Search

[Display omitted] • Versatile Synthesis of Homoallylamines: This study presents efficient methods for the synthesis of homoallylamines, which are valuable precursors in the formation of bioactive N -heterocycles, such as pyrrolidines and β-lactams. • Regioselective Allylation: The research demonstrates the regioselective allylation of aldimines with allyl metal reagents under sonochemical Barbier-type reaction conditions and AlCl3 catalysis, achieving both α-adduct and γ-adduct formations. • High Regio- and Stereoselectivity: Optimized reaction conditions lead to high regio- and stereoselectivity, with ultrasonic-mediated conditions favoring α-adducts and AlCl3 catalysis promoting γ-adducts. • Substrate Scope and Functional Group Compatibility: The methods exhibit broad substrate scope, accommodating various aldimines with different substituents, including phenyl, tosyl, and heteroaromatic groups, yielding products in moderate to good yields with excellent regioselectivity. • Mechanistic Insights: Proposed mechanisms for both the sonochemical and AlCl3-catalyzed processes explain the observed regioselectivity and diastereoselectivity, highlighting the role of zinc activation and Lewis acid catalysis in facilitating the reactions. The allylation reaction of aldimines with allyl metal reagents is an important synthetic method for the preparation of homoallylamines. Therefore, we wish to report a highly regioselective and stereoselective allylation reaction under sonochemical Barbier-type reaction conditions. The high yields of regioselective α-adducts were achieved by reacting cinnamyl bromide, zinc, 1,2-dibromoethane, and aldimine in THF under sonochemical Barbier-type conditions. Highly regioselective and stereoselective allylation reactions were also achieved under Lewis acid-promoted Barbier-type reaction conditions. [ABSTRACT FROM AUTHOR]

A convenient procedure of synthesis of N-carbamoyl-protected propargylic amines substituted with a cyclopropyl group from α-amido sulfones and cyclopropylacetylene is described. The reaction is catalyzed by a chiral BINOL-type zinc complex and provides the corresponding products in good yields and enantioselectivities. [ABSTRACT FROM AUTHOR]

[Display omitted] N -Benzyl aldimines react with arylacetylenes in the presence of ButOK/DMSO superbase system to afford 2,3,5-triaryl-1-pyrrolines as two tautomers with 1,2- and 1,5-location of the double bond, both being the trans -diastereomers. This version of the C=N bond ethynylation differs from the previous one with N- benzyl ketimines. The oxidation of the pyrroline tautomeric mixtures without their isolation gives 2,3,5-triaryl-1 H -pyrroles. [ABSTRACT FROM AUTHOR]

Copyright of Nachrichten aus der Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Here we report for the first time the regio‐ and diastereoselective [3+2] annulation of a wide range of aliphatic aldimines with alkenes via the activation of an unactivated β‐C(sp3)−H bond by half‐sandwich scandium catalysts. This protocol offers a straightforward and atom‐efficient route for the synthesis of a new family of multi‐substituted aminocyclopentane derivatives from easily accessible aliphatic aldimines and alkenes. The annulation of aldimines with styrenes exclusively afforded the 5‐aryl‐trans‐substituted 1‐aminocyclopentane derivatives with excellent diastereoselectivity through the 2,1‐insertion of a styrene unit. The annulation of aldimines with aliphatic alkenes selectively gave the 4‐alkyl‐trans‐substituted 1‐aminocyclopentane products in a 1,2‐insertion fashion. A catalytic amount of an appropriate amine such as adamantylamine (AdNH2) or dibenzylamine (Bn2NH) showed significant effects on the catalyst activity and stereoselectivity. [ABSTRACT FROM AUTHOR]

The commercially available and bench‐stable Co(acac)2 ligated with bis[(2‐diphenylphosphino)phenyl] ether (dpephos) was employed for selective room temperature hydroboration of nitro compounds with HBPin (TOF up to 4615 h−1), tolerating halide, hydroxy, amino, ether, ester, lactone, amide and heteroaromatic functionalities. These reactions offered a direct access to a variety of N‐borylamines RN(H)BPin, which were in situ treated with aldehydes and carboxylic acids to produce a series of aldimines and secondary carboxamides without the need for dehydrating and/or coupling reagents. Combination of these transformations in a sequential one‐pot manner allowed for direct and selective synthesis of aldimines and secondary carboxamides from readily available and inexpensive nitro compounds. [ABSTRACT FROM AUTHOR]

By using a chiral directing group, an asymmetric rhodium(III)‐catalyzed C−H bond addition to aldimines followed by intramolecular cyclization to form chiral isoindolinones has been achieved (up to 68 % yield, up to 93 % ee). A three‐component variant that resembles Mannich reaction was also realized (41 % yield, 83 % ee). Product elaborations and preliminary mechanistic studies were described. [ABSTRACT FROM AUTHOR]

A user-friendly, energy efficient method of synthesizing N-sulfonyl aldimines at room temperature (25-28°C) from readily available and inexpensive reagents has been developed. The method employs ultrasonication from common laboratory ultrasonic cleaner to mediate the reaction. FeCl3 as catalyst and molecular sieves as water scavenger have produced excellent yields of aldimines with short reaction time. The reaction set-up does not require inert atmosphere or anhydrous solvent thereby saving resources and time. The easily scalable method works well for the condensation of aromatic non-enolizable aldehydes and sulfonamides. [ABSTRACT FROM AUTHOR]

