Acid-Catalyzed Reaction of (4,4-Diethoxybutyl)ureas with Phenols as a Novel Approach to the Synthesis of α-Arylpyrrolidines

1-(4,4-Diethoxybutyl)-3-alkylureas undergo intramolecular cyclization in the presence of trifluoroacetic acid and various phenols, leading to the new N-alkyl-2-arylpyrrolidine-1-carboxamides with moderate to excellent yields. It was found that these compounds undergo spontaneous solid-phase epimerization at room temperature. Advantages of the proposed approach are mild reaction conditions and no need for expensive reagents or catalysts.     

Synthesis of 1-(2-Oxoalkyl)-2-acyltetrahydro-isoquinolines by α-Amidoalkylation of Methylene Active Carbonyl Compounds with N-Acyliminium Intermediates

Intermolecular α-amidoalkylation reaction of methylene active carbonyl compounds with N-acyliminium salts of 3,4-dihydroisoquinolines and acyl chlorides has been used for synthesis of 1-(2-oxoalkyl)-2-acyltetrahydroisoquinolines.     

Silica‐Supported bis (Trimethylsilyl) Chromate: Oxidation of Thiols to Their Corresponding Disulfides

An efficient and convenient method for the oxidation of thiols mediated by silica‐supported bis (trimethylsilyl) chromate (BTSC) in acetonitrile is reported.     

LC–ELISA as a contribution to the assessment of matrix effects with environmental water samples in an immunoassay for estrone (E1)

Accreditation and Quality Assurance - Estrone (E1), a metabolite of the estrogenic hormones 17β-estradiol (β-E2) and 17α-estradiol (α-E2), is itself a potent estrogen which can...     

High Diastereoselectivity in the Conjugate Addition of Functionalized Alcohols to a Chiral(E)-Nitroalkene

Nitr0alkenesareversatilesyntheticintermediatesaspowerfulelectron-deficientreactantsincycloadditionandconjugatadditionreacti0ntoproducealargevarietyfunctionalizedcarbocyclicrings'.Purthermore,thenitrogrouPcanbeconvertedintoawiderangeoffiinctionalities2-Al0ughDiels-Alderreaction3andcyclopropanationoffunctionalizedcarbonnucleophiles4toY-chiralnitr0alkenehavebeenreportedrecently.Sofarthedetailedresearch0ftheconjugateadditionsoffimctionalizedalcoholst0chira1nitf0keneshasn0tbeenreported.Herewewish…     

Silafunctional compounds in organic synthesis. 29.1 Oxidation of (alkenyl)alkoxysilanes to α-hydroxy ketones

(Alkenyl)alkoxysilanes are readily transformed into α-hydroxy ketones via epoxidation and the subsequent oxidative cleavage of the carbon—silicon bonds.     

Ceric Triethylammonium Nitrate [Ce(Et3NH)2l(NO3)6; An Efficient Oxidant for the Oxidation of Benzylic Alcohols and α-Hydroxy Ketones to Their Corresponding Carbonyl Compounds Under Mild Conditions

Ceric triethyl ammonium nitrate is prepared and used for the oxidation of benzylic alcohols, and α-hydroxy Retones to their corresponding carbonyl compounds in methylene chloride with high yields.     

Nickelatetrazoles as Intermediates in the Course of the Photolysis of Nickel(II) Azido Complexes? – A Theoretical Study

The primary photoreactions due to charge transfer excitation of d⁸ transition metal complexes of [MP₂(N₃)₂] constitution (P₂: mono‐ or diphosphane ligands) are strongly influenced by the central ion. While [MP₂(N₃)₂] complexes of both palladium(II) and platinum(II) yield primarily the corresponding metal(I) species and azidyl radicals, nickel(II) complexes of the same constitution lead to intermediate generation of nitrenes as has been indirectly shown by various scavenging reactions. During the course of the succeeding reactions, the intermediate generation of nickelatetrazoles is assumed. Both nitrene and metallatetrazole intermediates could not be identified directly so far. Therefore, the proposed reaction pathway has been modeled theoretically to get indications regarding the probability of the formation of such intermediates. Based on density functional theory (DFT) calculations, the energetics of the proposed pathway is compared with those of possible other pathways. The calculations support the proposed reaction pathway and point to possible reasons for the different behaviour of nickel(II) compared to palladium(II) and platinum(II).     

