Simple Imines Research Articles

Spectroscopic evidence for 1,2-diiminoethane - a key intermediate in imidazole synthesis.

Simple imines and diimines are common building blocks in organic synthesis, but the compound class is spectroscopically not well characterized. Herein we report the formation of the simplest diimine, namely 1,2-diiminoethane, as well as spectroscopic characterization by cryogenic matrix isolation IR and UV/Vis spectroscopy. Three conformers of 1,2-diiminoethane form after UV irradiation of 1,2-diazidoethane by N2 extrusion at 3 K in solid argon and can be photochemically interconverted. In a matrix isolation pyrolysis experiment at 600 °C with 1,2-diazidoethane as the starting material we observe hydrogen cyanide and formaldimine as the main decomposition products. All experimental findings are supported by deuterium labeling experiments and B3LYP/6-311++G(2d,2p) calculations. Irradiation of 1,2-diazidoethane in aqueous solution leads to the formation of imidazoles as indicated by NMR spectroscopy and GC-MS analysis. Our results underline the key role of diimines as building blocks in N-heterocyclic chemistry.

Origin of rate enhancement and asynchronicity in iminium catalyzed Diels-Alder reactions.

The Diels–Alder reactions between cyclopentadiene and various α,β-unsaturated aldehyde, imine, and iminium dienophiles were quantum chemically studied using a combined density functional theory and coupled-cluster theory approach. Simple iminium catalysts accelerate the Diels–Alder reactions by lowering the reaction barrier up to 20 kcal mol−1 compared to the parent aldehyde and imine reactions. Our detailed activation strain and Kohn–Sham molecular orbital analyses reveal that the iminium catalysts enhance the reactivity by reducing the steric (Pauli) repulsion between the diene and dienophile, which originates from both a more asynchronous reaction mode and a more significant polarization of the π-system away from the incoming diene compared to aldehyde and imine analogs. Notably, we establish that the driving force behind the asynchronicity of the herein studied Diels–Alder reactions is the relief of destabilizing steric (Pauli) repulsion and not the orbital interaction between the terminal carbon of the dienophile and the diene, which is the widely accepted rationale.

Ruthenium(0)-sequential catalysis for the synthesis of sterically hindered amines by C-H arylation/hydrosilylation.

We report sequential ruthenium(0)-catalysis for the synthesis of sterically-hindered amines via direct C-H arylation of simple imines and imine hydrosilylation. The method involves direct C-H arylation under neutral conditions with organoboranes enabled by ruthenium(0) catalysis. The catalytic hydrosilylation was performed in a one-pot fashion using Et3SiH. The reaction is compatible with a broad range of electronically- and sterically-varied imines, enabling rapid production of valuable biaryl amines in good to excellent yields. The method constitutes a two-step, one-pot procedure to synthesize sterically-hindered amines from aldehydes. The utility of this atom-economic strategy is demonstrated in one-pot, three-component coupling, direct in situ aldehyde arylation and the use of transfer hydrogenation.

Secondary amine salt catalyzed controlled activation of 2-deoxy sugar lactols towards alpha-selective dehydrative glycosylation.

A new organocatalytic glycosylation method exploiting the lactol functionality has been disclosed. The catalytic generation of glycosyl oxacarbenium ions from lactols under forcible conditions via weakly Brønsted-acidic, readily available secondary amine salts affects the diastereoselective glycosylation of 2-deoxypyranoses and furanoses. This operationally simple iminium catalyzed activation of 2-deoxy hemi-acetals is a potential alternative to the existing cumbersome methods that need specialized handling. The mechanisms for this unique transformation and kinetic/thermodynamic effects have been discussed based on both experimental evidence and theoretical studies.

Nitrogenated Azaphilone Derivatives through a Silver-Catalysed Reaction of Imines from ortho-Alkynylbenzaldehydes.

Nitrogenated azaphilones are interesting natural products with a wide range of applications. The structure of these compounds is characterized by the presence of an isoquinolinone framework. Here, we describe a new multicomponent silver-catalysed reaction that allows the transformation of simple imines derived from ortho-alkynylbenzaldehydes into complex nitrogenated azaphilone-type molecules in a straightforward way. This atom-economical process is high yielding, technically very simple and proceeds through a series of cascade processes that imply cycloisomerisation and formal cross-coupling reactions. This conceptually new process formally involves the synchronised catalytic generation and selective coupling of a nucleophile (isoquinolinone) and an electrophile (isoquinolinium). Some interesting colour properties of the synthesized azaphilone-type molecules are discussed.