Palladium catalysts supported on acidic fluorinated magnesium hydroxide Pd/MgF2−x(OH)x were prepared through precipitation or impregnation methods. Applications to the hydrogenation of various aldimines and ketimines resulted in good catalytic activities at mild temperatures using one atmosphere of hydrogen. Quinolines, pyridines and other N-heterocycles were successfully hydrogenated at higher temperature and hydrogen pressure using low palladium loadings and without the use of any acid additive. Such reactivity trend confirmed the positive effect of the Brønsted and Lewis acid sites from the fluorinated magnesium hydroxide support resulting in the effective pre-activation of N-heterocycle substrates and therefore in the good catalytic activity of the palladium nanoparticles during the hydrogenations. As demonstrated in the hydrogenation of imines, the catalyst was recycled up to 10 times without either loss of activity or palladium leaching. [ABSTRACT FROM AUTHOR]

Mannich reactions are one among the most investigated reactions in organic chemistry. Recently, silver‐catalyzed Mannich reactions have gained much recognition owing to the efficiency of silver catalysis. The review encompasses the various strategies towards silver‐catalyzed Mannich reactions and cases literature up to 2021. [ABSTRACT FROM AUTHOR]

Anti‐Markovnikov addition of anilines to aliphatic terminal alkynes proceeded using an 8‐quinolinolato rhodium/phosphine catalyst system. The use of a strong organic base, 1,1,3,3,–tetramethylguanidine, in the catalyst system enabled the formation of the aldimine products. Substrates with various functional groups including polar groups such as a phenolic hydroxy group are applicable to the hydroamination. [ABSTRACT FROM AUTHOR]

The reactions of N-trimethylsilyl derivatives of α- and β-amino acid esters with sulfur tetrafluoride lead to the formation of the corresponding difluorides of imidosulfurous acids F2S=N-X (X = α or β-amino acid residue). The reaction products of difluorides with N-trimethylsilylmorpholine are ketimines or aldimines of new types, containing an imine fragment =N-S-NR2 at the α- or β-carbon atom of the amino acid. The reactions of difluorides F2S=N-X with N-trimethylsilyl esters of α- and β-amino acids lead to the formation previously unknown derivatives of sulfur diimides with amino acid residues at the nitrogen atoms of the group -N=S=N-. [ABSTRACT FROM AUTHOR]

Through-bond conjugation (TBC) and/or through-space conjugation (TSC) determine the photophysical properties of organic luminescent compounds. No systematic studies have been carried out to understand the transition from aromatic TBC to non-aromatic TSC on the photoluminescence of organic luminescent compounds. In this work, a series of small aromatic and aliphatic aldimines were synthesized. For the aromatic imines, surprisingly, N,1-diphenylmethanimine with the highest TBC is non-emissive, while N-benzyl-1-phenylmethanimine and N-cyclohexyl-1-phenylmethanimine emit bright fluorescence in aggregate states. The aliphatic imines are all emissive, and their maximum emission wavelength decreases while the quantum yield increases with a decrease in steric hindrance. The imines show concentration-dependent and excitation-dependent emissions. Theoretical calculations show that the TBC extents in the aromatic imines are not strong enough to induce photoluminescence in a single molecule state, while the intermolecular TSC becomes dominant for the fluorescence emissions of both aromatic and aliphatic imines in aggregate states, and the configurations and spatial conformations of the molecules in aggregate states play a key role in the formation of effective TSC. This study provides an understanding of how chemical and spatial structures affect the formation of TBC and TSC and their functions on the photoluminescence of organic luminescent materials.

We demonstrate here conclusively that the variational multiconfiguration Gaussian (vMCG) method converges to the grid based full quantum dynamics multiconfiguration time-dependent Hartree result for a tunnelling problem in many dimensions, using the intramolecular proton transfer in salicylaldimine as a model system. The 13-dimensional model potential energy surface was obtained from Hartree Fock energies with the 6-31G* basis set and the expectation value of the flux operator along the transition mode was used as a benchmark characteristic. As well as showing excellent convergence of the vMCG method on the model surface using a local harmonic approximation and a moderate number of basis functions, we show that the direct dynamics version of the vMCG also performs very well, usually needs the same number of Gaussians to converge, and converges to exact results if those are obtained on an accurately fitted surface. Finally, we make an important observation that the width of the Gaussian basis functions must be chosen very carefully to obtain accurate results with the use of the frozen-width approximation. [ABSTRACT FROM AUTHOR]

Exploiting anion–π interactions in catalyst design is a fascinating direction to develop new and fundamental catalysis. For the appealing yet flexible π‐face activation, can two or more π‐acidic surfaces be manipulated for cooperative activation to achieve efficient transformation and particularly selectivity control is highly desirable. Here, we demonstrate a supramolecular π‐catalysis strategy by establishing cooperative π‐face activation in a confined electron‐deficient cage cavity. The catalysts have a triazine based prism‐like cage core and pendant chiral base sites. Only 2 mol % of cage catalyst efficiently catalyzed the decarboxylate Mannich reactions of sulfamate‐headed cyclic aldimines and a series of malonic acid half thioesters in nearly quantitative yields and up to 97 % ee, enabling an unprecedent organocatalytic approach. The supramolecular π‐cavity is essential in harnessing cooperative anion–π interactions for the efficient activation and excellent selectivity control. [ABSTRACT FROM AUTHOR]

