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This account is a collection of vignettes describing new reactions discovered in the author's group revolving around the chemistry of oximes. They range from ionic transformations, including reduction to unsubstituted imines and the formation of α-electrophiles, to the generation and capture of iminyl radicals, to a general synthesis of alkynes. The mechanistic reasonings and occasional serendipitous observations underlying these discoveries are discussed briefly. [ABSTRACT FROM AUTHOR]

A new strategy to access α‐functionalized alicyclic amines via their corresponding imine‐BF3 complexes is reported. Isolable imine‐BF3 complexes, readily prepared via dehydrohalogenation of N‐bromoamines in a base‐promoted/18‐crown‐6 catalyzed process followed by addition of boron trifluoride etherate, undergo reactions with a wide range of organometallic nucleophiles to afford α‐functionalized azacycles. Organozinc and organomagnesium nucleophiles add at ambient temperatures, obviating the need for cryogenic conditions. In situ preparation of imine‐BF3 complexes provides access to α‐functionalized morpholines and piperazines directly from their parent amines in a single operation. α‐Functionalized morpholines can be elaborated further, for instance by installing a second substituent in the α′‐position. [ABSTRACT FROM AUTHOR]

A thiourea organocatalyst efficiently promoted the asymmetric cascade Michael/Michael reactions between isatin‐derived trifluoromethylacrylate and α‐alkylidene succinimide, resulting in high yields of spirooxindole derivatives. These compounds exhibit vicinal all‐carbon quaternary stereocenters and bear a trifluoromethyl group, with excellent enantioselectivities reaching up to 99 % ee. This work represents the first successful organocatalyst application for the direct construction of vicinal all‐carbon quaternary stereocenters, featuring a trifluoromethyl group. [ABSTRACT FROM AUTHOR]

Spirolides (SPXs), gymnodimines (GYMs), and pinnatoxins (PnTXs) have been detected in shellfish from the northwestern Mediterranean coast of Spain. Several samples of bivalves were collected from Fangar Bay and Alfacs Bay in Catalonia over a period of over 7 years (from 2015 to 2021). Shellfish samples were analyzed for cyclic imines (CIs) on an LC1200 Agilent and 3200 QTrap triple–quadrupole mass spectrometer. In shellfish, SPX-1 was detected in two cases (of 26.5 µg/kg and 34 µg/kg), and GYM-A was only detected in trace levels in thirteen samples. Pinnatoxin G (PnTX-G) was detected in 44.6% of the samples, with its concentrations ranging from 2 µg/kg to 38.4 µg/kg. Statistical analyses revealed that seawater temperature influenced the presence or absence of these toxins. PnTX-G showed an extremely significant presence/temperature relationship in both bays in comparison to SPX-1 and GYM-A. The prevalence of these toxins in different bivalve mollusks was evaluated. A seasonal pattern was observed, in which the maximum concentrations were found in the winter months for SPX-1 and GYM-A but in the summer months for PnTX-G. The obtained results indicate that it is unlikely that CIs in the studied area pose a potential health risk through the consumption of a seafood diet. However, further toxicological information about CIs is necessary in order to perform a conclusive risk assessment. [ABSTRACT FROM AUTHOR]

Approximately 1,3-Dipolar cycloaddition of imidazolidine derivatives containing exocyclic double bonds is a convenient method of creating spiro-conjugated molecules with promising anticancer activity. In this work, the derivatives of parabanic acid (2-thioxoimidazolidine-4,5-diones and 5-aryliminoimidazolidine-2,4-diones) were first investigated as dipolarophiles in the reactions with nitrile imines. The generation of nitrile imines was carried out either by the addition of tertiary amine to hydrazonoyl chlorides «drop by drop» or using the recently proposed diffusion mixing technique, which led to ~5–15% increases in target compound yields. It was found that the addition of nitrile imines to C=S or C=N exocyclic double bonds led to 1,2,4-thiazolines or triazolines and occurred regioselectively in accordance with the ratio of FMO coefficients of reactants. The yield of the resulting spiro-compound depended on the presence of alkyl substituents in the nitrile imine structure and was significantly decreased in reactions with imines with strong electron donor or electron-withdrawing groups. Some of the obtained compounds showed reasonable in vitro cytotoxicity. IC50 values were calculated for HCT116 (colon cancer) cells using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) test. [ABSTRACT FROM AUTHOR]

