Mn- and Co-Catalyzed Aminocyclizations of Unsaturated Hydrazones Providing a Broad Range of Functionalized Pyrazolines

Electrocatalytic dehydrogenative and defluorinative coupling between aldehyde-derived N,N-dialkylhydrazones and fluoromalonates: synthesis of 2-pyrazolines

An electrocatalytic synthesis of 2-pyrazolines via dehydrogenative and defluorinative cross-coupling reactions between (hetero)arylaldehyde-derived N,N-dialkylhydrazones and fluoromalonates is disclosed. Salient features of this work include (i) readily available starting materials, (ii) practical reaction conditions, and (ii) a formal oxidative (4 + 1)-cycloaddition via triple C-H bond functionalization. Cyclic voltammetry analyses support the electrocatalytic formation of an α-fluoromalonyl radical.

Integrating Olefin Carboamination and Hofmann-Löffler-Freytag Reaction by Radical Deconstruction of Hydrazonyl N-N Bond

As a type of elementary organic compounds containing N-N single bond, hydrazone involved chemical conversions are extremely extensive, but they are mainly limited to N2-retention and N2-removal modes. We report herein an unprecedented protocol for the realization of division utilization of the N2-moiety of hydrazone by a radical facilitated N-N bond deconstruction strategy. This new conversion mode enables the successful combination of alkene carboamination and Hofmann-Löffler-Freytag reaction by the reaction of N-homoallyl mesitylenesulfonyl hydrazones with ethyl difluoroiodoacetate under photocatalytic redox neutral conditions. Mechanism studies reveal that the reaction undergoes a radical relay involving addition, crucial remote imino-N migration and H-atom transfer. Consequently, a series of structurally significant ϵ-N-sulphonamide-α,α-difluoro-γ-amino acid esters are efficiently produced via continuous C-C bond and dual C-N bonds forging.

Molecular Co-Catalyst Confined within a Metallacage for Enhanced Photocatalytic CO2 Reduction

The construction of structurally well-defined supramolecular hosts to accommodate catalytically active species within a cavity is a promising way to address catalyst deactivation. The resulting supramolecular catalysts can significantly improve the utilization of catalytic sites, thereby achieving a highly efficient chemical conversion. In this study, the Co-metalated phthalocyanine (Pc-Co) was successfully confined within a tetragonal prismatic metallacage, leading to the formation of a distinctive type of supramolecular photocatalyst (Pc-Co@Cage). The host-guest architecture of Pc-Co@Cage was unambiguously elucidated by single-crystal X-ray diffraction (SCXRD), NMR, and ESI-TOF-MS, revealing that the single cobalt active site can be thoroughly isolated within the space-restricted microenvironment. In addition, we found that Pc-Co@Cage can serve as a homogeneous supramolecular photocatalyst that displays high CO2 to CO conversion in aqueous media under visible light irradiation. This supramolecular photocatalyst exhibits an obvious improvement in activity (TONCO = 4175) and selectivity (SelCO = 92%) relative to the nonconfined Pc-Co catalyst (TONCO = 500, SelCO = 54%). The present strategy provided a rare example for the construction of a highly active, selective, and stable photocatalyst for CO2 reduction through a cavity-confined molecular catalyst within a discrete metallacage.

Novel pyrazoline linked acyl thiourea pharmacophores as antimicrobial, urease, amylase and α-glucosidase inhibitors: design, synthesis, SAR and molecular docking studies

In the present work, a small library of novel pyrazolinyl-acyl thiourea (5a-j) was designed and synthesized through a multistep sequence and the synthesized compounds were screened for their antifungal, antibacterial and antioxidant activities as well as urease, amylase and α-glucosidase inhibitory activities. The synthesized series (5a-o) was characterized using a combination of spectroscopic techniques, including FT-IR, 1H NMR and 13C NMR. All compounds (5a-j) were found to have significant potency against urease, α-glucosidase, α-amylase, and DPPH. The synthesized compounds were also screened for potential antibacterial and anti-fungal inhibition activities. IC50 values for all the prepared compounds for urease, α-glucosidase, amylase, and DPPH inhibition were determined and derivatives 5b and 5g were found to be the most potent urease inhibitors with IC50 values of 54.2 ± 0.32 and 43.6 ± 0.25 μM, respectively. Whilst compound 5b (IC50 = 68.3 ± 0.11 μM) is a potent α-glucosidase inhibitor, compound 5f (90.3 ± 1.08 μM) is a potent amylase inhibitor and compound 5b (103.4 ± 1.15 μM) is a potent antioxidant. The different substitutions on the phenyl ring were the basis for structure-activity relationship (SAR) study. The molecular docking study was performed for the confirmation of binding interactions.

Cu(II)-Catalyzed Aminocyclization of N-Propargyl Hydrazones to Substituted Pyrazolines

An efficient route for the copper(II)-catalyzed synthesis of substituted pyrazolines from readily accessible N-propargyl hydrazones has been reported under open flask conditions via intramolecular C-N bond formation. N-acyl and N-tosyl-substituted pyrazolines have been prepared in moderate to excellent yields. Mechanistic investigations using NMR, high-resolution mass spectrometry (HRMS), and Hammett analyses suggest that the Cu(II) catalyst generally acts as a Lewis acid to form an iminium-ion intermediate via cyclization, which afforded the desired pyrazolines upon hydrolysis. One progesterone receptor antagonist has also been synthesized utilizing this reaction methodology.

