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Microorganisms participating in the development of biofilms exhibit heightened resistance to antibiotic treatment, therefore infections involving biofilms have become a problem in recent years as they are more difficult to treat. Consequently, research efforts are directed towards identifying novel molecules that not only possess antimicrobial properties but also demonstrate efficacy against biofilms. While numerous investigations have focused on antimicrobial capabilities of Schiff bases, their potential as antibiofilm agents remains largely unexplored. Thus, the objective of this article is to present a comprehensive overview of the existing scientific literature pertaining to small molecules categorized as Schiff bases with antibiofilm properties. The survey involved querying four databases (Web of Science, ScienceDirect, Scopus and Reaxys). Relevant articles published in the last 10 years were selected and categorized based on the molecular structure into two groups: classical Schiff bases and oximes and hydrazones. Despite the majority of studies indicating a moderate antibiofilm potential of Schiff bases, certain compounds exhibited a noteworthy effect, underscoring the significance of considering this type of molecular modeling when seeking to develop new molecules with antibiofilm effects. [ABSTRACT FROM AUTHOR]

Despite the astonishing diversity of naturally occurring biocatalytic processes, enzymes do not catalyze many of the transformations favored by synthetic chemists. Either nature does not care about the specific products, or if she does, she has adopted a different synthetic strategy. In many cases, the appropriate reagents used by synthetic chemists are not readily accessible to biological systems. Here, we discuss our efforts to expand the catalytic repertoire of enzymes to encompass powerful reactions previously known only in small-molecule catalysis: formation and transfer of reactive carbene and nitrene intermediates leading to a broad range of products, including products with bonds not known in biology. In light of the structural similarity of iron carbene (Fe═C(R1)(R2)) and iron nitrene (Fe═NR) to the iron oxo (Fe═O) intermediate involved in cytochrome P450-catalyzed oxidation, we have used synthetic carbene and nitrene precursors that biological systems have not encountered and repurposed P450s to catalyze reactions that are not known in the natural world. The resulting protein catalysts are fully genetically encoded and function in intact microbial cells or cell-free lysates, where their performance can be improved and optimized by directed evolution. By leveraging the catalytic promiscuity of P450 enzymes, we evolved a range of carbene and nitrene transferases exhibiting excellent activity toward these new-to-nature reactions. Since our initial report in 2012, a number of other heme proteins including myoglobins, protoglobins, and cytochromes c have also been found and engineered to promote unnatural carbene and nitrene transfer. Due to the altered active-site environments, these heme proteins often displayed complementary activities and selectivities to P450s.Using wild-type and engineered heme proteins, we and others have described a range of selective carbene transfer reactions, including cyclopropanation, cyclopropenation, Si-H insertion, B-H insertion, and C-H insertion. Similarly, a variety of asymmetric nitrene transfer processes including aziridination, sulfide imidation, C-H amidation, and, most recently, C-H amination have been demonstrated. The scopes of these biocatalytic carbene and nitrene transfer reactions are often complementary to the state-of-the-art processes based on small-molecule transition-metal catalysts, making engineered biocatalysts a valuable addition to the synthetic chemist's toolbox. Moreover, enabled by the exquisite regio- and stereocontrol imposed by the enzyme catalyst, this biocatalytic platform provides an exciting opportunity to address challenging problems in modern synthetic chemistry and selective catalysis, including ones that have eluded synthetic chemists for decades.

[40] Recently, pyrazolone-based MBH carbonates have emerged as versatile precursors to access spiropyrazolone scaffolds. Keywords: annulation; spiropyrazolones; diastereoselectivity; Morita-Baylis-Hillman carbonates; spirooxindoles EN annulation spiropyrazolones diastereoselectivity Morita-Baylis-Hillman carbonates spirooxindoles 1732 1738 7 08/18/23 20230901 NES 230901 Graph The construction of spiro carbocyclic/heterocyclic structures has received enormous attention from synthetic and medicinal-chemistry researchers in recent decades. Under the optimized reaction conditions, the pyrazolone MBH carbonates B 1a b - B c b reacted efficiently with the 3-methyleneoxindoles B 2a b - B v b to afford the corresponding spiropyrazolone oxindole derivatives B 3a b - B x b in good to excellent yields (up to 98%) and with very high diastereoselectivities (dr 99:1) (Scheme 1). [36] Despite these recent advances in synthesizing spiropyrazolone-fused oxindole derivatives, few methods have been described for the synthesis of a spirocyclic molecule bearing three different scaffolds, such as pyrazolone, oxindole, and cyclopentene, in a diastereoselective manner. [Extracted from the article]