A novel Co(OAc)2/N-hydroxyphthalimide (NHPI)-catalyzed oxidation of 3-arylmethyl sulfonyl imines to prepare 3-arylcarbonyl analogues has been realized. 3-Arylcarbonyl sulfonyl imines were comprehensively synthesized from benzyl substrates for the first time. The reactions proceeded in moderate to excellent yields. Mechanistic investigation suggests that 3-(hydroperoxy(phenyl)methyl)benzo[d]isothiazole 1,1-dioxide A is the key intermediate for the formation of products 2. [ABSTRACT FROM AUTHOR]

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]

A three‐component 1,4‐addition variant of the Ugi reaction involving carboxylic acids, isocyanides, and cyclic α,β‐unsaturated imines is presented in this study. The cyclic α,β‐unsaturated imines were conveniently prepared through the oxidative dearomatization of N‐substituted anilines. The reaction proceeded successfully to produce a sole diastereomer, and the relative configuration was determined through 2D NMR and X‐ray diffraction analysis. [ABSTRACT FROM AUTHOR]

A series of syringaldehyde imines with para-substituted anilines have been synthesized in a good yield, and their crystal structures have been analyzed. The orientation of the syringaldehyde hydroxyl group plays in important role in the intermolecular hydrogen-bonding pattern of the molecules. The O–H...N hydrogen bonding interactions primarily determine the three-dimensional packing of the molecules, even though they make up a relatively small percentage of intermolecular interactions in the molecules. The three structures with the p-hydroxy group cis to the imine group give hydrogen-bonded zigzag chains in the monoclinic crystals, while the structure with a trans hydroxy group crystallize in a hexagonal space group ( R 3 ¯ ) and form hydrogen-bonded hexamers. The hexagonal structure also displays Br...Br interactions, forming additional hexameric clusters. The analysis of published p-hydroxyphenyl imine crystal structures from the Cambridge Crystallographic Database revealed patterns in the length of the hydrogen bonding interactions based on steric congestion around the hydroxyl group. [ABSTRACT FROM AUTHOR]

An efficient approach for the reduction of cyclic N‐sulfonylimines using N‐heterocyclic carbene boranes as the hydride donor was developed, leading to various cyclic sulfamates and sulfonamides in excellent yields. The approach had broad scope including both the N‐sulfonyl aldimines and ketimines under mild reaction conditions, which proves that the NHC‐boranes are good alternatives as the reductive reagents. [ABSTRACT FROM AUTHOR]

Three‐component tandem Ritter and Mannich reactions were developed for one‐pot arylation and acyl protected amination of isatin. The acid catalyzed reaction produced wide variety of 3‐aryl‐3‐amidooxindoles directly from commercially available isatin. The C3 functionalization of isatin is affected by condensation with electron rich arenes and nitriles or amides with concomitant C−C and C−N bonds formation. Substituted isatins, different nucleophiles (cyclic and acyclic N, N‐disubstituted arylamines), aliphatic nitriles, and amides expanded the scope of the reaction. The reaction is simple, general, efficient and can switch the amidation substrate from nitriles in Ritter reaction to amides in Mannich reaction. [ABSTRACT FROM AUTHOR]

A new phosphine‐catalyzed reaction of α‐substituted allenes with aryl imines, in stark contrast to classic cycloaddition reactions, has been developed. This reaction delivers valuable highly functionalized itaconimides with excellent stereoselectivities by a new «un‐cyclizing» reaction mode involving β′‐carbon of α‐substituted allenes. Moreover, the present «un‐cyclizing» reaction can also be carried out in a one‐pot fashion and scaled up to the gram scale by using aryl aldehydes, without the need to isolate the aryl imines. Mechanistic studies and control experiments reveal the crucial role of H2CO3 for the present reaction mode. In addition, density functional theory (DFT) calculations were performed to understand the possible mechanism. [ABSTRACT FROM AUTHOR]

In a climate change context, N2O contributes to global warming with CO2 and CH4. As an inert molecule, its upgrading as oxidant still constitutes a challenge in chemical synthesis. Here, the synthesis of imines was unprecedently performed using nitrous oxide (N2O) as a novel and highly selective oxidative agent for the photocatalytic homo‐coupling of amines. In a similar way, unsymmetric imines were produced through cross‐coupling of amines with alcohols. Promisingly, this greenhouse gas showed excellent performances towards the target reactions when photocatalytically activated at atmospheric pressure, with silver photodeposited on titanium dioxide as catalyst. Relevantly, reactions under N2O atmosphere exhibited high conversion rates and turn‐over frequencies, and higher selectivities than the ones carried out under a dioxygen atmosphere. Mechanisms for both reactions were detailed, showing the release of nitrogen and water as benign by‐products. [ABSTRACT FROM AUTHOR]