Synthesis of α, β-unsaturated γ-amino esters with unprecedented high (E)-stereoselectivity and their conformational analysis in peptides

Mild, efficient and racemization-free synthesis of N-protected α, β-unsaturated γ-amino esters with unprecedented high E- stereoselectivity is described. This method is found to be compatible with Boc-, Fmoc- and other side chain protecting groups. The crystal conformations of the vinylogous γ-amino esters in monomers and in homo- and mixed dipeptides are studied. Further, the vinylogous homo-dipeptide showed a β-sheet conformation, while mixed α- and α,β-unsaturated γ-hybrid dipeptide adapted an irregular structure in single crystals.     

Binuclear complexes with the “Chinese Lantern” geometry as intermediates in the liquid-phase oxidation of dibenzyl ether with atmospheric oxygen in the presence of copper(II) carboxylates

Reactions of copper(II) carboxylates with dibenzyl ether (DBE) gave binuclear complexes of the formula Cu₂(μ-OOCR)₄(DBE)₂ (R = Bu ^t , Ph, and CF₃). The complexes were characterized by X-ray diffraction. The axial positions in the lantern-type dimer are occupied by the coordinated DBE molecules. The complexes seem to be analogs of intermediate catalysts for the oxidation of DBE with atmospheric oxygen in the presence of transition metal complexes. When stored in air, the complex Cu₂(μ-OOCPh)₄(DBE)₂ underwent oxidation into Cu₂(μ-OOCPh)₄(HOOCPh)₂, which was characterized by X-ray diffraction. The geometry of its framework is similar; the structure is stabilized by intramolecular H bonds between the axially oriented benzoic acid molecules and the adjacent bridging benzoate anions.     

Fluorescence immunoassay of α-fetoprotein with iron(III) tetrasulfonatophthalocyanine as a mimetic enzyme labeling reagent

A new fluorimetric immunoassay for α-fetoprotein (AFP) has been developed using a novel promising mimetic peroxidase, iron(III) tetrasulfonatophthalocyanine (FeTSPc), as a labeling reagent to catalyze the fluorescence reaction of P- hydroxyphenylacetic acid (P-HPA) and hydrogen peroxide (H₂O₂). In the competitive immunoassay, anti-AFP antibody was coated on a 96-well plate (polystyrene) and a constant amount of FeTSPc-labeled AFP and a known amount of test solution were added. Non-labeled and FeTSPc-labeled AFP compete for binding to the plate-bound antibody. After the immunoreaction, the immunochemically adsorbed FeTSPc–AFP conjugate moiety was determined by measuring the fluorescence produced in a solution containing P-HPA and H₂O₂. AFP can be determined in the concentration range of 1–300 ng mL^–1 with a detection limit of 0.5 ng mL^–1. Received: 14 November 2000 / Revised: 29 December 2000 / Accepted: 15 January 2001     

Synthesis of Graphene Oxide by Oxidation of Graphite with Ferrate(VI) Compounds: Myth or Reality?

It is well established that graphene oxide can be prepared by the oxidation of graphite using permanganate or chlorate in an acidic environment. Recently, however, the synthesis of graphene oxide using potassium ferrate(VI) ions has been reported. Herein, we critically replicate and evaluate this new ferrate(VI) oxidation method. In addition, we test the use of potassium ferrate(VI) for the synthesis of graphene oxide under various experimental routes. The synthesized materials are analyzed by a number of analytical methods in order to confirm or disprove the possibility of synthesizing graphene oxide by the ferrate(VI) oxidation route. Our results confirm the unsuitability of using ferrate(VI) for the oxidation of graphite on graphene oxide because of its high instability in an acidic environment and low oxidation power in neutral and alkaline environments.     

C–C Bond Rupture in the Oxidation of Lower (C2–C6) Alcohols with Hydrogen Peroxide Mediated by Iron-Containing Compounds

C–C bond rupture upon the oxidation of alcohols in the Fe(ClO₄)₃+ H₂O₂system in aqueous acetonitrile at room temperature is found. The relative yield of the products of C–C bond rupture is 20–30% under standard conditions for C₂and C₃alcohols and decreases in the series C₂> C₃> C₄> C₆. The alkyl radical and carboxylic acid are the products of C–C bond rupture in alcohol oxidation. Cyclohexane is a competitive inhibiting agent for C–H bond oxidation in 1-propanol, and it does not affect the yield of the products of C–C bond rupture. When H₂O₂is replaced by tert-BuOOH, the fraction of the products of C–C bond rupture decreases by an order of magnitude. Our data suggest that a non-radical intermediate, likely Fe(III) hydroperoxo complex, is responsible for C–C bond rupture in alcohol under the reaction conditions.     