A new class of spirocyclic imines (SCIs) has been theoretically investigated by applying a variety of quantum chemical methods and basis sets. The uniqueness of these compounds is depicted by various peculiarities, e.g., the incidence of planar six-membered rings each with two imine groups (two π bonds) and the incorporation of the isosteres carbon, silicon, or germanium spiro centers. Additional peculiarities of these novel SCIs are mirrored by their three-dimensionality, the simultaneous occurrence of nucleophilic and electrophilic centers, and the cross-hyperconjugative (spiro-conjugation) interactions, which provoke charge mobility along the spirocyclic scaffold. Substitution of SCIs with strong electron-withdrawing substituents, like the cyano group or fluorine, enhances their docking capability and impacts their reactivity and charge mobility. To gain thorough knowledge about the molecular properties of these SCIs, their structures have been optimized and various quantum chemical concepts and models were applied, e.g., full NBO analysis and the frontier molecular orbitals (FMOs) theory (HOMO-LUMO energy gap) and the chemical reactivity descriptors derived from them. For the assessment of the charge density distribution along the SCI framework, additional complementary quantum chemical methods were used, e.g., molecular electrostatic potential (MESP) and Bader's QTAIM. Additionally, using the aromaticity index NICS (nuclear independent chemical shift) and other criteria, it could be shown that the investigated cross-hyperconjugated sila and germa SCIs are spiro-aromatics of the Heilbronner Craig-type Möbius aromaticity. [ABSTRACT FROM AUTHOR]

In this work, the synthesis and structure of an antimony complex with an aromatic, asymmetric tridentate ligand without an Sb-C bond were studied. Ethoxy(2-salicylidenaminophenolato)antimony(III) was studied with NMR, UV-Vis, and IR spectroscopy and the molecular structure was determined by single crystal X-ray diffraction. The antimony atom is formally tetracoordinate in this molecule. Coordinative unsaturation becomes visible in the solid-state structure where intermolecular Sb...O interactions supplement the coordination sphere of the antimony atom to be hexacoordinated. Quantum chemical calculations were performed in order to obtain a better understanding of the bond properties in the antimony complex. These show a spherical distribution of the lone pair at antimony and polar shared bonds from antimony to the heteroatoms of the tridentate ligand. [ABSTRACT FROM AUTHOR]

The reaction of [Ru(PPh3)3Cl2] with a group of four 1,4-diazabutadiene ligands (p-RC6H4N＝C(H)–C(H)＝NC6H4R-p; R = OCH3, CH3, H and Cl; abbreviated as L-R) in an equimolar ratio afforded chloro-bridged di-ruthenium complexes (1–4) of the general type [Ru2(PPh3)2(L-R)2Cl3]Cl. The crystal structures of complexes 1 (R = OCH3), 2 (R = CH3) and 4 (R = Cl) were determined and the molecular structure of complex 3 (R = H) was optimized using the DFT method. Each complex showed four intense absorptions in the visible and ultraviolet regions, the origin of which was probed employing TDDFT calculations. The complexes were found to serve as efficient catalyst precursors for the oxidative and deaminative C–N coupling of a series of primary amines, producing corresponding imines in good yields. Homo-coupling of benzylamines and cross-coupling of two differently substituted benzylamines or benzylamine with anilines and other aryl/alkyl amines could be realized using this catalytic protocol with aerial oxygen as the oxidant. [ABSTRACT FROM AUTHOR]