An asymmetric three‐component reaction of α‐H diazoacetate with sulfonamide and imine has been developed under the co‐catalyzation of Rh2(OAc)4 and a chiral phosphoric acid (CPA), which proceed through Mannich‐type interception of transient ammonium ylide. The reaction offers a convenient access to α, β‐diamine acid derivatives with two adjacent chiral centers in 59%‐74% yields with 91%‐99% ee and 92:8 to>95:5 dr. Moreover, the generated products could be easily converted to free chiral diamines and other useful chiral motifs. [ABSTRACT FROM AUTHOR]

Rhodium-catalyzed three-component C–H bond activation of aromatics with amides and aldehydes to synthesize amines was established. The addition of copper was found to be essential to ensure the high reactivity. The mechanistic studies indicated that key intermediates formed by the transmetallization between rhodium and copper could further promote the addition between 2-(pyridin-2-yl)-phenyl-metal species and imines. A series of densely substituted amines could be conveniently prepared by this one-step, three-component procedure from commercially available substrates via C–H bond activation with water as the only by-product. [ABSTRACT FROM AUTHOR]

Under phosphine catalysis facilitated through desilylation, intramolecular annulation/nucleophilic addition of trimethylsilylethynyl benzoxazinanones with electron‐deficient imines or alkenes was achieved to afford a series of indole derivatives in moderate to high yields. The trimethylsilylethynyl benzoxazinanones without electron‐withdrawing group on the alkyne moiety functioned as phosphine acceptors. Notably, the distinctive desilylation activation played a key role in catalytic process. Particularly, those indole derivatives could be readily transformed into various biologically significant γ‐carboline compounds. The use of chiral phosphine achieved asymmetric reaction, leading to a 95% ee of product. [ABSTRACT FROM AUTHOR]

A visible‐light induced multicomponent reaction of aromatic aldehydes, amines and sodium difluoromethanesulfinate for the synthesis of fluorinated secondary amines has been investigated. The protocol affords a convenient pathway for the introduction of difluoromethyl group into imines, which generated in situ by the reaction of aldehydes and amines. A diverse range of fluorinated secondary amines were synthesized in 43%–79% yields under room temperature. In addition, a plausible mechanism was proposed based on several control experiments. [ABSTRACT FROM AUTHOR]

A phosphine‐catalyzed (3+2) annulation of Morita‐Baylis‐Hillman carbonates with pyrazolinone‐derived ketimines has been achieved to give various spirodihydropyrrole‐dihydropyrazolones in moderate to high yields with good diastereoselectivities. The reaction tolerated diverse MBH carbonates and ketimines. Both scale‐up reaction and further transformation of the product were successfully performed. In addition, up to 98 % ee of chiral product was obtained with the use of chiral bifunctional phosphine. [ABSTRACT FROM AUTHOR]

The reactions of oxialyl chloride with pyrene, 2,7-di-tert-butylpyrene, anthracene and 4,7-di-tert-butyl-1,2-dihydroacenaphthylene give the corresponding diketones: cyclopent[cd]pyrene-3,4-dione, 2,7-di-tert-butylcyclopenta[cd]pyrene-3,4-dione, aceanthrylene-1,2-dione, 1,2-diketo-3,8-di-tert-butylpyracene. The diketones react with 2,6-diisopropylaniline to form a series of the corresponding imines. It was shown that 1,2-diketo-3,8-di-tert-butylpyracene does not produce condensation products with 2,6-diisopropylaniline. The effect of the imine substituents on the electronic structure and UV spectra of the aceanthrylene derivatives was studied with by DFT and TD DFT. Structure of 1,2-diketo-3,8-di-tert-butylpyracene, as well as (E)-2-(2,6-diisopropylphenylimino)aceanthrylen-1(2H)-one and 3,4-bis[2,6-diisopropylphenylimino]aceanthrylene was characterized by single crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

The addition of carbon electrophiles to carbonyls and imines has emerged as a valuable strategy for the construction of C−C bonds. The merger of this concept with sustainable cobalt catalysis has yielded numerous innovative methodologies. Remarkable functional group tolerance and selectivity have been observed in many cases, providing reliable methods for bond construction. The cobalt‐catalyzed additions of carbon electrophiles to carbonyls, imines and carboxylic acid derivatives described in this review include the earliest reports, such as Takai‐Utimoto Co/Cr co‐catalyzed additions and their progression, as well as modern variants, exemplified by recent Co/photoredox co‐catalyzed protocols. The systematic appraisal of this modern strategy provides a clearer perspective and inspiration for its further development. [ABSTRACT FROM AUTHOR]

