Aryl Oximes Research Articles

Cobalt-catalyzed three-component assembly of aromatic oximes with substituted dienes and formaldehyde.

A cobalt-catalyzed three-component assembly of substituted aryl oximes with dienes and formaldehyde via C-H bond activation is described. This protocol affords highly regio- and chemoselective substituted homoallylic alcohols with moderate-to-excellent yields. The scope of this protocol has been extensively explored with various substituted aryl ketoximes and aldoximes. Butadiene and internally substituted dienes are also well compatible for this transformation. A plausible reaction mechanism is proposed to account for the present reaction and is supported by deuterium labeling studies.

Effect of ligand substituents on the reactivity pathways of copper(II) complexes towards electrocatalytic water oxidation.

The electrocatalytic water oxidation activity of three copper(II) complexes [Cu(L1H)(L1)](ClO4) (1), [Cu(L2H)(L2)(H2O)](ClO4) (2) and [Cu(L3H)(L2)](ClO4) (3) with aryl oxime ligands L1H, L2H and L3H [L1H = 1-(pyridin-2-yl)methanone oxime, L2H = 1-(pyridin-2-yl)ethanone oxime and L3H = 1-(pyridin-2-yl)propanone oxime] was investigated. All the three ligands have in common a pyridyl group attached to the carbon centre of the oxime moiety and differ in the second substituent attached to the carbon centre. Electrochemical investigation of the catalytic activity of complexes 1, 2 and 3 shows that the nature of the substituent attached to the carbon centre has an influence on the catalytic pathway and overall catalytic activity of these complexes.

Oxidative Cyclization of Oximes with Propargyl Alcohols toward Functionalized Isoquinoline N‐Oxides Synthesis

AbstractAn efficient and regioselective synthesis of various functionalized isoquinoline N‐oxides has been realized by Rh(III)‐catalyzed oxidative annulation of aryl oximes with tertiary propargyl alcohols. The current protocol features readily available starting materials, mild reaction conditions, broad substrate scope and wide functional group tolerance.

Mechanistic insights to define the directional role of hydrogen-bonding network between aryl oximes and propargyl alcohols in Rh(III) catalysis

The mechanism of the Cp*Rh(OAc)2-catalyzed C−H activation/annulation of acetophenone oxime and secondary propargyl alcohol was studied theoretically. Four elementary steps are involved as follows: C−H activation via concerted-metalation-deprotonation (CMD) mechanism, regioselective alkyne insertion, β-OH elimination and metal-free 6π electrocyclization. Importantly, density functional theory (DFT) calculations reveal that β-H elimination is inferior to β-OH elimination that is assisted by the directional hydrogen-bonding network between the two hydroxyl groups of the substrates. This noncovalent interaction also contributes to tuning the regioselectivity of alkyne insertion. Furthermore, the metal-free 6π electrocyclization rather than Rh-assisted cyclization gave the final product, isoquinoline N-oxides. The computationally supported mechanistic features were further validated by exploring substrate effects via replacing acetophenone oxime with O-methyl oxime and secondary propargyl alcohol with allyl alcohol, allenol and tertiary propargyl alcohol, respectively.

An organic photoredox catalyst promotedpara-selective C–H amination of aryl oximes

Direct C–H amination methods are essential because of the importance of aryl amine derivatives.

Rh(III)‐Catalyzed Enantioselective Intermolecular Aryl C—H Bond Addition to Aldehydes

Comprehensive SummaryThe direct addition of aryl C—H bond to carbon‐heteroatom double bond by transition‐metal‐catalyzed C—H activation has been extensively investigated in the past decade. However, the enantioselective intermolecular C—H addition to aldehyde has not yet been reported and is of significant challenge. Rh(III)‐catalyzed highly enantioselective intermolecular C—H addition of aryl oxime ethers to glyoxylates is reported. Chiral mandelic acid esters were obtained in excellent yields (up to 98%) and enantioselectivity (up to 99% ee) in the presence of a chiral CpRh(III) catalyst under mild conditions. The substituents on the Cp ring and BINOL skeleton were responsible for the high enantioselectivity observed. The method displays a broad substrate scope and good functionality tolerance. These results provide not only a promising C—H addition approach but also a proof of concept for developing broader asymmetric C—H addition reactions.

Visible-Light-Promoted Cross-Coupling of O-Aryl Oximes and Nitrostyrenes to Access Cyanoalkylated Alkenes.