Herein, we demonstrate the first example of a multistep solid-state organic synthesis, in which a new imine-linked two-dimensional covalent organic framework (COF-170, 1) was transformed through three consecutive postsynthetic modifications into porous, crystalline cyclic carbamate and thiocarbamate-linked frameworks. These linkages are previously unreported and inaccessible through de novo synthesis. While not altering the overall connectivity of the framework, these chemical transformations induce significant conformational and structural changes at each step, highlighting the key importance of noncovalent interactions and conformational flexibility to COF crystallinity and porosity. These transformations were assessed using 15N multiCP-MAS NMR spectroscopy, providing the first quantitation of yields in COF postsynthetic modification reactions, as well as of amine defect sites in imine-linked COFs. This multistep COF linkage postsynthetic modification represents a significant step toward bringing the precision of organic solution-phase synthesis to extended solid-state compounds.

A robust synthetic route from L-hydroxyproline (L-Hyp) to phosphines has established an expandable library of six chiral aminophosphines, which were then applied to the phosphine-catalyzed [4 + 2] allene-imine annulation. The enantioinduction in the annulations-induced by a purely steric effect-were moderate (up to 57% ee). A switch of the reaction site from the γ- to the β'-carbon atom of the allenoate was observed during the annulations performed using sterically demanding chiral phosphines.

Since the first reports of the reaction of imines and cyclic anhydrides by Castagnoli and Cushman, this procedure has been applied to the synthesis of a variety of lactams, some of them with important synthetic or biological interest. The scope of the reaction has been extended to the use of various Schiff bases and anhydrides as well as to different types of precursors for these reagents. In recent years, important advances have been made in understanding the mechanism of the reaction, which has historically been quite controversial. This has helped to develop reaction conditions that lead to pure diastereomers and even homochiral products. In addition, these mechanistic studies have also led to the development of new multicomponent versions of the Castagnoli–Cushman reaction that allow products with more diverse and complex molecular structures to be easily obtained. [ABSTRACT FROM AUTHOR]

Reaction options, alkoxide vs hydroxide vs amine addition to the key intermediate (o-nitrosoimine) generated in the Davis-Beirut reaction of an o-nitrobenzylamine substrate, are reported to explain the nucleophilic addition selectivity of this one-pot indazole-forming process. The hydroxide addition/deprotection pathway as well as the fate of the resulting o-nitrosobenzaldehyde were both uncovered with several o-nitrobenzylamine substrates, and design elements required for an efficient double Davis-Beirut reaction, inspired by new mechanistic insights, were defined.

The geometries, stabilities, and 1,3-dipolar cycloaddition reactivities of 24 mesoionic azomethine ylides and imines were investigated using density functional theory calculations at the M06-2X/6-311+G-(d,p)/M06-2X/6-31G-(d) level. The computed structures highlight how the commonly used "aromatic" resonance form should be replaced by two more accurate resonance structures. Stabilities of the dipoles were assessed by various homodesmotic schemes and are consistent with these compounds being nonaromatic. The activation free energies with ethylene or acetylene range from 11.8 to 36.6 kcal/mol. Within each dipole type, the predicted cycloaddition reactivities correlate with the reaction energies and the resonance stabilization energies provided by the various substituents. Endocyclic (X) heteroatoms increase the reactivity of the 1,3-dipoles in the order of O > NH ≅ S, whereas exocyclic (Y) substituents increase it in the order of CH2 > NH > O > S. Distortion/interaction analysis indicated that the difference in reactivity between differently substituted 1,3-dipoles is driven by distortion, whereas the difference between azomethine ylides and imines is related to lower interaction energies of imines with the dipolarophiles.

