Intramolecular Redox Reaction Research Articles

C[sbnd]C rupture in key monosaccharides and succedent redox in supercritical ethanol

The valorisation of biomass is crucial to establish a sustainable society and reduce the over dependence on fossils. On the other hand, the origins of fossils were both inorganic and organic including biomass, which contains organic substances found in nature and undergoes a series of natural evolutions, where the most common substance in biomass decay is ethanol. Here we report the conversion of biomass derived xylose, fructose, and glucose in supercritical ethanol to simulate the natural processes under specific conditions. Through both theoretical simulation and experiments including 13C-labeled reaction with NMR, we found that CC breakage and self-redox reactions occurred obtaining a variety of functional molecules like ethyl lactate, ethyl glycolate, 1,1-diethoxyethane, etc. without other catalyst. Ethanol acted simultaneously as solvent, catalyst, and reactant. The increased reversible ionization of ethanol under supercritical conditions produced much higher concentration of CH3CH2O– and CH3CH2OH2+, where the basic CH3CH2O– priorly catalysed the isomerization and Cα-Cβ cleavages of both the monosaccharides and derived intermediates, as well as the intermolecular and/or intramolecular Cannizzaro redox reactions, whereas the acetic CH3CH2OH2+ catalysed the dehydration, acetal reaction, etc. This study provides mechanistic clues to understand the origin of fossil and to take new biorefinery strategies.

Synthesis of N-Glyoxylyl Peptides Enabled by a Lossen Rearrangement-Induced Intramolecular Redox Reaction of N-Terminal Glycyl Hydroxamic Acid.

An oxidant-free approach to the synthesis of N-glyoxylyl peptides has been developed that utilizes the Lossen rearrangement of the N-terminal glycyl hydroxamic acid residue. The synthesis proceeds via an intramolecular redox mechanism to yield the glyoxylyl peptides, which are then subjected to various peptide cyclization procedures. The reaction scheme is suitable for oxidation-sensitive moieties including amino acids.

Synthesis of Organofluorine Compounds with Acylsilanes†

Comprehensive SummaryOrganofluorine compounds are central in synthetic chemistry, medicinal chemistry and material chemistry. In this review, we summarize the investigations on the synthesis of organofluorine compounds with acylsilanes. For the non‐fluorinated acylsilanes, the in situ generation of difluoroenoxysilanes from the reactions of the acylsilanes with trifluoromethylation reagents is the major pathway, leading to the facile preparation of various α,α‐difluoroketones. For the fluoroalkylacylsilanes, apart from the in situ generation of difluoroenoxysilanes through anion Brook rearrangement, radical Brook rearrangement of the photoexcited acylsilanes and the selective control of reactivities of the biradicals pave the way for the synthesis of a variety of organofluorine compounds. In general, most of these reactions gave racemic products, and the asymmetric synthesis of organofluorine compounds with acylsilanes is still rare, which would be a future direction of this field. Key ScientistsIn 1957, the first acylsilane compound, triphenylsilyl phenyl ketone was reported by Brook group. In 1991, Portella and coworkers reported the reaction of non‐fluorinated acylsilanes and perfluoroorganometallic reagents without Brook rearrangement, resulting in the formation of alcohols as the products. In 1992, Xu and coworkers carried out the first investigation on fluoroalkylacylsilanes for the preparation of difluoroenoxysilanes through anion Brook rearrangement. In 1994, Portella group reported the synthesis of difluoroenoxysilanes with non‐fluorinated acylsilanes and Ruppert‐Prakash reagent. In 2009, Otaka and coworkers reported a NHC‐mediated intramolecular redox reaction to prepare (Z)‐fluoroalkene dipeptide isosteres (FADIs) from γ,γ‐difluoro‐α,β‐ enoylsilane. Until 2022, the application of radical Brook rearrangement of fluoroalkylacylsilanes for the generation of fluoroalkylsiloxycarbenes was achieved by Shen group, enabling the synthesis of fluoroalkylated cyclopropenols. In 2022, Shen and coworkers successfully achieved the trapping of biradical intermediates generated from fluorine‐containing acylsilanes, leading to the facile preparation of fused gem‐difluorooxetanes. In the same year, Shen group reported the first asymetric reactions of fluoroalkylacylsilanes to prepare enantiomerically enriched fluoroalkyl alcohols and difluoroenoxysilanes.

Silver(I) complexes with phenolic Schiff bases: Synthesis, antibacterial evaluation and interaction with biomolecules.