New tin(IV) complexes based on various pyrocatechols containing tert-butyl and tert-octyl substituents in the aromatic ring are synthesized and structurally characterized. Reduction of spatially hindered o-quinones with tin amalgam in tetrahydrofuran allows the preparation of compounds with the trans-position of catecholate ligands in the metal coordination sphere. In the further reaction of synthesized tin(IV) biscatecholates with N-donor ligands (pyridine (Py), α,α′-dipyridyl (dipy), 1,10-phenanthroline (phen), pyrazino-[2,3-f][1-10]-phenanthroline (DPQ), dipyrido-[3,2-a:2′3′-c]-phenazine (DPPZ)) the respective six-coordinated complexes are obtained. The introduction of bidentate ligands naturally results in the cis-position of dioxolene ligands in the tin coordination sphere. The possibility of intramolecular ligand–ligand charge transfer (LL′CT) between catecholate and diimine moieties in the synthesized octahedral metal derivatives is shown by electronic absorption spectroscopy. The effect of substituents in catecholate ligands and acceptor properties of diimines on the shift of a long-wave absorption band is determined. The electronic transition corresponding to LL′CT is revealed to undergo a bathochromic shift in the electronic absorption spectrum with a decrease in the polarity of the solvent used. [ABSTRACT FROM AUTHOR]

Palladium(II) complexes of the general formula [Pd(η3-C3H5)(L)](PF6), where L is 4,7-diphenyl-1,10-phenanthroline (1), 2,9-dimethyl-1,10-phenanthroline (2), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (3), 5-methyl-1,10-phenanthroline (4), 3,4,7,8-tetramethyl-1,10-phenanthroline (5), and 2-(2′-pyridyl) quinoxaline (6), were synthesized and characterized using high-resolution ESI-MS, NMR techniques and, in the case of (6), single-crystal X-ray diffraction methods. In addition, their photophysical properties were investigated. Complexes (1)–(6) were emitted in the greenish-blue region, with those containing methyl-substituted phenanthrolines having the higher quantum yield (≈14%) in the solid state. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) are a prominent class of organic materials constructed from versatile building blocks via reversible reactions. The quality of imine-linked COFs can be improved by using amine monomers protected with benzophenone forming benzophenone imines. Here, we present a study on substituted benzophenones in COF synthesis via formal transimination. 12 para-substituted N-aryl benzophenone imines, with a range of electron-rich to electron-poor substituents, were prepared and their hydrolysis kinetics were studied spectroscopically. All substituted benzophenone imines can be employed in COF synthesis and lead to COFs with high crystallinity and high porosity. The substituents act innocent to COF formation as the substituted benzophenones are cleaved off. Imines can be tailored to their synthetic demands and utilized in COF formation. This concept can make access to previously unattainable, synthetically complex COF monomers feasible. [ABSTRACT FROM AUTHOR]

An efficient and simple one‐pot synthesis of structurally diverse novel tetrahydroquinoline‐fused iminosugars was developed through the aza‐Diels‐Alder mechanism. The adaptability of this method has been demonstrated by a variety of imines and d/l‐ribose tosylates, and both, electron‐donating and ‐withdrawing substituted imines proceed well. In addition, this reaction is characterized by simple operation, good yield, and high atom economy. Some synthetic iminosugars showed moderate anti proliferation of HCT116 tumor cells. [ABSTRACT FROM AUTHOR]

Due to its high electron affinity and electron mobility in a wide absorption range of the visible solar spectrum, [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) is often used as an efficient acceptor in organic photovoltaics. In turn, imines are additives to the active layer of organic solar cells, mainly due to the free electron pair of the imine nitrogen atom and the presence of various chemical groups affecting the polarity and conformations of molecules. However, the attainable efficiency is not as high as expected. Therefore, we have systematically investigated two imines and their mixtures with PC71BM by spectroscopic (the high pressure UV–Vis and frequency domain dielectric), thermoelectric, and mechanical methods for organic, flexible photovoltaics. Both the imines, (N,NʹE,N,NʹE)-N,Nʹ-([2,2ʹ:5ʹ,2ʺ-terthiophene]-5,5ʺ-diylbis(methanylylidene))bis(benzo[d]thiazol-2-imine) (SC3) and (6E)-N-((5-(5-(5-((E)-(4-(4-(4-fluorophenyl)thiazol-2-yl)phenylimino)methyl)thiophen-2-yl)thiophen-2-yl)thiophen-2-yl)methylene)-4-(4-(4-fluorophenyl)thiazol-2-yl)benzenamine (SC13), have the same core composed of three thiophene rings but different terminal chains of the molecules. In the imine SC3, the imine bond is followed by benzothiazole rings on both sides of the core, while in SC13, a thiazole ring separates two benzene rings, the terminal one F-substituted. The difference in molecular structure affects the electric properties of the neat imine and its mixed layers. An addition of PC71BM to the imines improves their electric conductivity. The mechanical studies focused on the stress at break and elongation showed superior behaviour compared to fullerene derivative. High pressure systematically reduces the band gap energy, Eg, from 1.68 eV at 0.16 GPa to 1.51 eV at 2.69 GPa for PC71BM, from 1.77 eV at 0.1 MPa to 1.53 eV at 4.15 GPa for SC3, and from 1.99 eV at 0.11 GPa to 1.8 eV at 3.10 GPa for SC13, as determined by the UV–Vis absorbance measurements in a diamond-anvil cell. These Eg reductions reflect the compressed intermolecular interactions that can be used to monitor the structural stability of these compounds. Based on the dielectric studies it was found that the relaxation processes registered for both imines are probably the grain boundary relaxation. Two processes also appear in the systems with PC71BM, but none of them is the one characteristic of imines. The high-frequency process has a dipole character while the low-frequency one is probably the grain boundary relaxation of these systems. The mechanism of quasi-DC conduction in various temperature ranges in the studied systems was also determined. [ABSTRACT FROM AUTHOR]