A novel organic small molecule, 5-(4-(diphenylamino)phenyl)-1-octylindoline-2,3-dione (TPI) containing an alkyl chain substituted electron accepting isatin (indoline-2,3-dione) and strong electron withdrawing N, N-diphenylaniline units have been synthesized through Suzuki coupling reaction. The molecular structure of TPI is confirmed by NMR, FT-IR, and Mass spectroscopy techniques. The TPI molecule exhibits a low band gap of approximately ∼ 2.03 eV which is also supported by the DFT results. The influence of additive and heat treatment on the electronic, morphological, and photovoltaic performance of organic solar cells was investigated meticulously. The TPI donor exhibits complementary light absorption with fullerene acceptor in combination with DIO and TA which efficiently absorb the photon in the 300–730 nm range. The TPI was later used as an electron donor material for the fabrication of organic solar cells. Remarkably, the morphology-dependent optimized TPI:PC 71 BM (1:3.0) exposed excellent power conversion efficiency (PCE) of about ∼ 5.56 % with enhanced V OC of ∼ 0.811 V, J SC of 11.81 mA cm−2 and FF of 55.3 % fabricated in addition with DIO and thermal annealing treatment. Most importantly, the unencapsulated devices maintained > 96 % of the initial PCE value after 240 h under ambient temperature. Our findings indicate that isatin-derived small molecules with simple architecture propose great potential for promising BHJ-OSCs material. [Display omitted] • A new D–A type small molecule donor TPI was prepared as efficient material for organic solar cells (OSCs). • The electron-rich isatin and electron-donating triphenylamine (TPA) unit in the TPI improved crystallinity and charge transport in the active layer. • The influence of DIO additive and thermal annealing treatment on the OSCs performance was investigated. • The fabricated devices express PCE of ∼ 5.56 % with improved photovoltaic parameters and room temperature stability. [ABSTRACT FROM AUTHOR]

A copper-catalyzed, chemoselective hydrometalation process enables the use of simple allenes as allylmetal nucleophile surrogates in imine allylation reactions. By modulating the nitrogen-protecting group, either highly branched- or linear-selective addition can be achieved from the same allene. Both reactions exhibit excellent diastereoselectivity and broad functional-group tolerance. Preliminary results indicate that good enantioselectivity can also be achieved in the linear-selective reaction. Finally, a mechanistic model for the regiodivergence is proposed on the basis of density functional theory calculations.

The copper-catalyzed intermolecular enantioselective addition of styrenes to imines has been achieved under mild conditions at ambient temperature. This process features the use of styrenes as latent carbanion equivalents via the intermediacy of catalytically generated benzylcopper derivatives, providing an effective means for accessing highly enantiomerically enriched amines bearing contiguous stereocenters. Mechanistic studies shed light on the origin of the preferential styrene hydrocupration in the presence of an imine with the Ph-BPE-derived copper catalyst.

Molecular and crystal structures of two octahedral zinc complexes with chelated N-phosphorylated thiobenzamide ligands and nitrogen bidentate aromatic ligands (bipyridyl and phenanthroline) are determined by XRD. It is shown that the zinc atom in the complexes with thiobenzamide ligands is coordinated (in contrast to the complex with an amino group at the carbon atom of the thiacarbamate ligand) by sulfur and oxygen atoms of thiocarbonyl and phosphoryl groups to form six-membered metallacycles. [ABSTRACT FROM AUTHOR]

In the quest for 3,3‐dichloro‐β‐lactam building blocks, the serendipitous formation of 2,2‐dichloro‐N‐(chloromethyl)acetamides was observed. This peculiar reactivity was investigated in detail, both experimentally and computationally by means of Density Functional Theory (DFT) calculations. 2,2‐Dichloro‐N‐(chloromethyl)acetamides were thus shown to be formed experimentally through reaction of 2,2‐dichloroacetyl chloride with glyceraldehyde‐derived imines, i. e. (2,2‐dimethyl‐1,3‐dioxolan‐4‐yl)methanimines, bearing aromatic N‐substituents, in the presence as well as in the absence of a base. Deployment of aliphatic imines, however, resulted in complex reaction mixtures, pointing to the importance of a stabilizing aromatic substituent at nitrogen. The DFT results indicate that the substituents can alter the governing equilibria on the one hand and intrinsic barrier heights for the different routes on the other hand, showing that these are controlling the reaction outcome. Furthermore, the 2,2‐dichloro‐N‐(chloromethyl)acetamides proved to be rather unstable in solution and thus difficult to isolate. Nonetheless, their molecular structure was confirmed by means of NMR analysis of several purified analogs and X‐ray study of a 4‐methoxyphenyl derivative. [ABSTRACT FROM AUTHOR]