Novel Ag(I) complexes (2a–2c) with phenolic Schiff bases were synthesized using 4,6-di-tert-butyl-3-(((5-mercapto-1,3,4-thiadiazol-2-yl)imino)methyl)benzene-1,2-diol (1a), 4,6-di-tert-butyl-3-(((4-mercaptophenyl)imino)methyl)benzene-1,2-diol (1b), and 4,6-di-tert-butyl-3-(((3-mercaptophenyl)imino)methyl)benzene-1,2-diol (1c). They were examined by elemental analysis, FT-IR, UV-Vis, 1H-NMR spectroscopy, XRD, cyclic voltammetry, conductivity measurements, and biological methods. The complexes are characterized by distorted geometry of the coordination cores AgN2S2 (2c), AgNS (2b) and AgS2 (2a). These stable complexes were not typified by the intramolecular redox reaction in organic solvents resulting in the formation of silver nanoparticles (AgNPs). Antibacterial activity of 1a–1c and 2a–2c was evaluated in comparison with AgNPs and commonly used antibiotics. All the complexes were more active than the ligands against the bacteria tested (14), but they were less active than AgNPs and commonly used antibiotics. Both 1a–1c and their complexes 2a–2c exhibited the capability for the bovine heart Fe(III)-Cyt c reduction. The ligands 1b and 1c were characterized by the highest reduction rate among the compounds under study, and they showed a higher reducing ability (determined by cyclic voltammetry) as compared with that of their Ag(I) complexes 2b and 2c.

Intramolecular redox cyclization reaction access to cinnolines from 2-nitrobenzyl alcohol and benzylamine via intermediate 2-nitrosobenzaldehyde.

A transition-metal-free intramolecular redox cyclization reaction for the synthesis of cinnolines has been developed from 2-nitrobenzyl alcohol and benzylamine. Mechanistic investigations disclosed the involvement of a key intramolecular redox reaction, followed by condensation, azo isomerization to hydrazone, cyclization, and aromatization to form the desired products. Notably, the formation of intermediate 2-nitrosobenzaldehyde and (E)-2-(2-benzylidenehydrazineyl) benzaldehyde plays an important role in this transformation.

Divergent Synthesis of Substituted Amino-1,2,4-triazole Derivatives

AbstractA divergent efficient assembly of disubstituted 1,2,4-triazoles was established by cyclization of readily accessible N′-nitro-2-hydrocarbylidene-hydrazinecarboximidamides with moderate to excellent yields under mild reaction conditions. This divergent synthetic strategy was achieved simply by varying the reaction conditions. Under acidic conditions, amino-1,2,4-triazoles were obtained by an intramolecular redox reaction involving the NO2 group. Control experiments and DFT studies revealed that this transformation proceeds via an intramolecular 1,3-hydride transfer pathway leading to HNO2 elimination. Under neutral conditions with water as the solvent, nitroimino-1,2,4-triazoles were obtained by oxidative intramolecular annulation under air.

Copper-assisted oxidation of catechols into quinone derivatives.

Catechols are ubiquitous substances often acting as antioxidants, thus of importance in a variety of biological processes. The Fenton and Haber–Weiss processes are thought to transform these molecules into aggressive reactive oxygen species (ROS), a source of oxidative stress and possibly inducing degenerative diseases. Here, using model conditions (ultrahigh vacuum and single crystals), we unveil another process capable of converting catechols into ROSs, namely an intramolecular redox reaction catalysed by a Cu surface. We focus on a tri-catechol, the hexahydroxytriphenylene molecule, and show that this antioxidant is thereby transformed into a semiquinone, as an intermediate product, and then into an even stronger oxidant, a quinone, as final product. We argue that the transformations occur via two intramolecular redox reactions: since the Cu surface cannot oxidise the molecules, the starting catechol and the semiquinone forms each are, at the same time, self-oxidised and self-reduced. Thanks to these reactions, the quinone and semiquinone are able to interact with the substrate by readily accepting electrons donated by the substrate. Our combined experimental surface science and ab initio analysis highlights the key role played by metal nanoparticles in the development of degenerative diseases.

Biomimetic alloxan-catalyzed intramolecular redox reaction with O2: One-pot atom-economic synthesis of sulfinyl-functionalized benzimidazoles

Given the necessity of sacrificial reductants in various biomimetic aerobic oxygenations, alloxan-catalyzed aerobic redox system for one-pot atom-economic synthesis of sulfinyl-functionalized benzimidazoles was developed by ingeniously binding both the substrate sulfide and sacrificial reductant. This mild and transition-metal-free protocol undergoes two oxidations without additional sacrificial reagents, except for the environmentally benign molecular oxygen.