A synthetic method to prepare 1-alkyl-substituted-pyrazolidin-3-ones efficiently that relies on the 4CzPN-mediated alkylation of azomethine imines by 4-alkyl-substituted-1,4-dihydropyridines (DHPs) under blue light emitting diode (LED) light (λmax = 456 nm) is reported. An approach that exploits the ability of blue LED light to initiate the acylation of the imine substrate by 4-acyl-substituted-DHPs to give 1-acyl-substituted-pyrazolidin-3-ones is also presented. Achieved under mild reaction conditions at room temperature, the synthetic protocol was shown to tolerate a broad range of functional groups to afford the corresponding 1-substituted-pyrazolidin-3-ones in yields up to 99%. [ABSTRACT FROM AUTHOR]

Reactions between imines and tungsten alkylidyne complexes are studied. The trianionic pincer ligand supported alkylidyne [tBuOCO]WCC(CH3)3(THF)2 (1) reacts with N-(R)-1-phenylmethanimine (PMI-R, R = Me, Ph, Bn, and TMS) yielding [tBuOC(H)O]W(η2-tBuC≡CPh)N(R) (4-R), products from metathesis reaction. In contrast, the non-pincer alkylidyne (tBuO)3W≡CC(CH3)3 does not react with PMI-R imines. [ABSTRACT FROM AUTHOR]

Using a formate salt as a promising hydrogen carrier and one-carbon (C1) source, we have developed a novel and practical method for the preparation of α-amino acid derivatives under mild conditions. In this approach, the photoexcited naphthalene thiolate acts simultaneously as a photoexcited single-electron reductant and a hydrogen atom transfer (HAT) catalyst, enabling efficient metal-free radical–radical cross-coupling of formate with ketimines and aldimines. [ABSTRACT FROM AUTHOR]

The imine bond is among the most applied motifs in dynamic covalent chemistry. Although its uses are varied and often involve coordination to a transition metal for stability, mechanistic studies on imine exchange reactions so far have not included metal coordination. Herein, we investigated the condensation and transimination reactions of an Fe2+‐coordinated diimine pyridine pincer, employing wB97XD/6‐311G(2d,2p) DFT calculations in acetonitrile. We first experimentally confirmed that Fe2+ is strongly coordinated by these pincers, and is thus a justified model ion. When considering a four‐membered ring‐shaped transition state for proton transfers, the required activation energies for condensation and transimination reaction exceeded the values expected for reactions known to be spontaneous at room temperature. The nature of the incoming and exiting amines and the substituents on the para‐position of the pincer had no effect on this. Replacing Fe2+ with Zn2+ or removing it altogether did not reduce it either. However, the addition of two ethylamine molecules lowered the energy barriers to be compatible with experiment (19.4 and 23.2 kcal/mol for condensation and transimination, respectively). Lastly, the energy barrier of condensation of a non‐coordinated pincer was significantly higher than found for Fe2+‐coordinating pincers, underlining the catalyzing effect of metal coordination on imine exchange reactions. [ABSTRACT FROM AUTHOR]

Imines play a fundamental role in organic synthesis and some of them have been detected in space. However, the simplest imines are spectroscopically not well-characterized. Herein we present the infrared and UV/Vis spectroscopic characterization of 2-iminoacetaldehyde using cryogenic matrix isolation techniques. After UV irradiation of 2-azidoacetaldehyde in solid argon at 3 K we identified two conformers of 2-iminoacetaldehyde, which can be photochemically interconverted. Deuterium labelling experiments and high level ab initio coupled cluster calculations at the CCSD(T)/CBS level of theory provide further evidence for the formation of 2-iminoacetaldehyde. [ABSTRACT FROM AUTHOR]