New derivatives of FAM (ferrocenyl aziridinyl methanol) ligands NFAM1–4 (naphthyl ferrocenyl aziridinyl methanol) and CFAM1–4 (cyclohexyl ferrocenyl aziridinyl methanol) were synthesized to form a small ligand library and used as chiral catalysts with AgOAc for the asymmetric synthesis of heteroaryl‐substituted pyrrolidines by the 1,3‐dipolar cycloaddition (1,3‐DC) reaction of azomethine ylides. 2‐Thienyl, 2‐furyl, 2‐, 3‐, and 4‐pyridyl aldimines were prepared and used with N‐methylmaleimide, dimethyl maleate, tert‐butyl acrylate, methyl acrylate, and acrylonitrile to form the corresponding heteroaryl‐substituted pyrrolidines. 1,3‐DC reactions yielded the expected cycloadducts in up to 89% yield and up to 76% ee that could be increased up to 95% ee upon crystallization. New chiral ligands NFAM1–4 and CFAM1–4 were fully characterized, and their absolute stereochemistry was determined by single‐crystal X‐ray analysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nickel disulfide decorated CdS nanosheets (NiS 2 /CdS) are synthesized. • NiS 2 can serve as the active sites for hydrogen evolution reaction and dehydrogenation reaction. • The integrated photocatalytic redox cycles for H 2 production and imine synthesis are achieved on NiS 2 /CdS. Photocatalytic hydrogen (H 2) evolution integrated with selective oxidation to produce fine chemicals is a promising strategy for solar energy conversion and storage; however, the efficiency of such coupled photocatalytic redox cycles is greatly limited by the poor surface kinetics of hydrogen evolution reaction (HER) and/or dehydrogenation reaction (DHR) on heterogenous photocatalysts. Herein, we demonstrate that the immobilization of ultrafine nickel disulfide (NiS 2) nanoparticles on CdS nanosheets (NiS 2 /CdS) is a simple yet efficient approach to kinetic improve the surface redox reactions for H 2 production and dehydrogenative coupling of amines to imines. The NiS 2 nanoparticles loaded on CdS not only function as the HER active sites to speed up charge separation and to boost H 2 release, but also enhance the adsorption of amines to facilitate the dissociation of C-H and N-H bonds to form aldimines intermediates, which are readily coupled with other amines to afford a high selectivity toward imine synthesis. Benefiting from such unique bifunctional catalytic behavior of NiS 2 in proton (H+) reduction and substrate activation, NiS 2 /CdS exhibits a remarkable enhanced photocatalytic performance toward simultaneous production of H 2 and imines. The apparent quantum efficiency (AQE) at 420 nm is calculated to be 54.7%. This strategy using bifunctional cocatalysts to kinetic improve the surface redox reactions will have broad implications in the development of high-performance photocatalysts for integrated production of solar hydrogen and value-added solar chemicals. [ABSTRACT FROM AUTHOR]

Sulphonamides and N‐sulphonyl ketimines/aldimines have turned out to be versatile motifs in the field of synthetic and medicinal chemistry. The field of C−H activation/functionalization flourished remarkably due to their synthetic applicability and directing group plays a remarkable role to achieve regioselectivity in these reactions. The current review summarizes recent tactics by utilizing sulphonamides and N‐sulphonyl ketimines/aldimines as directing groups for C−H activation or functionalization. As a directing group, they also facilitate site selectivity and late‐stage functionalization of drug molecules in order to construct complex scaffolds of therapeutic importance by C−H activation. [ABSTRACT FROM AUTHOR]

Two Schiff base donor ligands (aldimines) were used to prepare four transition metal complexes of Cu(II) and Zn(II) by treating 2-nitroaniline and salicylaldehyde to form the Schiff base ligand 2[(2-nitrophenylimino) methyl] phenol (L1) and 4-nitroaniline and salicylaldehyde to form 2-[(4-nitrophenylimino)]methyl]phenol (the L2 counterpart). The processes were accomplished using a microwave oven assisted reaction regulated at 1000C for 30 min. Characterization was carried out on the basis of physical properties elemental analysis, FTIR, 1H-NMR and 13C-NMR spectroscopy, electronic spectral and mole ratio method. Results from the FTIR spectra of the ligands and corresponding complexes showed that the ligands L1 and L2 displayed a bidentate character with coordination via the nitrogen and oxygen atoms. The 1H-NMR and 13C-NMR data of L1 and L2 confirmed the formation of the complexes of Cu(II) and Zn(II) showing that the probable coordination geometries of Cu(II) and Zn(II) are octahedral. The complexes were found to be non electrolytes in alcohol. The nematicidal activity studies implied that the ligands and their metal complexes showed promising nematicidal ability with the metal complexes showing comparatively higher inhibiting ability than the free ligands against the root knot nematode Meloidogyne arenaria present in the crop Arachis Hypogea. [ABSTRACT FROM AUTHOR]

We report the synthesis of β‐lactams from α‐ketoacylsilanes and imines, which proceeds via a formal [2+2] photochemical cycloaddition with in situ generation of siloxyketene. This mild and operationally simple reaction proceeds in an atom‐economic fashion with broad substrate scope, including aldimines, ketimines, hydrazones, and fused nitrogen heterocycles, affording a variety of important β‐lactams with satisfactory diastereoselectivities in most cases. This reaction also features good functional‐group tolerance, facile scalability and product diversification. Experimental and computational studies suggest that α‐ketoacylsilanes can serve as photochemical precursors by engaging in a 1,3 silicon shift to the distal carbonyl group. [ABSTRACT FROM AUTHOR]

Azomethine imines constitute a versatile class of dipoles that are being increasingly used for the synthesis of biologically relevant heterocycles. This review details the various reactions reported in the literature from 2015–2020 involving acyclic, C,N-cyclic and N,N-cyclic azomethine imines as well as any reported mechanistic aspects of the reactions. [ABSTRACT FROM AUTHOR]