A novel three-coordinated tin(II) chloride [Ph2P(NtBu)2]SnCl (1) supported by an N,N′-di-tert-butyliminophosphonamide having two phenyl groups on the phosphorus atom was synthesized by the reaction of the starting lithium iminophosphonamide [Ph2P(NtBu)2]Li with SnCl2·(dioxane) in toluene. The molecular structure of 1 was established by X-ray diffraction analysis. Tin(II) chloride 1 can act as an efficient precatalyst for the hydroboration of a wide variety of aldehydes, ketones, and imines at −10 °C. DFT calculations propose that hydroboration involves hydride transfer from the corresponding tin(II) hydride intermediate [Ph2P(NtBu)2]SnH (10) to the carbonyl substrates via four-membered transition states (TS-12), affording three-coordinated tin(II) alkoxide intermediates [Ph2P(NtBu)2]SnOR (13), followed by the stepwise reaction of 13 with HBpin (pin = pinacolate) to release the boronate esters and regenerate the tin(II) hydride 10. The stoichiometric reaction of the in site-generated 10 with benzophenone 2a at −10 °C led to the formation of 13. Moreover, 13 also stoichiometrically reacted with HBpin at −10 °C, forming the corresponding boronate ester 3a and 10 based on the 1H NMR spectrum of the reaction mixture. [ABSTRACT FROM AUTHOR]

The enantioselective silver-catalyzed propargylation of N-sulfonylketimines is described. This reaction proceeds in high yield and excellent enantiomeric ratio and is compatible with a wide variety of diaryl- and alkylketimines. Synthetic transformations of homopropargylic products via enyne ring-closing metathesis, Sonogashira cross-coupling, and reduction reactions proceed with high stereochemical fidelity. Both allenyl and propargyl borolane reagents can be used to obtain homopropargylic products, a distribution most consistent with a mechanism involving transmetalation of the silver catalyst with the borolane reagent.

Pinnatoxins are macrocyclic imine phycotoxins associated with algal blooms and shellfish toxicity. Functional analysis of pinnatoxin A and pinnatoxin G by binding and voltage-clamp electrophysiology on membrane-embedded neuronal α7, α4β2, α3β2, and muscle-type α12βγδ nicotinic acetylcholine receptors (nAChRs) reveals high-affinity binding and potent antagonism for the α7 and α12βγδ subtypes. The toxins also bind to the nAChR surrogate, acetylcholine-binding protein (AChBP), with low Kd values reflecting slow dissociation. Crystal structures of pinnatoxin-AChBP complexes (1.9-2.2 Å resolution) show the multiple anchoring points of the hydrophobic portion, the cyclic imine, and the substituted bis-spiroketal and cyclohexene ring systems of the pinnatoxins that dictate tight binding between the opposing loops C and F at the receptor subunit interface, as observed for the 13-desmethyl-spirolide C and gymnodimine A congeners. Uniquely, however, the bulky bridged EF-ketal ring specific to the pinnatoxins extends radially from the interfacial-binding pocket to interact with the sequence-variable loop F and govern nAChR subtype selectivity and central neurotoxicity.

The first asymmetric intermolecular addition of non-acidic C-H bonds to imines is reported. The use of the activating N-perfluorobutanesulfinyl imine substituent is essential for achieving sufficient reactivity and provides outstanding diastereoselectivity (>98:2 dr). Straightforward removal of the sulfinyl group with HCl yields the highly enantiomerically enriched amine hydrochlorides.

Sulfone-substituted γ- and δ-lactams have been prepared in a single step with high diastereoselectivity. Sulfonylglutaric anhydrides produce intermediates that readily decarboxylate to provide δ-lactams with high diastereoselectivity. Substituents at the 3- or 4-position of the glutaric anhydride induce high levels of stereocontrol. Sulfonylsuccinic anhydrides produce intermediate carboxylic acids that can be trapped as methyl esters or allowed to decarboxylate under mild conditions. This method has been applied to a short synthesis of the pyrrolizidine alkaloid (±)-isoretronecanol.