ChemInform Abstract: Copper‐Catalyzed Cascade Reaction via Intramolecular Hydroamination Cyclization of Homopropargylic Amines and Intermolecular Povarov Reaction with Imines.

AbstractA series of hexahydro‐1H‐pyrrolo[3,2‐c]quinoline derivatives is synthesized in good to high yields by a one‐pot cascade reaction of homopropargylic amines with simple imines in the presence of Cu(OTf)2.

Enantioselective Generation of Adjacent Stereocenters in a Copper‐Catalyzed Three‐Component Coupling of Imines, Allenes, and Diboranes

AbstractA highly enantio‐ and diastereoselective copper‐catalyzed three‐component coupling affords the first general synthesis of homoallylic amines bearing adjacent stereocenters from achiral starting materials. The method utilizes a commercially available NHC ligand and copper source, operates at ambient temperature, couples readily available simple imines, allenes, and diboranes, and yields high‐value homoallylic amines that exhibit versatile amino, alkenyl, and boryl units.

Enantioselective Generation of Adjacent Stereocenters in a Copper-Catalyzed Three-Component Coupling of Imines, Allenes, and Diboranes.

A highly enantio‐ and diastereoselective copper‐catalyzed three‐component coupling affords the first general synthesis of homoallylic amines bearing adjacent stereocenters from achiral starting materials. The method utilizes a commercially available NHC ligand and copper source, operates at ambient temperature, couples readily available simple imines, allenes, and diboranes, and yields high‐value homoallylic amines that exhibit versatile amino, alkenyl, and boryl units.

Iodine(III)-Catalyzed Cascade Reactions Enabling a Direct Access to β-Lactams and α-Hydroxy-β-amino Acids.

In the presented method, a one-pot metal-free access to β-lactams is provided. The developed strategy employs a hypervalent iodine(III)-triggered bromination/rearrangement/cyclization cascade reaction that allows the straightforward synthesis of a broad range of structurally different lactams from cheap and easily available imides. This triple cascade reaction is furthermore extendable by an in situ ring-opening reaction, giving direct access to isoserine derivatives from simple imines in a four-step, one-pot reaction.

Copper-Catalyzed Cascade Reaction via Intramolecular Hydroamination Cyclization of Homopropargylic Amines and Intermolecular Povarov Reaction with Imines.

A new one-pot cascade reaction of homopropargylic amines with simple imines is developed in the presence of Cu(OTf)2 and affords a series of hexahydro-1H-pyrrolo[3,2-c]quinoline derivatives in good to high yields. This reaction proceeds through an intramolecular hydroamination cyclization of homopropargylic amine to generate a highly reactive dihydropyrrole intermediate in situ. It subsequently reacts with imine via an intermolecular inverse-electron-demand aza-Diels-Alder reaction and a 1,3-H shift to give the fused pyrroloquinoline structures, forming two new C-C bonds and one C-N bond and one N-H bond.

Photo- and Metallo-responsive N-Alkyl α-Bisimines as Orthogonally Addressable Main-Chain Functional Groups in Metathesis Polymers.

N-alkyl α-bisimines were employed as main-chain functional groups in acyclic diene metathesis (ADMET)-polymers, conferring dual responsiveness for the controlled switching of the polymeric particle shape with light and metal ions. Photochemical Z/E-isomerization leads to a significant and reversible change in hydrodynamic volume, thus introducing simple imines as novel photoswitches for light-responsive materials. Mild imine-directed CH activation by Pd(OAc)2 is demonstrated as a new single-chain nanoparticle (SCNP) folding process, enabling a controlled atom- and step-economic SCNP synthesis. The combination of light- and metallo-responsiveness in the same polymer provides the ability for orthogonal switching, a valuable tool for advanced functional material design.

Dehydrogenative N-incorporation: a direct approach to quinoxaline N-oxides under mild conditions.

An efficient method for the synthesis of quinoxaline N-oxides proceeds by the dehydrogenative N-incorporation of simple imines by C(sp(2))-H and C(sp(3))-H bond functionalization. The overall transformation involves the cleavage of three C-H bonds. The reaction is easily handled and proceeds under mild conditions. Simple and readily available tert-butyl nitrite (TBN) was employed as the NO source.