Copper-catalyzed intramolecular redox reaction: Asymmetric synthesis of chiral 2-(1H-pyrrol-1-yl)-mandelic acid esters

An efficient approach to chiral α-hydroxy acid esters by Lewis acid-mediated asymmetric [1,5]-hydride shift and isomerization of 2-(3-pyrroline-1-yl)arylketone acid ester has been achieved in up to 96% yield and 94% ee. This protocol would be applied in the synthesis of chiral α-hydroxy acid derivatives with simplicity and high enantioselectivity.

Effects of halogen substitution on the photostability and thermal degradation of boron(III), zinc(II) and cadmium(II) dipyrrinato complexes

The results of investigation of the photostability and thermal degradation of B(III), Zn(II), Cd(II) complexes with monoiodo- and dibromosubstituted dipyrrins of the composition [BF2L] and [ML2] were presented. The processes of photo- and thermal degradation of complexes includes the initial stages of dye molecules dehalogenation. In general, the replacement of 4-iododipyrrin ligand by 5,5′-dibromo- and 4,4′-dibromosubstituted analogs in the composition of complexes [BF2L] and [ML2] promotes an increase in the photo- and thermal stability of the dyes. The replacement of the saturate hydrocarbon (cyclohexane) with the aromatic analogue (benzene) leads to a significant decrease in the photostability of [BF2L] and [ML2] because of polarization of the chromophore systems of dye molecules due to π-π stacking with aromatic solvent molecules. The thermal destruction start temperatures [ML2] and [BF2L] in the argon atmosphere range from 179 to 275 °C and strongly depend on the nature and efficiency of the participation of complexing and halogen atoms in intramolecular redox reactions. Complexes [BF2L], which showed the greatest photostability in solutions, differ the least thermal stability in the solid phase. The observed differences are due to the specific structural effects and different mechanisms of the photo- and thermal degradation processes under various environmental conditions.

Oxidation of the 14-Membered Macrocycle Dibenzotetramethyltetraaza[14]annulene upon Ligation to the Uranyl Ion.

Reaction of Li2(tmtaa) (tmtaaH2 = dibenzotetramethyltetraaza[14]annulene) with 1 equiv of [UO2Cl2(THF)3], in an attempt to form cis-[UO2(tmtaa)], affords the bis(uranyl) complex [Li(THF)3][Li(THF)2][(UO2Cl2)2(tmtaa)] (1) as a red-brown crystalline solid in modest yield. Complex 1 can be synthesized rationally by reaction of Li2(tmtaa) with 2 equiv of [UO2Cl2(THF)3]. Under these conditions, it can be isolated in 44% yield. In the solid state, complex 1 features two [UO2Cl2] fragments that are bridged by a highly puckered (tmtaa)2- ligand. Both uranyl fragments feature normal uranyl metrical parameters (U-O (av.) = 1.78 Å, O-U-O = 176.8(3)° and 178.0(3)°). The most notable structural feature of 1, however, is the presence of a lithium cation that coordinates to an oxo ligand from each uranyl fragment. In contrast to the Li2(tmtaa) reaction, addition of [K(DME)]2[tmtaa] to 1 equiv of [UO2Cl2(THF)3] results in formation of the 2e- oxidation products of (tmtaa)2-. Three isomers of C22H22N4 (compounds 2, 3, and 4) were isolated as a mixture of orange crystals in 41% combined yield. All three isomers were characterized by X-ray crystallography. We hypothesize that these ligand oxidation products are formed upon decomposition of the unobserved cis uranyl intermediate, cis-[UO2(tmtaa)], which undergoes a facile intramolecular redox reaction.

Intramolecular photoredox reactions of 1,2-naphthoquinone derivatives

Photoirraditation of substituted 1,2-naphthoquinones gives the corresponding oxacycle via intramolecular redox reaction, which enabled net CH functionalization of the proximal position to the excited carbonyl group of the quinones. The substrate scope and mechanistic insights are described.

Intramolecular Photoredox Reaction of Naphthoquinone Derivatives

Photoinduced intramolecular redox reaction of naphthoquinone derivatives is described, enabling C–H bond oxygenation at the α-position of the quinone nucleus and the quinone reduction under photoirradiation. The substrate scope and mechanistic insight are reported.