Computations (SCS-MP2//B3LYP) reveal that the asymmetric synthesis of highly substituted γ-lactams with three stereogenic centers, including one quaternary center, proceeds through a Mannich reaction between the enol form of the anhydride and the E-imine, followed by a transannular acylation. This new mechanistic picture accounts for both the observed reactivity and stereoselectivity. CH-O and hydrogen bonding interactions in the Mannich step and torsional steering effects in the acylation step are responsible for stereocontrol. It is demonstrated that this new mechanistic picture applies to the related reactions of homophthalic anhydrides with imines and presents new vistas for the design of a new reaction to access complex molecular architectures.

A reaction between imines and anhydrides has been developed with chiral disubstituted anhydrides and chiral imines. The synthesis of highly substituted γ-lactams with three stereogenic centers, including one quaternary center, proceeds at room temperature in high yield and with high diastereoselectivity in most cases. Enantiomerically pure alkyl-substituted anhydrides proceed with no epimerization, thus providing access to enantiomerically pure penta-substituted lactam products.

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]

Herein, we report the synthesis of a series of push–pull imines by considering cyclic diamino substituent at the C‐centre and fluoroaryl substituent at the N‐centre. This has been achieved by a selective aromatic nucleophilic substitution of different fluoroarenes by N‐H‐substituted N‐heterocyclic imines (NHIs) at ambient conditions without any additional reagent. Solid‐state molecular structure analysis reveals the elongation of the central C–N bond of the imine functionality, which is consistent with the push–pull nature of these imines. The push–pull nature of these imines is further validated by computational studies. [ABSTRACT FROM AUTHOR]

The condensation reactions of 5-bromoacenaphthenequinone with 2,6-diisopropylaniline and 4‑bromo-2,6-di-iso-propylaniline afford new mono- and tribromosubstituted bis(arylimino)acenaphthenes: 1,2-bis[(2,6-diisopropylphenyl)imino]-5-bromacenaphthene (Dpp-Br-Bian) (L1) and 1,2-bis[(4-bromo-2,6-diisopropylphenyl)imino]-5-bromacenaphthene (p-Br-Dpp-Br-Bian) (L2), respectively. Compounds L1 and L2 act as neutral ligands in the [(Dpp-Br-Bian)ZnCl2] (I), [(p-Br-Dpp-Br-Bian)AlCl3] (III), and [(p-Br-Dpp-Br-Bian)GaCl3] (IV) complexes synthesized by the reactions of free diimines with the corresponding metal chlorides. The reaction of the known dibromosubstituted derivative 1,2-bis[(4-bromo-2,6-di-iso-propylphenyl)iminoacenaphthene (p-Br-Dpp-Bian) (L3) with copper(I) chloride also affords complex [(p-Br-Dpp-Bian)CuCl] (II) with the neutral diimine ligand. New compounds L1, L2, and I–IV are characterized by NMR, IR spectroscopy, and elemental analysis. The molecular structure of complex I is determined by X-ray structure analysis. [ABSTRACT FROM AUTHOR]

Three copper(I) complexes, [CuCl(L)(PPh3)2] [L = FL (1), BL (2) or TL (3)] were prepared from [(PPh3)2Cu(µ‐Cl)2Cu(PPh3)] and N‐carbamothioylfuran‐2‐carboxamide (FL), N‐carbamothioylbenzamide (BL) or N‐carbamothioylthiophene‐2‐carboxamide (TL) ligands in benzene and four‐coordinated tetrahedral copper complexes were well characterized by various spectroscopic techniques (UV/Vis, FT‐IR, 1H NMR, 13C NMR and 31P NMR). The molecular structure of the ligands (FL and BL) and complexes was established from single‐crystal X‐ray diffraction studies. Copper complexes have been shown to catalyse the one‐pot synthesis of imines and quinoxalines. Heterogenized catalyst (4) was prepared by reacting more active complex 3 with polystyrene supported triphenylphosphane, and characterized by elemental analyses, and DRS‐UV, FT‐IR, ICP‐OES, and solid‐state NMR techniques. Catalytic activity of the complexes (3 and 4) was tested in the formation of imines from alcohols and amines, and quinoxalines from hydroxy ketones and diamines. Heterogeneity and reusability of catalyst 4 were evaluated, and the catalyst can be reused for four runs without any loss in activity. [ABSTRACT FROM AUTHOR]