Secondary phosphine oxides R2P(O)H are a relatively stable tautomeric form of secondary phosphinous acids R2P–OH that with imine/iminium species, or their donors, form compounds with a P(O)–Csp3–N linkage (the phospha-Mannich reaction). These can be referred to as (α-aminoalkyl)phosphine oxides, (α-phosphinoylalkyl)amines, or P(O),N-acetals. Compared to P–Csp3–N linkages of P,N-acetals, products of phospha-Mannich reactions involving secondary phosphines R2PH, the P(O)–Csp3–N linkage is significantly more stable that allows for many examples of α-functionalized P(O),N-acetals and α-phosphinoylated N-heterocycles, whereas such examples for P,N-acetals are rare. Trivalent derivatives of phosphinous acids such as halides R2P–Hal, esters R2P–OR' (phosphinites), amides R2P–NR'2 (aminophosphines), and phosphides R2P–PR'2 (biphosphines) also participate in Mannich-type reactions with mechanisms depending on the reactants. The phosphinous halides and esters react with (α-alkoxyalkyl)amines (N,O-acetals) and (α-haloalkyl)amines (N,Hal-acetals), respectively, via Arbuzov-type intermediates that are rearranged into P(O),N-acetals and alkyl halides (Arbuzov rearrangement). Furthermore, unlike phospha-Mannich reactions involving phosphines, secondary phosphine oxides and P(O),N-acetals are less sensitive to oxidation, and imines/iminium species can be generated not only under conventional Mannich conditions, i.e., from N,E-acetals (E = OH, O, N, halogen, etc.), but also, for example, by oxidation of α-C-atom of amines, or by oxidation of alcohols to aldehydes that than form imines/iminium species with amines. [ABSTRACT FROM AUTHOR]

Nonheme iron oxygenases utilize dioxygen to accomplish challenging chemical oxidations. A further understanding of the Fe-O2 intermediates implicated in these processes is challenged by their highly transient nature. To that end, we have developed a ligand platform featuring phosphinimide donors intended to stabilize oxidized, high-spin iron complexes. O2 exposure of single crystals of a three-coordinate Fe(II) complex of this framework allowed for in crystallo trapping of a terminally bound Fe-O2 complex suitable for XRD characterization. Spectroscopic and computational studies of this species support a high-spin Fe(III) center antiferromagnetically coupled to a superoxide ligand, similar to that proposed for numerous nonheme iron oxygenases. In addition to the apparent stability of this synthetic Fe-O2 complex, its ability to engage in a range of stoichiometric and catalytic oxidation processes demonstrates that this iron-phosphinimide system is primed for development in modeling oxidizing bioinorganic intermediates and green oxidation chemistry.

Density functional theory computations have elucidated the mechanism and origins of stereoselectivity in McGlacken's aldol-Tishchenko reaction for the diastereoselective synthesis of 1,3-amino alcohols using Ellman's t-butylsulfinimines as chiral auxiliaries. Variations of stereochemical outcome are dependent on the nature of the ketone starting materials used, and the aspects leading to these differences have been rationalized. The intramolecular hydride transfer step is the rate- and stereochemistry-determining step, and all prior steps are reversible.

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.

A highly enantioselective Michael addition between benzophenone-imine of glycine esters and β-substituted α,β-unsaturated pyrazolamides has been realized by using 10 mol% of a chiral cyclopropenimine (Lambert catalyst, CSB-1) as an organosuperbase catalyst under very mild conditions to afford Michael adducts in up to 95% yield and 99% ee. The pyroglutamic acid esters with two adjacent stereocenters are obtained through subsequent lactamization in quantitative yields and excellent enantioselectivities. [ABSTRACT FROM AUTHOR]

The reductive coupling of dienol ethers with N-tosylimines catalyzed by Ni(0) in the presence of a VAPOL-derived phosphoramidite ligand follows an unprecedented regiochemical course; it furnishes syn-configured 1,2-aminoalcohol derivatives in good chemical yields with up to 94% ee. [ABSTRACT FROM AUTHOR]