The intramolecular ligand hydroxylation of a series of copper(I) imine complexes during their reaction with dioxygen had been systematically studied. The so‐called clip‐and‐cleave concept offers a facile way to oxygenate aldehydes or ketones. A copper(I) complex for example, with an imine ligand derived from an ethylenediamine derivative and cyclohexanone was oxidized. Decomposing the complex after the reaction with hydrochloric acid showed a 50 % conversion of the cyclohexanone to 2‐hydroxycylohexanone. Depending on the ligand system, three different reaction pathways have been identified that can cause hydroxylation reactions. While the radical based mechanisms are more difficult to identify, the reactions that go through a copper bis(μ‐oxido) complex as active species can be analyzed by low temperature stopped‐flow techniques. In an ideal case the formation and decomposition of this reactive intermediate can be spectroscopically observed. It was shown that this depends strongly on the ligand system: steric effects, chelate ring size and coordination number play an important role for the mechanism and the outcome of the reaction. [ABSTRACT FROM AUTHOR]

An efficient stereocontrolled preparation of 2-substituted pyrrolidines and 5-substituted indolizidin-7-ones, by using chiral N - tert -butanesulfinyl imines derived from 4-halobutanal as starting materials, is detailed. Addition of Grignard reagents and a decarboxylative Mannich- reaction with β-keto acids involving these chiral imines proceeded with high diastereoselectivity. The synthesis of the pyrrolidinic alkaloids (–)-bgugaine, (+)-villatamine B, (–)-norhygrine, trans -dendrochrysanine, and (–)-ruspolinone demonstrated the utility of this methodology. [ABSTRACT FROM AUTHOR]

Optimizing C=N bond formation and C/N component exchange has major significance in Dynamic Covalent Chemistry (DCC). Imine and hydrazone generation from their aldehyde, amine and hydrazine components showed large accelerations in presence of AgOTf or Zn(OTf)2, up to 104 for the Zn(II)‐(p‐anisidine)imine complex. Zn(OTf)2 and auxiliary p‐anisidine together accelerated 630 times the formation of the Zn(II)‐hydrazone complex, revealing a strong synergistic effect, traced to very fast initial formation of the reactive Zn(II)‐imine complex presenting a C=N bond metallo‐activated towards reaction with the hydrazine component. Reactions involving more entities showed kinetically faster and thermodynamically simpler outputs due to dynamic competition within a mixture of higher complexity. Catalytic amounts of metal salts and auxiliary amine gave similar marked rate accelerations and turnover, indicating true catalysis. The synergistic effect achieved by combining metallo‐ and organo‐catalysis points to a powerful co‐catalysis strategy of bond‐formation in DCC through interconnected chemical transformations. [ABSTRACT FROM AUTHOR]

Recently, diimine Re(I) tricarbonyl complexes have attracted great interest due to their promising cytotoxic effects. Here, we compare the cytotoxicity and cellular uptake of two Re(I) compounds fac-[(Re(CO)3(bpy)(H2O)](CF3SO3) (1) and Na(fac-[(Re(CO)3(bpy)(S2O3)])·H2O (bpy = 2,2′-bipyridine) (2). The Re-thiosulfate complex in 2 was characterized in two solvated crystal structures {Na(fac-[Re(CO)3(bpy)(S2O3)])·1.75H2O·C2H5OH}4 (2 + 0.75H2O + C2H5OH)4 and (fac-[Re(CO)3(bpy)(H2O)]) (fac-[Re(CO)3(bpy)(S2O3)])·4H2O (3). The cytotoxicity of 1 and 2 was tested in the MDA-MB-231 breast cancer cell line and compared with that of cisplatin. The cellular localization of the Re(I) complexes was investigated using synchrotron-based X-ray fluorescence microscopy (XFM). The results show that replacement of the aqua ligand with thiosulfate renders the complex less toxic most likely by distrupting its cellular entry. Therefore, thiosulfate could potentially have a similar chemoprotective effect against diimine fac-Re(CO)3 complexes as it has against cisplatin. [ABSTRACT FROM AUTHOR]

The mixed ligand copper(II) complexes [Cu(terpy)(mq)]ClO4 (1) and [Cu(phen)(mq)]ClO4 (2), in which terpy = 2,2′:6′,2′′-terpyridine, phen = 1,10-phenanthroline and H(mq) = 2-methyl-8-hydroxyquinoline, have been synthesized. The crystal structure of 1 discloses a distorted square-pyramidal geometry (τ = 0.16). The coordination geometry around Cu(II) in the density functional theory optimized structures of 1 and 2 has been assessed and found to show a distorted square pyramidal and square planar respectively. They exhibit a ligand field band and their frozen solution EPR spectra are axial (g‖ > g⊥ > 2.0) suggesting a square-based geometry around Cu(II) with a dx2−y2 ground state. The complexes interacted with calf thymus (CT) DNA and were found to be groove binding, as determined by various spectral and redox techniques. Interestingly, 2 cleaves supercoiled φX174 DNA without a reductant while 1 cleaves with the reductant. Furthermore, the quenching of the tryptophan emission of BSA in the presence of the complexes is static. The binding is mainly entropy-driven and hydrophobic forces played a major role. The DNA and protein binding affinity and the DNA cleavage activity is in the order 2 > 1, and the higher DNA and protein binding affinity and DNA cleavage activity of 2 illustrates the strong involvement of the 2-methyl group on the mq ring in the hydrophobic interaction with the DNA and protein. Furthermore, cytotoxicity studies of 1 and 2 on MCF7 and SiHa cell lines show that the IC50 values are lower than those of cisplatin and illustrate a lower cytotoxicity against the Jurkat T4 normal cell line. AO/EB and Hoechst 33258 staining assays reveal the higher induction of apoptosis for 1 and 2. The alkaline single-cell electrophoresis (comet assay) indicates that the complexes induce DNA fragmentation, which provides additional proof of the apoptosis. [ABSTRACT FROM AUTHOR]