A photoinduced, photocatalyst-free cyanoalkylation of nitrostyenes was explored, affording a series of cyanoalkylated alkenes in moderate to good yields. Mechanistic studies reveal that an electron donor-acceptor complex formed between O-aryl oximes and DIPEA is presumably involved in this process. The excellent functional group compatibility of this newly designed synthetic protocol allows for cyanoalkylation of structurally varied substrates, which offers an eco-friendly pathway for the assembly of cyanoalkylated alkenes.

A catalytic regioselective procedure for the synthesis of aryl oximes in the presence of palladium nanoparticles

The synthesis of aryl oximes from aryl aldehyde derivatives was carried out using hydroxylamine hydrochloride and aluminum oxy hydroxide-supported palladium (Pd/AlO(OH) nanoparticles. The procedure is revealed via the regioselective synthesis of oxime derivatives in a polar solvent mixture resulting in high yields at room temperature.

Rhodium(iii)-catalyzed successive C(sp2)–H and C(sp2)–C(sp2) bond activation of aryl oximes: synthetic and mechanistic studies

A rhodium(iii)-catalyzed redox-neutral reaction of aryl oximes and internal alkynes to generate novel N-(2-cyanoaryl) indanone imines.

Photocatalyzed Triplet Sensitization of Oximes Using Visible Light Provides a Route to Nonclassical Beckmann Rearrangement Products.

Oximes are valuable synthetic intermediates for the preparation of a variety of functional groups. To date, the stereoselective synthesis of oximes remains a major challenge, as most current synthetic methods either provide mixtures of E and Z isomers or furnish the thermodynamically preferred E isomer. Herein we report a mild and general method to achieve Z isomers of aryl oximes by photoisomerization of oximes via visible-light-mediated energy transfer (EnT) catalysis. Facile access to (Z)-oximes provides opportunities to achieve regio- and chemoselectivity complementary to those of widely used transformations employing oxime starting materials. We show an enhanced one-pot protocol for photocatalyzed oxime isomerization and subsequent Beckmann rearrangement that enables novel reactivity with alkyl groups migrating preferentially over aryl groups, reversing the regioselectivity of the traditional Beckmann reaction. Chemodivergent N- or O- cyclizations of alkenyl oximes are also demonstrated, leading to nitrones or cyclic oxime ethers, respectively.

Remote C−H Pyridylation of Hydroxamates through Direct Photoexcitation of O‐Aryl Oxime Pyridinium Intermediates

AbstractHerein, we report an efficient strategy for the remote C−H pyridylation of hydroxamates with excellent ortho‐selectivity by designing a new class of photon‐absorbing O‐aryl oxime pyridinium salts generated in situ from the corresponding pyridines and hydroxamates. When irradiated by visible light, the photoexcitation of oxime pyridinium intermediates generates iminyl radicals via the photolytic N−O bond cleavage, which does not require an external photocatalyst. The efficiency of light absorption and N−O bond cleavage of the oxime pyridinium salts can be modulated through the electronic effect of substitution on the O‐aryl ring. The resultant iminyl radicals enable the installation of pyridyl rings at the γ‐CN position, which yields synthetically valuable C2‐substituted pyridyl derivatives. This novel synthetic approach provides significant advantages in terms of both efficiency and simplicity and exhibits broad functional group tolerance in complex settings under mild and metal‐free conditions.

The local and natural sources in synthetic methods: the practical synthesis of aryl oximes from aryl aldehydes under catalyst-free conditions in mineral water

The local and natural sources in synthetic methods: the practical synthesis of aryl oximes from aryl aldehydes under catalyst-free conditions in mineral water

Rhodium‐Catalyzed C−H Activation/Annulation Cascade of Aryl Oximes and Propargyl Alcohols to Isoquinoline N‐Oxides

AbstractA β‐hydroxy elimination instead of common oxidization to carbonyl group in secondary propargyl alcohols was successfully developed to form 2‐benzyl substituted isoquinoline N‐oxides by a Rhodium‐catalyzed C−H activation and annulation cascade, in which moderate to excellent yields (up to 92%) could be obtained under mild reaction conditions, along with good regioselectivity, broad generality and applicability.magnified image

Synthesis and SAR Study of Simple Aryl Oximes and Nitrofuranyl Derivatives with Potent Activity Against Mycobacterium tuberculosis