The reaction of the hydride [(dpp-bian)Al(H)Cl] (1) containing the 1,2-bis[(2,6-diisopropylphenyl) imino]acenaphthene (dpp-bian) radical anion with MeLi affords the compound [(dpp-bian)Al(H)Me] (2). The reaction of complex 1 with two equivalents of PhC≡CNa involves the replacement of chlorine along with oxidative substitution of hydrogen accompanied by the reduction of dpp-bian to the dianion to form the compound [(dpp-bian)Al(C≡CPh)2Na(Et2O)2] ({sn3}). This reaction gives the complex [{dpp-bian(H)}Al(C≡CPh)3Na(Et2O)2] (4) as the second product, which is apparently generated in the reaction of compound 3 with PhC≡CH. The reaction of compound 1 with Cp*Na (Cp* is pentamethylcyclopentadiene) in dimethoxyethane is also accompanied by the reduction of redox-active dpp-bian to the dianion, giving the complex [(dpp-bian)Al(H)Cl][Na(DME)3] (5). Diamagnetic derivatives 3-5 were characterized by 1H NMR spectroscopy; paramagnetic compound 2, by EPR spectroscopy. The molecular structures of compounds 2-5 were determined by X-ray diffraction. [ABSTRACT FROM AUTHOR]

The oxidation of [(Dpp-Bian)Eu(Dme)2] (I) (Dpp-Bian is the 1,2-bis[(2,6-diisopropylphenyl) imino]acenaphthene dianion, Dme = 1,2-dimethoxyethane), prepared in situ, with 0.5 mol equiv. of iodine in Thf gives europium(II) dimer, [(Dpp-Bian)Eu(μ-I)(Thf)2]2 (II) (Thf = tetrahydrofuran), with the Dpp-Bian ligand as radical anion. The exchange reaction of II with potassium dithiocarbamate affords europium( II) dimer, [(Dpp-Bian)Eu[SC(S)NMe2](Thf)]2 (III), which also contains the Dpp-Bian radical anion. However, the oxidation of the ytterbium complex [(Dpp-Bian)Yb(Dme)2] (IV) with 0.5 mol equiv. of [Me2NC(S)S]2 gives the monomeric product [(Dpp-Bian)Yb[SC(S)NMe2](Dme)] (V), in which Dpp-Bian is still the dianion and the ytterbium atom is oxidized to the trivalent state. The reaction of II with potassium thiocyanate gives europium(II) isothiocyanate complex with the radical anion diimine ligand [(Dpp-Bian)Eu(NCS)(Dme)2] (VI). The molecular structures of complexes II, III, V, and VI were determined by X-ray diffraction (CIF files CCDC 1576687-1576690, respectively). [ABSTRACT FROM AUTHOR]

Scaffold hopping, the exchange of a specific portion of a potential active ingredient with another substructure with the aim of finding isofunctional molecular structures with significantly different molecular backbones, often offers the chance in lead discovery or optimization to mitigate problems related to toxicity, intellectual property, and insufficient potency or stability. Scaffold hopping tools such as isosteric ring replacement including 1,3 nitrogen shift and cyclic imine-amide isosterism, but also ring opening and ring closure approaches, functional group isosterism, reversion of functional groups, chain shortening, chain lengthening, and scaffolds delivered by natural products, have become a permanent fixture of the innovation and optimization process in crop protection research. Their appropriate use will be explained through examples of success stories in the field of agrochemistry. Analogies to, but also differences from, the main categories of scaffold hopping in medicinal drug discovery are discussed. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]