1,2-Dihydropyridines are valuable and reactive synthons, and particularly useful precursors to synthesize piperidines and pyridines that are among the most common structural components of pharmaceuticals. However, the catalytic enantioselective synthesis of structurally diverse 1,2-dihydropyridines is limited to enantioselective addition of nucleophiles to activated pyridines. Here, we report a modular organocatalytic Mannich/Wittig/cycloisomerization sequence as a flexible strategy to access chiral 1,2-dihydropyridines from N-Boc aldimines, aldehydes, and phosphoranes, using a chiral amine catalyst. The key step in this protocol, cycloisomerization of chiral N-Boc δ-amino α,β-unsaturated ketones recycles the waste to improve the yield. Specifically, recycling by-product water from imine formation to gradually release the true catalyst HCl via hydrolysis of SiCl4, whilst maintaining a low concentration of HCl to suppress side reactions, and reusing waste Ph3PO from the Wittig step to modulate the acidity of HCl. This approach allows facile access to enantioenriched 2-substituted, 2,3- or 2,6-cis-disubstituted, and 2,3,6-cis-trisubstituted piperidines. 1,2-Dihydropyridines are valuable precursors for the synthesis of biologically relevant piperidines and pyridines, but the methods for their synthesis are underdeveloped. Here, the authors report a modular organocatalytic Mannich/Wittig/cycloisomerization sequence to access chiral 1,2-dihydropyridines from N-Boc aldimines, aldehydes and phosphoranes, using a chiral amine catalyst. [ABSTRACT FROM AUTHOR]

The use of functionalized aldimines has been demonstrated as newly structural 1,4‐dipole precursors under carbene catalysis. More importantly, enantiodivergent organocatalysis has been successfully developed using carbene catalysts with the same absolute configuration, leading to both (R)‐ and (S)‐ enantiomers of six‐membered heterocycles with quaternary carbon centers. This strategy features a broad substrate scope, mild reaction conditions, and good enantiomeric ratio. DFT calculation results indicated that hydrogen bond C−H⋅⋅⋅F interactions between the catalyst and substrate are the key factors for controlling and even switching the enantioselectivity. These new 1,4‐dipoles can also react with isatin and its imines under carbene catalysis, allowing for access to the spiro oxindoles with excellent enantiomeric ratios. [ABSTRACT FROM AUTHOR]

A new mode of carbene‐catalyzed heteroatom activation and asymmetric reactions is disclosed. The reaction starts with addition of a carbene catalyst to a (benz)imidazole‐derived aldimine substrate. Subsequent oxidation and proton transfer lead to the formation of a catalyst‐bound triaza‐diene as the key intermediate, in which the nitrogen atom at a site remote to the catalyst‐substrate bond is activated. This unusual triaza‐diene intermediate then undergoes highly enantioselective reactions with activated ketones through a concerted asynchronous pathway, as supported by mechanistic studies and preliminary density function theory calculation. [ABSTRACT FROM AUTHOR]

α‐Amino acids are of fundamental importance for life. Both natural and artificial α‐amino acids also play a crucial role for pharmaceutical purposes. The catalytic asymmetric Strecker reaction still provides one of the most attractive strategies to prepare scalemic α‐amino acids. Here we disclose a new concept for Strecker reactions, in which an achiral Brønsted base cooperates with a Lewis acid and an aprotic ammonium salt, which are both arranged in the same chiral catalyst entity. The described method could successfully address various long‐standing practical issues of this reaction type. The major practical advantages are that (1) the N‐protecting group is readily removable, (2) acetone cyanohydrin is attractive as cyanation reagent in terms of atom economy and cost efficiency, (3) an excess of the cyanation reagent is not necessary, (4) the new method does not require additives and (5) is performed at ambient temperature. [ABSTRACT FROM AUTHOR]

The first regio‐, diastereo‐, and enantioselective direct Mannich reaction of β,γ,‐unsaturated ketones with benzoxazinone cyclic imines was enabled by Lewis acid/Brønsted base cooperative catalysis. The dinuclear zinc complex catalyzed the reaction of a broad range of β,γ‐unsaturated ketones to proceed at the α‐site exclusively, leading to corresponding adducts with two consecutive tertiary carbon stereocenters in diastereomeric ratios of up to >20:1 and enantioselectivities generally in the 90–99 % ee range. These products were used as general intermediates in the synthesis of multisubstituted cyclocanalines, tetrahydro pyridazinones, and 4H‐furo[2,3‐b][1,4]benzoxazine derivatives. [ABSTRACT FROM AUTHOR]

The first successful enantioselective hydrosilylation of cyclic imines promoted by a chiral zinc complex is reported. In situ generated zinc‐ProPhenol complex with silane afforded pharmaceutically relevant enantioenriched 2‐aryl‐substituted pyrrolidines in high yields and with excellent enantioselectivities (up to 99% ee). The synthetic utility of presented methodology is demonstrated in an efficient synthesis of the corresponding chiral cyclic amines, being pharmaceutical drug precursors to the Aticaprant and Larotrectinib. [ABSTRACT FROM AUTHOR]

Despite the widespread applications of C–H functionalization, controlling site selectivity remains a significant challenge. Covalently attached directing groups (DGs) served as ancillary ligands to ensure ortho-, meta- and para-C–H functionalization over the last two decades. These covalently linked DGs necessitate two extra steps for a single C–H functionalization: introduction of DG prior to C–H activation and removal of DG post-functionalization. Here we report a temporary directing group (TDG) for meta-C–H functionalization via reversible imine formation. By overruling facile ortho-C–H bond activation by imine-N atom, a suitably designed pyrimidine-based TDG successfully delivered selective meta-C–C bond formation. Application of this temporary directing group strategy for streamlining the synthesis of complex organic molecules without any necessary pre-functionalization at the meta position has been explored. Site-selective C–H functionalization still faces some challenges, such as the introduction and removal of an appropriate directing group. Here, the authors introduce a temporary directing group for selective meta-C–H functionalization of 2-arylbenzaldehydes via reversible imine formation. [ABSTRACT FROM AUTHOR]