Background: Oximes and nitrofuranyl derivatives are particularly important compounds in medicinal chemistry. Thus, many researchers have been reported to possess antibacterial, antiparasitic, insecticidal and fungicidal activities. Methods: In this work, we report the synthesis and the biological activity against Mycobacterium tuberculosis H37RV of a series of fifty aryl oximes, ArCH=N-OH, I, and eight nitrofuranyl compounds, 2-nitrofuranyl-X, II. Results: Among the oximes, I: Ar = 2-OH-4-OH, 42, and I: Ar = 5-nitrofuranyl, 46, possessed the best activity at 3.74 and 32.0 µM, respectively. Also, 46, the nitrofuran compounds, II; X = MeO, 55, and II: X = NHCH2Ph, 58, (14.6 and 12.6 µM, respectively), exhibited excellent biological activities and were non-cytotoxic. Conclusion: The compound 55 showed a selectivity index of 9.85. Further antibacterial tests were performed with compound 55 which was inactive against Enterococcus faecalis, Klebisiella pneumonae, Pseudomonas aeruginosa, Staphylococcus aureus, Salmonella typhymurium and Shigella flexneri. This study adds important information to the rational design of new lead anti-TB drugs. Structure-activity Relationship (SAR) is reported.

Terminal Alkyne-Assisted One-Pot Synthesis of Arylamidines: Carbon Source of the Amidine Group from Oxime Chlorides.

A terminal alkyne-assisted protocol for the one-pot formation of a diverse range of arylamidines from a novel cascade reaction of in situ generated nitrile oxides, sulfonyl azides, terminal alkynes, and water by [3 + 2] cycloaddition and ring opening sequence was developed. The use of aryl oxime chlorides as the carbon source of the amidine group and the addition of water proved to be critical for the reaction. Moreover, terminal alkynes, which can lead to high yields of products by employing a less amount, may play a catalytic role in the reaction. A broader range of substrates was investigated.

Ligand assisted electrocatalytic water oxidation by a copper(ii) complex in neutral phosphate buffer.

The electrocatalytic water oxidation activity of a copper(ii) complex, 1, [Cu(L1H)(L1)(OH2)](ClO4), with a redox active aryl oxime ligand, L1H [L1H = 1-(pyridin-2-yl) ethanone oxime] has been investigated. Complex 1 shows a remarkably high turnover frequency of ∼100 s-1 in neutral phosphate buffer at about 675 mV overpotential with ∼94% faradaic efficiency. Electrochemical analysis suggests the involvement of a ligand moiety in a proton-coupled-electron-transfer (PCET) step during the catalytic cycle of complex 1, which in turn provides a route for accumulation of high oxidizing equivalents at the reaction center.

Rhodium(III)‐Catalyzed C–H Alkylation/Nucleophilic Addition Domino Reaction

A C–H alkylation/nucleophilic addition manifold with synthetically useful aryl oximes and pyrazoles was realized by rhodium(III) catalysis under remarkably mild reaction conditions. Valuable β‐acyl substituted arylbutanoates were obtained in moderate to good yields. This strategy is characterized by excellent atom‐ and step‐economy, high chemo‐ and site‐selectivity, a broad substrate scope, and a wide functional group tolerance.

Palladium-Catalyzed Redox-Neutral N-O/C(sp3)-H Functionalization of Aryl Oximes with Isocyanides.

A redox-neutral palladium-catalyzed N-O/C(sp3)-H functionalization of aryl oximes with isocyanides has been developed. Various pyrrole derivatives were prepared in good to excellent yields through oxime carbamate as a key intermediate and internal oxidant in this process. Furthermore, this transformation also features readily available starting materials, good functional group tolerance, and excellent regioselectivity.

Carboxylate-Enhanced Rhodium(III)-Catalyzed Aryl C-H Alkylation with Conjugated Alkenes under Mild Conditions.

Rhodium(III)-catalyzed C-H bond functionalization for the synthesis of β-aryl aldehydes and ketones from (hetero)aryl oximes, pyri(mi)dine, as well as pyrazoles and α,β-unsaturated carbonyl compounds has been developed under exceedingly mild reaction conditions. Thus, the versatile rhodium(III) catalysis features high step- and atom-economy, oxidant-free reaction conditions, and broad substrate scope.

ChemInform Abstract: Palladium‐Catalyzed C—H Functionalization of Aromatic Oximes: A Strategy for the Synthesis of Isoquinolines.

AbstractThe cross‐coupling of aryl oximes with aryl substituted vinyl azides to give 3‐substituted isoquinolines is reported.