Cobalt-Catalyzed Aerobic Aminocyclization of Unsaturated Amides for the Synthesis of Functionalized γ- and δ-Lactams

We report the cobalt-catalyzed aminocyclization of unsaturated N-acyl sulfonamides in the presence of oxygen to provide γ- and δ-lactam aldehydes. Use of an optically active cobalt catalyst resulted in the formation of enantiomerically enriched γ-and δ-lactam alcohols. The γ-lactam aldehydes and alcohols obtained were elaborated into useful building blocks.

Oxygen-Promoted 6-endo-trig Cyclization of β,γ-Unsaturated Hydrazones/Ketoximes with Diazonium Tetrafluoroborates for Pyridazin-4(1H)-ones/Oxazin-4(1H)-ones

An oxidative 6-endo-trig cyclization and [2 + 2] cycloaddition of β,γ-unsaturated hydrazones/ketoximes and diazonium tetrafluoroborates for a synthetic strategy to pyridazin-4(1H)-ones/oxazin-4(1H)-ones under metal-free conditions is presented in a one-pot procedure. This protocol features excellent functional group tolerance and remarkable regioselectivity. A mechanistic study has been verified via 18O labeling and the H218O labeling method, in which O2 acts as both a reaction component and an oxidant.

Annulative Aminosulfonylation of Unactivated Alkenes for Accessing Pyrazolines via Multicomponent SO2 Insertion

A direct arylsulfonylation of β,γ-unsaturated hydrazones method, in which sulfonated pyrazolines are accessed by a three-component reaction of β,γ-unsaturated hydrazones, DABSO, and aryldiazonium tetrafluoroborates, has been developed without external oxidants or catalysts. This transformation is triggered by the formation of arylsulfonyl radicals in situ from the reaction of aryldiazonium tetrafluoroborates and DABSO, and is enabled by controllable generation of C center radical, in which DABSO was utilized as the sulfone source and an oxidant in this radical-mediated cascaded reaction. A wide range of substrates can be applied in this process to afford pyrazolines in good yield, and it is amenable for gram-scale synthesis.

Copper-Catalyzed Enantioselective Aerobic Alkene Aminooxygenation and Dioxygenation: Access to 2-Formyl Saturated Heterocycles and Unnatural Proline Derivatives

Alkene aminooxygenation and dioxygenation reactions that result in carbonyl products are uncommon, and protocols that control absolute stereochemistry are rare. We report herein catalytic enantioselective alkene aminooxygenation and dioxygenation that directly provide enantioenriched 2-formyl saturated heterocycles under aerobic conditions. Cyclization of substituted 4-pentenylsulfonamides, catalyzed by readily available chiral copper complexes and employing molecular oxygen as both oxygen source and stoichiometric oxidant, directly provides chiral 2-formyl pyrrolidines efficiently. Reductive or oxidative workup of these aldehydes provides their respective amino alcohols or amino acids (unnatural prolines). Enantioselective synthesis of an indoline and isoquinolines is also demonstrated. Concurrently, cyclization of various alkenols under similar conditions provides 2-formyl tetrahydrofurans, phthalans, isochromans, and morpholines. The nature of the copper ligands, the concentration of molecular oxygen, and the reaction temperature all impact the product distribution. Chiral nitrogen and oxygen heterocycles are common components of bioactive small molecules, and these enabling technologies provide access to saturated heterocycles functionalized with ready-to-use carbonyl electrophiles.

Cobalt-catalyzed chemoselective dehydrogenation through radical translocation under visible light

The transformations that allow the direct removal of hydrogen from their corresponding saturated counterparts by the dehydrogenative strategy are a dream reaction that has remained largely underexplored. In this report, a straightforward and robust cobaloxime-catalyzed photochemical dehydrogenation strategy via intramolecular HAT is described for the first time. The reaction proceeds through an intramolecular radical translocation followed by the cobalt assisted dehydrogenation without needing any other external photosensitizers, noble-metals or oxidants. With this approach, a series of valuable unsaturated compounds such as α,β-unsaturated amides, enamides and allylic and homoallylic sulfonamides were obtained in moderate to excellent yields with good chemo- and regioselectivities, and the synthetic versatility was demonstrated by a range of transformations. And mechanistic studies of the method are discussed.

The dehydrogenative reactions proceeded through selective 1,n-hydrogen atom transfer (n = 5–7) for remote C–H activation by cobaloxime catalysis.

Cobalt-Catalyzed Cyclization of Unsaturated N-Acyl Sulfonamides: a Diverted Mukaiyama Hydration Reaction

The cycloisomerization of β-, γ-, and δ-unsaturated N-acyl sulfonamides to N-sulfonyl lactams and imidates is reported. This transformation is effected in the presence of a Co^III(salen) catalyst using t-BuOOH or air as the oxidant. The method shows good functional group tolerance (alkyl, aryl, heteroaryl, ether, N-Boc) and furnishes an underexplored class of cyclic building blocks. The strong solvent dependence of the transformation is investigated, and the synthetic versatility of the N-sulfonyl imidate product class is highlighted.

Synthesis of dihydropyrazoles enabled by Pd-catalyzed carboamination of alkenyl hydrazones with alkenyl and aryl halides

The synthesis of dihydropyrazoles enabled by Pd-catalyzed carboamination of alkenyl hydrazones with alkenyl or aryl halides is described. This method provides a practical and efficient route towards the synthesis of functionalized dihydropyrazoles.