Seven homo- and hetero-bimetallic macromolecular complexes (BMCs) were prepared via an in-situ multi-step complexation reaction of CuII, NiII and FeIII metal centers with imine- oxime π-conjugated ditropic spacer (1,4-phenylene-bis(2,3-butanedeimineoxime, L2−). The structures of the obtained [M-L2-M]x, [M'-L2-M']x, [M-L2-M']x and their μ-oxo-[M-L2-Fe]x BMCs (M = CuII, NiII; M' = FeIII) were elucidated using different spectroscopic (UV–Vis, FT-IR), powder X-ray diffraction (p-XRD) and microscopic (SEM) techniques. The SEM images indicate that the obtained BMCs exhibit nano/micro globular and rod-like textures. The electrical and magnetic characteristics of the obtained BMCs can be described as magneto-semiconducting materials. The structural, electrical, and magnetic properties inherited in the prepared regime demonstrate that the examined semiconducting π-spacer has clear ability to semi-conduct electron transport and delocalize spin leading to antiferromagnetic coupling, thus offering a favorable magnetic exchange pathway between the paramagnetic metal sites. However, ferromagnetic enhancement is observed in the μ-oxo-[M-L2-Fe]x BMCs where the μ-oxo-bridge overplays the role of the π-spacer. A magnetic responsive thin film was conveniently obtained by solvent casting of the μ-oxo-[Ni-L2-Fe]x BMC in a transparent poly(methamethylacrylate) matrix. [ABSTRACT FROM AUTHOR]

The utility and selectivity of the newly synthesized dinuclear arene Ru(II) complex were demonstrated towards the synthesis of imines from coupling of alcohols and amines in the aerobic condition. Analytical and various spectral methods have been used to establish the unprecedented formation of the new thiolato‐bridged dinuclear ruthenium complex. The molecular structure of the titled complex was evidenced with aid of X‐ray crystallographic technique. A wide range of imines were obtained in good‐to‐excellent yields up to 98% and water as the by‐product through an acceptorless dehydrogenative coupling of alcohols with amines. The catalytic reaction operated a concise atom economical without any oxidant with 1 mol% of the catalyst load. Further, the role of base, solvent and catalyst loading of the coupling reaction has been investigated. A plausible mechanism has been described and was found to proceed via the formation of an aldehyde intermediate. Short synthesis of antibacterial drug N‐(salicylidene)‐2‐hydroxyaniline illustrated the utility of the present protocol. [ABSTRACT FROM AUTHOR]

Ba metal was activated by evaporation and cocondensation with heptane. This black powder is a highly active hydrogenation catalyst for the reduction of a variety of unactivated (non‐conjugated) mono‐, di‐ and tri‐substituted alkenes, tetraphenylethylene, benzene, a number of polycyclic aromatic hydrocarbons, aldimines, ketimines and various pyridines. The performance of metallic Ba in hydrogenation catalysis tops that of the hitherto most active molecular group 2 metal catalysts. Depending on the substrate, two different catalytic cycles are proposed. A: a classical metal hydride cycle and B: the Ba metal cycle. The latter is proposed for substrates that are easily reduced by Ba0, that is, conjugated alkenes, alkynes, annulated rings, imines and pyridines. In addition, a mechanism in which Ba0 and BaH2 are both essential is discussed. DFT calculations on benzene hydrogenation with a simple model system (Ba/BaH2) confirm that the presence of metallic Ba has an accelerating effect. [ABSTRACT FROM AUTHOR]

We firstly describe a silver-catalyzed direct C–H functionalization of cyclic aldimines with cyclopropanols and cyclobutanols via a radical-mediated C–C bond cleavage strategy. The desired products were generated in decent yields with wide substrate scope under mild reaction conditions. In addition, a gram-scale reaction and synthetic transformation of the product were performed. [ABSTRACT FROM AUTHOR]

The Mannich reaction is a multicomponent reaction resulting in aminoalkylation of an acidic proton placed next to a carbonyl functional group. It involves an appropriate carbonyl compound, such as formaldehyde and a primary or secondary amine or ammonia. The final product is a β‐amino‐carbonyl compound known as a Mannich base. Reactions between aldimines and α‐methylene carbonyls are also considered as Mannich reaction since these imines are generated from the reaction of amines and aldehydes. It comprises the reaction of primary or secondary amines or ammonia, formaldehyde and appropriate α‐CH‐acidic compounds (nucleophiles) such as carbonyl compounds having α‐CH‐acidic, nitriles, acetylenes, aliphatic nitro compounds, α‐alkyl‐pyridines or imines. Owing to the development of asymmetric organocatalysis, reports on asymmetric Mannich reaction have been drastically increased. The asymmetric Mannich reaction offers access to enantioenriched β‐amino ketones or β‐amino aldehydes, which are present as a scaffold in several natural products. Organocatalysts have been developed not only as a supplement to metal‐catalyzed reactions or to biocatalysis, but nowadays, they are extensively used for the synthesis of various optically pure compounds that could not be achieved via metal‐ or biocatalyzed reactions. In this review, we try to update the advances in organocatalyzed asymmetric Mannich reactions, covering the recent advances of the subject from 2008 to date. [ABSTRACT FROM AUTHOR]

Because molecular iodine and hydrosilanes are stable to both air and moisture, reactions using these reagents are easy to operate and require mild reaction conditions. Molecular iodine and a hydrosilane were used to reduce N -sulfonyl aldimines to the corresponding N -alkylsulfonamides. This transformation is a practical method for the synthesis of N -alkylsulfonamides. [ABSTRACT FROM AUTHOR]