An unprecedented enantioselective organocatalytic spirocyclization strategy is presented by in situ generation of aminoisobezofulvenes. The reaction sequence involves a reductive Michael/aldol‐condensation/Michael addition cascade by iminium‐enamine catalysis. The key success of this spirocyclization was the formation of intermediatory nucleophilic aminoisobenzofuvenes accountable for intramolecular Michael addition. Benzospirononanes featuring an all carbon qauternary spirocenter were obtained using proline‐derived amino‐organocatalyst in moderate to good yields and excellent diastereo‐ and enantioselectivities (up to >20 : 1 dr, and 99 % ee). Post‐methodological manipulation of benzospirononanes was also demonstrated. [ABSTRACT FROM AUTHOR]

The reduction in esters, nitriles, and imines requires harsh conditions (highly reactive reagents, high temperatures, and pressures) or complex metal-ligand catalytic systems. Catalysts comprising earth-abundant and less toxic elements are desirable from the perspective of green chemistry. In this study, we developed a green hydroboration protocol for the reduction in esters, nitriles, and imines at room temperature (25 °C) using pinacolborane as the reducing agent and a commercially available Grignard reagent as the catalyst. Screening of various alkyl magnesium halides revealed MeMgCl as the optimal catalyst for the reduction. The hydroboration and subsequent hydrolysis of various esters yielded corresponding alcohols over a short reaction time (~0.5 h). The hydroboration of nitriles and imines produced various primary and secondary amines in excellent yields. Chemoselective reduction and density functional theory calculations are also performed. The proposed green hydroboration protocol eliminates the requirements for complex ligand systems and elevated temperatures, providing an effective method for the reduction in esters, nitriles, and imines at room temperature. [ABSTRACT FROM AUTHOR]

The synthesis and properties of photoswitchable electron-rich phosphines containing N-heterocyclic imines equipped with a photochromic dithienylethene unit are reported. Heteronuclear NMR spectroscopy and UV/vis studies reveal that the imine substituents undergo reversible electrocyclic ring-closing and ring-opening reactions upon exposure to UV and visible light, respectively. The photoisomerization alters the electron-donating ability of the phosphines by up to ΔTEP = 8 cm−1. [ABSTRACT FROM AUTHOR]

Despite p-block clusters being known for over a century, their application as catalysts to mediate organic transformations is underexplored. Here, the boron functionalized [P7] cluster [(BBN)P7]2- ([1]²-; BBN = 9-borabicyclo[3.3.1]nonane) is applied in the dearomatized reduction of pyridines, as well as the hydroboration of imines and nitriles. These transformations afford amine products, which are important precursors to pharmaceuticals, agrochemicals, and polymers. Catalyst [1]2- has high stability in these reductions: recycling nine times in quinoline hydroboration led to virtually no loss in catalyst performance. The catalyst can also be recycled between two different organic transformations, again with no loss in catalyst competency. The mechanism for pyridine reduction was probed experimentally using variable time normalization analysis, and computationally using density functional theory. This work demonstrates that Zintl clusters can mediate the reduction of nitrogen containing substrates in a transition metal-free manner. [ABSTRACT FROM AUTHOR]

A strategy that combines electrochemical synthesis and photoredox catalysis was reported for the efficient synthesis of imines. This approach was demonstrated to be highly versatile in producing various types of imines, including symmetric and unsymmetric imines, by exploring the impact of different substituents on the benzene ring of the arylamine. Additionally, the method was specifically applied to modify N‐terminal phenylalanine residues and was found to be successful in the photoelectrochemical cross‐coupling reaction between NH2‐Phe‐OMe and aryl methylamines, leading to the synthesis of phenylalanine‐containing imines. Therefore, this technique would present a convenient and efficient platform for synthesizing imines, with promising applications in chemical biology, drug development, and organic synthesis. [ABSTRACT FROM AUTHOR]

A highly enantioselective cyanation of imines (up to >99 % ee) has been developed using well‐designed C2‐symmetric hydrogen bonding catalysts. The catalytic strategy was characterized with low catalyst loading (0.1–1 mol %), easily accessible catalysts with diverse functional groups, and catalytic base additives. A wide range of imines, including the challenging N‐Boc and N‐Cbz protected ketimines and aldimines, as well as fluoroalkylated ketimines, were investigated under mild conditions to afford the products with good to excellent yields (up to 99 % yield) and high enantioselectivity (up to >99 % ee). Control experiments revealed that the multiple hydrogen bonding catalysts enhanced the reactivity and enantioselectivity of the Strecker reaction initiated by the base. [ABSTRACT FROM AUTHOR]