Dehydrogenative N‐Incorporation: A Direct Approach to Quinoxaline N‐Oxides under Mild Conditions

AbstractAn efficient method for the synthesis of quinoxaline N‐oxides proceeds by the dehydrogenative N‐incorporation of simple imines by C(sp2)H and C(sp3)H bond functionalization. The overall transformation involves the cleavage of three CH bonds. The reaction is easily handled and proceeds under mild conditions. Simple and readily available tert‐butyl nitrite (TBN) was employed as the NO source.

Synthesis of tetra-substituted imidazoles and 2-imidazolines by Ni(0)-catalyzed dehydrogenation of benzylic-type imines.

Ni(0)-catalyzed dehydrogenation of benzylic-type imines was performed to yield asymmetrical tetra-substituted imidazoles and 2-imidazolines. This was achieved with a single operational step while maintaining good selectivity and atom economy. The catalytic system shows low to moderate tolerance for fluoro-, trifluoromethyl-, methyl-, and methoxy-substituted benzylic-type imines. In addition, the substitution pattern at the N-heterocyclic products was easily controlled by the appropriate selection of R-groups in the starting organic substrates. Based on experimental observations, we propose a reaction mechanism in which benzylic C(sp(3))-H bond activation and insertion steps play pivotal roles in this nickel-catalyzed organic transformation.

An Efficient Synthesis of Substituted Quinolines via Indium(III) Chloride Catalyzed Reaction of Imines with Alkynes

An efficient synthetic method for the preparation of quinolines through indium(III) chloride-catalyzed tandem addition-cyclization-oxidation reactions of imines with alkynes was developed. The processes can provide a diverse range of quinoline derivatives in good yields from simple imines and alkynes.

Sequential Catalysis for the Production of Sterically Hindered Amines: Ru(II)-Catalyzed C–H Bond Activation and Hydrosilylation of Imines

Sequential ruthenium(II) catalyzed reactions for the production of secondary amines from simple imines are reported. They involve Ru(II)-acetate based catalytic systems for C–H Bond activation/diarylation of simple imines with aryl bromides followed by [RuCl2(arene)]2 hydrosilylation of diarylated imines. The direct diarylation of aldimines can be profitably produced by Ru(II) catalytic systems in the presence of both acetate and PPh3 ligands. By contrast, PPh3 additive disfavors diarylation of ketimines that is achieved with [Ru(OAc)2(p-cymene)] alone. The catalytic hydrosilylation of the resulting imines was simply performed with H2SiPh2 in the presence of [RuCl2(arene)]2 catalyst at room temperature leading to overall yield of 70–86% of secondary amines

ChemInform Abstract: Electrochemical Allylation Reactions of Simple Imines in Aqueous Solution Mediated by Nanoscale Zinc Architectures.

AbstractDeposited zinc(0) powder with nanoscale hierarchitectures play an important role in the electrochemical reaction of imines with allylic bromides, benzyl bromides, and alkyl iodides in aqueous solution.

Palladium‐Catalyzed Asymmetric Hydrogenation of Simple Ketimines Using a Brønsted Acid as Activator

AbstractUsing a catalytic amount of a Brønsted acid as activator of simple imines, the highly enantioselective homogeneous palladium‐catalyzed asymmetric hydrogenation of simple ketimines was successfully developed with up to 95% ee.

Electrochemical Allylation Reactions of Simple Imines in Aqueous Solution Mediated by Nanoscale Zinc Architectures

Zink, elektrochemisch aufbereitet: Bei den Titelreaktionen, die in wässriger Lösung an einem Paar Zinkelektroden ausgeführt wurden, gibt es Anzeichen für einen Einfluss der Oberflächenmorphologie an den Elektroden: Die Abscheidung von nanostrukturiertem Zinkpulver ergab sehr hohe Aktivitäten. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Electrochemical Allylation Reactions of Simple Imines in Aqueous Solution Mediated by Nanoscale Zinc Architectures

Deposited zinc(0) powder with nanoscale hierarchitectures play an important role in the electrochemical reaction of imines with allylic bromides, benzyl bromides, and alkyl iodides in aqueous solution.