Herein, we report our strategy to develop the efficient chemosensor and real-time monitoring technique for cyanuric chloride (TCT) detection. A luminescent macrocyclic mononuclear Sm(III) complex Sm - 2 k bearing with two dynamic imine bonds has been constructed via the template synthesis between dialdehyde H 2 Q k and matched diamine 1,2-bis(2-aminoethoxy)ethane. Sensing experiments reveal that complex Sm - 2 k exhibits the turn-off fluorescent and colorimetric response for TCT in CH 3 OH. It is especially encouraging that this optical sensing process is not only rapid within 60 s but also high-efficient in the presence of TCT analogues as well as sensitive with the low limit of detection (LOD, 1.74 μM) and wide linear sensing range. Mechanism studies demonstrate that TCT sensing is mainly based on the imine bond transformation of probe Sm - 2 k , which is due to the increased acidity induced by TCT. Meanwhile, a smartphone-based analytical method was developed to make complex Sm - 2 k accessible for the real-time TCT detection by RGB value outputs. It is believed that this work can shed some constructive lights on design of chemosensors and convenient detection technique for highly reactive analytes. Image 1 • A Sm(III) complex Sm - 2 k with two imine bonds is constructed by template synthesis. • Sm - 2 k shows turn-off fluorescent and colorimetric responses for cyanuric chloride. • Efficient sensing involves in imine bond transformation induced by HCl in CH 3 OH. • Smartphone-based analysis provides a real-time and convenient detection method. [ABSTRACT FROM AUTHOR]

Silica‐supported ammonium (R)‐BINSate catalysts for the enantio‐ and diastereoselective Friedel–Crafts‐type double aminoalkylation of N‐benzyl‐ or N‐methylpyrrole with aldimines were developed. The present heterogeneous catalysts showed high catalytic activity compared to our previous homogeneous (R)‐BINSA ammonium catalysts, which were effective for single aminoalkylation. Simple aldimines could be used, and the corresponding pyrrole‐derived chiral C2‐symmetric triamines were obtained in the dl‐form with good to extremely high enantioselectivities. The heterogeneous catalyst could be easily recovered and reused three times without any loss of catalytic activity or enantiocontrol. An XPS analysis supported precise preparation of the catalysts in situ and with good quality after recycling three times. From the perspective of modern green chemistry with fine asymmetric organocatalysis, the development of such chiral strong Brønsted acid catalysts might be useful for both laboratory and industrial applications. [ABSTRACT FROM AUTHOR]

Several energetic salts of the 5-amino-3-methyl-1,2,3-oxadiazolium cation were synthesized and characterized. Structures are confirmed by IR, 1H and 13C NMR spectroscopy, and X-ray crystallography. The perchlorate salt was thermally stable, with a crystal density of 1.826 g cm−3 and its calculated energetic performance exceeded that of TNT. Except for the perchlorate, these salts are mechanically insensitive. This work explored the methyl sydnone imine cation as a suitable energetic compound, which was quickly obtained through facile syntheses. This is the first exploration of sydnone imines as components of energetic materials. [ABSTRACT FROM AUTHOR]

A series of new Cr(III) complexes of general formula [Cr{N,S}(THF)Cl3] (2a, N,S = PhS-2-PhCH = N-tBu; 2b, N,S = PhS-2-PhCH = N-C6H4-4-OMe; 2c, N,S = PhS-2-PhCH = N-C6H5; 2d, N,S = tBuS-2-PhCH = N-C6H5) were prepared and characterized by elemental analysis, IR spectroscopy and ESI-HRMS. DFT calculations confirm that the mer isomers are more stable by 23.9–34.3 kcal mol−1 than the fac isomers. Upon activation with methylaluminoxane (MAO), chromium precatalysts 2a–2d showed moderate activity in ethylene oligomerization (TOF = 3.4–26.6 × 103 (mol ethylene)(mol Cr)−1 h−1 at 80 °C) with a Schultz–Flory distribution of oligomers (KC4–C12 ≈ 0.90) and production of polymer varying from 1.2 to 9.8 wt%. The catalytic activity is mainly controlled by electronic effects at the thioether/imine groups. In general, the precatalysts bearing electron-donating substituents (tert-butyl, p-C6H4OMe) (2a, 2b and 2d) showed higher activities in comparison to 2c containing an electron-withdrawing (i.e., phenyl) substituent. Notably, the MAO loading has a strong influence on the activity of 2a. Thus, the use of 2000 equiv. led to a remarkable increase in the catalytic activity [TOF = 971 100 (mol ethylene) (mol Cr)−1 h−1] with high selectivity to formation of oligomers (98.8 wt%). [ABSTRACT FROM AUTHOR]