Synergistic and Antagonistic Ligand Effects in the Transformation of Silver Compounds of Keto‐ and Cyano‐Functionalised Oximates and Nitronates: A Systematic Study Using Thermal Analysis

Molecular silver compounds are target precursor molecules for the deposition of silver films from solution. The thermal decomposition of silver complexes of nitro and nitroso derivatives of malononitrile, cyanoacetamide and methyl cyanoacetate as well as with nitroacetamide and methyl nitroacetate was investigated for the first time in a systematic manner. The analysis of the evolving gases by means of infrared spectroscopy or mass spectrometry revealed that intramolecular redox reactions had a significant impact on the reaction mechanism, in particular the interactions of the nitro and nitroso functionalities with amido and ester groups. The studied ligands bearing cyano groups typically lead to the intermediary formation of silver cyanide, whereby metallic silver is formed only at higher temperatures. Silver complexes of nitroacetamide and methyl nitroacetate, however, undergo decomposition to metallic silver at temperatures already below 200 °C. Thin films of silver on glass substrates could be synthesised by spincoating of these precursors and subsequent annealing. Higher conversion temperatures lead to more uniform surface coverage and lower film roughness.

ChemInform Abstract: Catalysis Application of Metal (Rh, Ir) Quinonoid Complexes

AbstractReview: 45 refs.

Intramolecular redox reaction for the synthesis of N-aryl pyrroles catalyzed by Lewis acids.

An efficient approach to synthesize N-aryl pyrroles via Lewis acid-mediated 1,5-hydride shift and isomerization of 2-(3-pyrroline-1-yl)arylaldehydes has been achieved in up to 89% yield. This methodology is applicable to the synthesis of fluorazene derivatives as electron donor (D)/acceptor (A) molecules.

Synthesis, structures and stability of amido gold(iii) complexes with 2,2':6',2''-terpyridine.

Three gold(iii) complexes with terminal amido ligands were prepared by the reaction of [Au(III)(trpy)(OH)](ClO4)2 and primary amines having electron-withdrawing groups such as 2-amino-4-chloropyrimidine, 2-amino-5-chloro-pyridine, and 2-aminopyrimidine. Conversion of the amido ligands into the imido or amine ligands resulted in the decomposition of the complexes by intramolecular redox reaction or the release of amine ligands, respectively.

Polyoxotungstates in Molecular Boxes of Purine Bases

Three new compounds, (GuaH)4[W10O32](H2O)4 (1), (ThbH)3(H3O)[(W10O32](H2O)7.5 (2) and (ThbH)2[W6O19](H2O)2 (3) (GuaH = guaninium, thbH = theobrominium) were synthesized in acidified acetonitrile solutions. The polyoxotungstates in all of these compounds are surrounded by an organic matrix consisting of protonated purine bases and water molecules. The distinctive structural arrangement of the aromatic organic cations around the polyoxoanions parallel to their faces is reminiscent of nanosized boxes. The results of IR spectroscopy are consistent with previously reported results for polyoxotungstates and neat organic compounds. The polyoxoanions are reduced to tungsten(IV) oxide upon heating over 400 °C in an intramolecular redox reaction.

Hexa‐ to Octamolybdate Rearrangement leads to the New Coordination Polymer [Ag(PhCN)(thb)]4[β‐Mo8O26](PhCN)2

AbstractPolyoxomolybdates tend to re‐agglomerate to β‐octamolybdate upon reaction with Ag+ under hydrothermal conditions and in organic solvents. Consistent with this tendency, a new coordination polymer [Ag(PhCN)(thb)]4[β‐Mo8O26](PhCN)2 (thb = theobromine) (1) was obtained and characterized by single crystal XRD, powder XRD, DTA/TG, IR, UV/Vis, and elemental analysis. 1 is a one‐dimensional coordination polymer, in which octamolybdate anions are joined by [Ag(PhCN)(thb)]+ cations along the crystallographic a axis. A firm network of intermolecular interactions, especially between self‐pairing thb ligands, interlinks these chains. Salt 1 is turned into MoO2 and Ag upon thermolysis in an intramolecular redox reaction.

Catalysis Application of Metal (Rh, Ir) Quinonoid Complexes

Many metal quinonoid complexes have been synthesized and studied due to their interesting properties. Quinonoid molecules can participate in proton-coupled inter-molecular redox reactions. By combining metals with quinonoid molecules, the resulting π-bonded metal complexes can experience proton-coupled intra-molecular redox process between metal and quinonoid molecules. As a result of these intra-molecular redox reactions, positive, neutral, and anionic π-bonded quinonoid metal complexes are reversibly formed and are isolated with relative ease. Many applications of metal quinonoid complexes have been studied relevant to coordination networks, nano-chemistry, surface chemistry, anti-cancer agents, and luminescent materials. Catalysis applications of metal quinonoid complexes had not been shown before 2005. New catalytic applications of π-bonded quinonoid rhodium complex are reviewed. In addition, both homogeneous and heterogeneous catalyses by metal (Rh, Ir) quinonoid complex are discussed.