates the 15N atom of glycine-15N into anilines was reported. The process involves a Csp2-N bond cleavage of anilines driven by dearomatization and a Csp3-N bond cleavage of glycine-15N driven by aromatization. A variety of 15N-labeled aromatic heterocycles can be prepared via this process.

Regioselective construction of pyridazine and tetrahydrocinnoline derivatives via [4 + 2] cycloaddition–elimination with α-halogeno hydrazones and enaminones

Herein, we report the de novo construction of pyridazine scaffolds via a [4 + 2] cycloaddition–elimination reaction with α-halogeno hydrazones and enaminones.

Synthesis of α-Keto Thioamides by Metal-Free C═C Bond Cleavage in Enaminones Using Elemental Sulfur

An unprecedented method for cleaving the C═C bond in N, N-disubstituted enaminones in the presence of elemental sulfur and N, N-dimethyl-4-aminopyridine is disclosed. Without using any metal catalyst or additive, the cascade functionalization of both C═C and C-H bonds takes place to enable the formation of new C═S and C-N bonds, thus providing a facile and practical method for the synthesis of N, N-disubstituted α-keto thioamides.

Achieving Efficient Triplet Exciton Utilization with Large Δ EST and Nonobvious Delayed Fluorescence by Adjusting Excited State Energy Levels

Enhancing the rate of reverse intersystem crossing ( k_risc) and the rate of radiative transition ( k_r) has been regarded as the key to improve molecular design strategy in the field of thermally activated delayed fluorescence (TADF) materials. Herein, two sky-blue donor-acceptor (D-A)-type TADF materials, namely, CzDCNPy and tBuCzDCNPy, were designed following a strategy of controlling the energy difference among the charge-transfer singlet state (¹CT), local exciton triplet state (³LE), and charge-transfer triplet state (³CT). Significantly different from most previously reported TADF materials, large values of k_r and k_risc and a nearly 100% exciton utilization efficiency were simultaneously achieved despite nonobvious delayed fluorescence and a large value of the singlet-triplet energy difference (Δ E_ST) being observed. This work presents a view that photoinduced delayed fluorescence and a small Δ E_ST are sufficient but not necessary for TADF materials. It also provides a reference that the high-energy ³LE state plays a key role in the RISC process in electroluminescence.

Synthesis of Symmetric and Unsymmetric Secondary Amines from the Ligand-Promoted Ruthenium-Catalyzed Deaminative Coupling Reaction of Primary Amines

The catalytic system generated in situ from the tetranuclear Ru-H complex with a catechol ligand (1/L1) was found to be effective for the direct deaminative coupling of two primary amines to form secondary amines. The catalyst 1/L1 was highly chemoselective for promoting the coupling of two different primary amines to afford unsymmetric secondary amines. The analogous coupling of aniline with primary amines formed aryl-substituted secondary amines. The treatment of aniline- d₇ with 4-methoxybenzylamine led to the coupling product with significant deuterium incorporation on CH₂ (18% D). The most pronounced carbon isotope effect was observed on the α-carbon of the product isolated from the coupling reaction of 4-methoxybenzylamine (C(1) = 1.015(2)). A Hammett plot was constructed from measuring the rates of the coupling reaction of 4-methoxyaniline with a series of para-substituted benzylamines 4-X-C₆H₄CH₂NH₂ (X = OMe, Me, H, F, CF₃) (ρ = -0.79 ± 0.1). A plausible mechanistic scheme has been proposed for the coupling reaction on the basis of these results. The catalytic coupling method provides an operationally simple and chemoselective synthesis of secondary amine products without using any reactive reagents or forming wasteful byproducts.

Selective access to dipyrazolo-fused pyridines via formal [3 + 2 + 1] heteroannulation of methyl ketones with pyrazol-5-amines

A fascinating new form of the Hantzsch reaction with methyl ketones and pyrazol-5-amines for the selective synthesis of dipyrazolo-fused pyridines has been discovered.

One-Pot Synthesis of Functionalised 4-Spiro-1,4-Dihydropyridines Via [1+2+1+2]-Cyclisation

A simple and efficient approach for the synthesis of 4-spiro-1,4-DHP derivatives has been developed, involving one-pot three-component reaction of isatins, N,N-dimethylenaminones with ammonium acetate in EtOH–water solution promoted by acetic acid. Compared with the previous [1+2+3]-cyclisation method, this [1+2+1+2]-cyclisation procedure has advantages as it is more environmentally friendly, has easier operational simplicity, and requires milder reaction conditions. Moreover, these novel compounds have been obtained in moderate to good yields and their structures have been confirmed by 1H NMR, 13C NMR and IR and HRMS spectroscopy.

Regioselective three-component synthesis of 2,3-disubstituted quinolines via the enaminone modified Povarov reaction

The enaminone modified three-component Povarov reactions enable the regioselective synthesis of 2,3-disubstituted quinolines.

Chemoselective C(α)–C(β) bond cleavage of saturated aryl ketones with amines leading to α-ketoamides: a copper-catalyzed aerobic oxidation process with air

An unprecedented chemoselective C(α)–C(β) bond cleavage of simple saturated aryl ketones with amines leading to α-ketoamidesvia a copper-catalyzed aerobic oxidation process with air has been disclosed.

Metal-Free Synthesis of Fully Substituted Pyridines via Ring Construction Based on the Domino Reactions of Enaminones and Aldehydes

An unprecedented domino reaction involving primary enaminones/enaminoesters and aldehydes has been developed for the synthesis of fully substituted pyridines. The construction of the products has been accomplished via the cascade generation of two C-C and one C-N bond by simply using TfOH as a promoter.

Copper-catalyzed, hypervalent iodine mediated CC bond activation of enaminones for the synthesis of α-keto amides

An unprecedented approach toward the general synthesis of α-keto amides has been established by tailoring the CC double bond of enaminones in the presence of CuI and hypervalent iodine.

FeCl3-Catalyzed Combinatorial Synthesis of Functionalized Spiro[Indolo-3,10'-indeno [1,2-b]quinolin]-trione Derivatives

An efficient, inexpensive, environmentally friendly and high yield one-pot route to new spiro[indolo-3,10'-indeno [1,2-b]quinolin]-trione derivatives has been developed, involving three-component reaction of enaminones, N-substituted isatins and Indane-1,3-dione catalyzed by FeCl3. The approach to this spiro-heterocycle is noteworthy because it results in the formation of three new σ (two C-C and one C-N) bonds in a single operation, leading to the construction of novel spiro skeleton. This method works on a large scale in excellent yields.

Ammonium iodide-promoted cyclization of ketones with DMSO and ammonium acetate for synthesis of substituted pyridines

A convenient and efficient method has been developed for the construction of substituted pyridines via ammonium iodide-promoted cyclization of ketones with DMSO and ammonium acetate, employing DMSO as the source of C4 or C6.

Regioselective three-component reactions of enaminones, 2-aminopyridines and enals for the synthesis of 1,2-dihydropyridines

A novel regioselective, metal-free and broadly applicable three-component approach for the synthesis of 1,2-dihydropyridines has been established.

Copper-catalyzed three-component reactions of phenols, acyl chlorides and Wittig reagents for the synthesis of β-aryloxyl acrylates

A new protocol towards the diversity-oriented synthesis of β-aryloxyl acrylates has been developed using simple reactants and catalyst.

Synthesis of 2,4-diarylsubstituted-pyridines through a Ru-catalyzed four component reaction

2,4-Diarylsubstituted pyridines were prepared from acetophenones, ammonium acetate and DMF under an oxygen atmosphere.