Commercial LiAlH4 can be used in catalytic quantities in the hydrogenation of imines to amines with H2. Combined experimental and theoretical investigations give deeper insight in the mechanism and identifies the most likely catalytic cycle. Activity is lost when Li in LiAlH4 is exchanged for Na or K. Exchanging Al for B or Ga also led to dramatically reduced activities. This indicates a heterobimetallic mechanism in which cooperation between Li and Al is crucial. Potential intermediates on the catalytic pathway have been isolated from reactions of MAlH4 (M=Li, Na, K) and different imines. Depending on the imine, double, triple or quadruple imine insertion has been observed. Prolonged reaction of LiAlH4 with PhC(H)=NtBu led to a side‐reaction and gave the double insertion product LiAlH2[N]2 ([N]=N(tBu)CH2Ph) which at higher temperature reacts further by ortho‐metallation of the Ph ring. A DFT study led to a number of conclusions. The most likely catalyst for hydrogenation of PhC(H)=NtBu with LiAlH4 is LiAlH2[N]2. Insertion of a third imine via a heterobimetallic transition state has a barrier of +23.2 kcal mol−1 (ΔH). The rate‐determining step is hydrogenolysis of LiAlH[N]3 with H2 with a barrier of +29.2 kcal mol−1. In agreement with experiment, replacing Li for Na (or K) and Al for B (or Ga) led to higher calculated barriers. Also, the AlH4− anion showed very high barriers. Calculations support the experimentally observed effects of the imine substituents at C and N: the lowest barriers are calculated for imines with aryl‐substituents at C and alkyl‐substituents at N. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: (E)‐α,β‐Unsaturated pyrazoleamides undergo facile dienolization to furnish copper(I)‐(1Z,3Z)‐dienolates as the major in the presence of a copper(I)‐(R)‐DTBM‐SEGPHOS catalyst and Et3N, which react with aldimines to afford syn‐vinylogous products as the major diastereoisomers in high regio‐ and enantioselectivities. In some cases, the diastereoselectivity is low, possibly due to the low ratio of copper(I)‐(1Z,3Z)‐dienolates to copper(I)‐(1Z,3E)‐dienolates. (Z)‐Allylcopper(I) species is proposed as effective intermediates, which may form an equilibrium with copper(I)‐(1Z,3Z)‐dienolates. Interestingly, the present methodology is a nice complement to our previous report, in which (E)‐β,γ‐unsaturated pyrazoleamides were employed as the prenucleophiles in the copper(I)‐catalyzed asymmetric vinylogous Mannich‐Type reaction and anti‐vinylogous products were obtained. In the previous reaction, copper(I)‐ (1Z,3E)‐dienolates were generated through α‐deprotonation, which might form an equilibrium with (E)‐allylcopper(I) species. Therefore, it is realized in the presence of a copper(I) catalyst that (E)‐α,β‐unsaturated pyrazoleamides lead to syn‐products and (E)‐β,γ‐unsaturated pyrazoleamides lead to anti‐products. Finally, by use of (E)‐β,γ‐unsaturated pyrazoleamide, (E)‐α,β‐unsaturated pyrazoleamide, (R)‐DTBM‐SEGPHOS, and (S)‐DTBM‐SEGPHOS, the stereodivergent synthesis of all four stereoisomers is successfully carried out. Then by following a three‐step reaction sequence, all four stereoisomers of N‐Boc‐2‐Ph‐3‐Me‐piperidine are synthesized in good yields, which potentially serve as common structure units in pharmaceutically active compounds. [ABSTRACT FROM AUTHOR]

New isomeric sensitizers containing an imine–carbene (IC)-based ancillary ligand, isomers IC101 and IC102, were designed for application in dye-sensitized solar cells (DSSCs). These ruthenium complexes were synthesized and isolated using simple purification methods. The DSSCs sensitized with IC101 and IC102 exhibited overall conversion efficiencies of 6.32% and 6.59%, respectively. Although these two isomers gave similar device output, reduction in the power conversion efficiency (5.52%) was observed when the cell was fabricated using a 1 : 1 mixture of both sensitizers. The results highlight the importance of isomeric purity of the sensitizing complexes to gain high performance DSSCs. [ABSTRACT FROM AUTHOR]

Pseudo-octahedral iron complexes supported by tridentate N^N^N-binding, redox 'non-innocent' diiminepyridine (DIP) ligands exhibit multiple reversible ligand-based reductions that suggest the potential application of these complexes as anolytes in redox flow batteries (RFBs). When bearing aryl groups at the imine nitrogens, substitution at the 4-position can be used to tune these redox potentials and impact other properties relevant to RFB applications, such as solubility and stability over extended cycling. DIP ligands bearing electron-withdrawing groups (EWGs) in this position, however, can be challenging to isolate via typical condensation routes involving para-substituted anilines and 2,6-diacetylpyridine. In this work, we demonstrate a high-yielding Zn-templated synthesis of DIP ligands bearing strong EWGs. The synthesis and electrochemical characterization of iron(II) complexes of these ligands is also described, along with properties relevant to their potential application as RFB anolytes. [ABSTRACT FROM AUTHOR]

N,O-Bis(tert-butoxycarbonyl)hydroxylamines are readily accessible as imine surrogates, which are bench stable and could quantitatively generate the corresponding imines for in situ applications. An unpresented catalytic asymmetric method for the synthesis of α-amino esters and ketones from novel imine surrogates, N,O-bis(tert-butoxycarbonyl)hydroxylamines, as well as its preliminary mechanistic studies are reported. A variety of optically enriched products were obtained in excellent yields and enantioselectivities (up to 99% yield and >99% ee). [ABSTRACT FROM AUTHOR]

Imine synthesis has enjoyed a long history as the dynamic covalent reaction of choice for the construction of purely covalent molecular architectures. In organic solvents, the formation of imine bonds is reversible but leads to thermodynamically stable products. In the presence of water, however, imine bonds are labile, a fact which limits their utility as mediators of self‐assembly in aqueous and biological media. In this Review, we discuss water‐compatible dynamic covalent bonds based on N‐substituted imine derivatives, namely hydrazones and oximes, for the self‐assembly of metal‐free organic architectures with well‐defined structures. The reasons why hydrazones and oximes are more robust in water than their parent imines are explained. Recent progress in the self‐assembly, characterization, and design principles of a variety of complex molecules including macrocycles, cages, catenanes, and knots in aqueous media is highlighted. Emerging applications for these molecules, including guest recognition and separations, are also discussed. [ABSTRACT FROM AUTHOR]