The Schiff base reaction of imidazole-2-carboxaldehydes with the anion of alanine, leucine and phenylalanine in the presence of nickel(II) ion gives the neutral NiL2 complexes. The Schiff base ligand, L, binds through an imidazole nitrogen, NIm, the amino acid nitrogen, NAA, and a carboxylate oxygen, O, atom. The two N2O ligands bind to the nickel(II) in a meridional fashion with the NIm and O of each ligand in trans positions. These ligands can exist as the anticipated aldimine, Im − CH = NAA − CH(R) − CO2−, or the ketimine, Im − CH2NAA = C(R) − CO2−, tautomer. Tautomerization of the initially formed aldimine Schiff base results in movement of the hydrogen atom of the alpha carbon of the amino acid to the aldehyde carbon, CAld, atom of the imidazole carboxaldehyde with resultant relocation of the imine double bond in the reverse direction. Ten structures of the structurally unprecedented ketimine tautomer, prepared from imidazole-2-carboxaldehydes and a pyrazole-3-carboxaldehyde, were presented. The structural data supported the formation of the ketimines in each case, while the aldimine tautomer was observed with imidazole-4-carboxaldehydes. A rationale of this can be explained on the basis of charge distribution in the likely intermediate in the tautomerization. [ABSTRACT FROM AUTHOR]

A synthesis of a novel series of cis-2-azetidinones 2a-c was carried out by the cycloaddition reaction of imine 1a-c and chloroacetyl chloride in dry dichloromethane at 0-5 °C using triethylamine. The cycloaddition of the Schiff bases with chloroacetyl chloride resulted in the corresponding major product cis-2-azetidinone stereoisomers 2a-c. The synthesized compounds were characterized by analytical and spectral techniques (infrared, ¹H NMR, 13C NMR, and elemental analysis). [ABSTRACT FROM AUTHOR]

In this study, two innovative hydrazine-hydrazone ligands were synthesized through the chemical reaction involving the isatin moiety with 4-hydroxybenzohydrazide and salicyloylhydrazine. Subsequent to the synthesis of these ligands, Cu(II) complexes were meticulously prepared, and their molecular structures were comprehensively analyzed utilizing an array of spectroscopic techniques. Furthermore, the crystallographic investigation was employed to elucidate the precise crystal structure of the Cu(L²)2 complex, incorporating the salicyloylhydrazine moiety. The research focuses on investigating the cytotoxic effects of Cu(II) complexes bearing isatine groups on cancer cells. These complexes were tested against lung carcinoma (A549) and breast carcinoma (MCF-7) cell lines using the MTT assay, with cisplatin as a positive control. Additionally, their effects on human normal cell line 3T3 were assessed. The Cu(L¹)2 complex exhibited significant inhibitory effects on tumor cells in a dose-dependent manner, although not as potent as cisplatin. The cytotoxic selectivity indices (SI) indicated acceptable selectivity levels for both cancer cell lines, indicating potential for selective lethality. The crystal structure of one compound was confirmed, revealing van der Waals interactions and hydrogen bonding in the packing. [ABSTRACT FROM AUTHOR]

We have built an autocatalytic reaction network, based on the hydrolysis of certain imines, which exhibits bistability in an open system. The positive feedback originates from the interplay of fast acid–base equilibria, leading to hydroxide ion production, and pH-dependent hydrolysis rates. The addition of a first-order removal of the autocatalyst can result in sustained pH oscillations close to physiological conditions. The unit-amplitude pH oscillations are accompanied by the stoichiometric conversion of imine into amine back and forth. A systematic parameter search is carried out to characterize the rich observable dynamics and identify the evolving bifurcations. [ABSTRACT FROM AUTHOR]

Graphene is one of the amazing present encroachments in current research area of science and one of the utmost fascinating materials for relevance in cutting-edge research. Herein, we designed lemon-derived heteroatoms-doped graphene quantum dots (S, N-GQDs) based photocatalyst for the first time. For the integrating reactions of amines in aerobic conditions under solar light by S, N-GQDs photocatalyst exhibit utmost higher photocatalytic activity than simple oxygen-doped graphene quantum dots (O-GQDs) due to slow recombination charges. The mechanisms accountable for the drastically increased photocatalytic activity of S, N-GQDs in solar light responsive integrating reactions of amines in aerobic conditions into the corresponding derivative of imines are also completely scrutinized. [ABSTRACT FROM AUTHOR]

The use of Pd(OAc)2 as catalyst for the challenging synthesis of imines through acceptorless alcohol dehydrogenation using secondary alcohols and amines is reported. The reaction requires low catalyst loading, shows high selectivity for the formation of the imine without the need of adding any base or additive, and can be scaled up. Interestingly, when the catalytic reaction is performed in a closed system, in the presence of base, the reaction selectively yields the corresponding amine. To highlight the practical utility of the synthesis of imines, a family of structurally important scaffold, an indole, were synthesized. [ABSTRACT FROM AUTHOR]