Phenol Oxidation by a Nickel(III)–Fluoride Complex: Exploring the Influence of the Proton Accepting Ligand in PCET Oxidation

In order to gain insight into the influence of the H⁺-accepting terminal ligand in high-valent oxidant mediated proton coupled electron transfer (PCET) reactions, the reactivity of a high valent nickel–fluoride complex [Ni^III(F)(L)] ( 2 , L=N,N’-(2,6-dimethylphenyl)-2,6-pyridinecarboxamidate) with substituted phenols was explored. Analysis of kinetic data from these reactions (Evans–Polanyi, Hammett, and Marcus plots, and KIE measurements) and the formed products show that 2 reacted with electron rich phenols through a hydrogen atom transfer (HAT, or concerted PCET) mechanism and with electron poor phenols through a stepwise proton transfer/electron transfer (PT/ET) reaction mechanism. The analogous complexes [Ni^III(Z)(L)] (Z=Cl, OCO₂H, O₂CCH₃, ONO₂) reacted with all phenols through a HAT mechanism. We explore the reason for a change in mechanism with the highly basic fluoride ligand in 2 . Complex 2 was also found to react one to two orders of magnitude faster than the corresponding analogous [Ni^III(Z)(L)] complexes. This was ascribed to a high bond dissociation free energy value associated with H−F (135 kcal mol⁻¹), which is postulated to be the product formed from PCET oxidation by 2 and is believed to be the driving force for the reaction. Our findings show that high-valent metal–fluoride complexes represent a class of highly reactive PCET oxidants.     

Selectivity Control of the Ligand Exchange at Carbon in α-Metallated Ylides as a Route to Ketenyl Anions**

α-Metallated ylides have recently been reported to undergo phosphine by CO exchange at the ylidic carbon atom to form isolable ketenyl anions. Systematic studies on the tosyl-substituted yldiides, R₃P=C(M)Ts (M=Li, Na, K), now reveal that carbonylation may lead to a competing metal salt (MTs) elimination. This side-reaction can be controlled by the choice of phosphine, metal cation, solvent and co-ligands, thus enabling the selective isolation of the ketenyl anion [Ts−CCO]M ( 2-M ). Complexation of 2-Na by crown ether or cryptand allowed structure elucidation of the first free ketenyl anion [Ts−CCO]⁻, which showed an almost linear Ts−C−C linkage indicative for a pronounced ynolate character. However, DFT studies support a high charge at the ketenyl carbon atom, which is reflected in the selective carbon-centered reactivity. Overall, the present study provides important information on the selectivity control of ketenyl anion formation which will be crucial for future applications.     

On the Reaction Mechanism of the Rhodium‐Catalyzed Arylation of Fullerene (C60) with Organoboron Compounds in the Presence of Water

Density functional theory (DFT) calculations were carried out to study the reaction mechanism of the Suzuki–Miyaura rhodium‐catalyzed hydroarylation of fullerene (C₆₀) by phenylboronic acid in the presence of water. As found experimentally, our results confirm that addition of the phenyl group and the hydrogen atom in C₆₀ occurs at the [6,6] bond. The rate‐determining step corresponds to the simultaneous transfer of a hydrogen atom from a water molecule to C₆₀ and the recovery of the active species. The use of 2‐phenyl‐1,3,2‐dioxaborinane and the 4,4,5,5‐tetramethyl‐2‐phenyl‐1,3,2,‐dioxaborolane instead of phenylboronic acid as organoborate agents does not lead to great modifications of the energy profile. The possible higher steric hindrance of 4,4,5,5‐tetramethyl‐2‐phenyl‐1,3,2,‐dioxaborolane should not inhibit its use in the hydroarylation of C₆₀. Overall, we show how organoboron species arylate C₆₀ in rhodium‐based catalysis assisted by water as a source of protons.     

Application of Enantiopure 1-(Aminoalkyl)naphthols and 2-(Aminoalkyl)phenols in the Enantioselective Addition of Organozinc to α,β-Unsaturated Carbonyl Compounds

Several enantiopure 1-(aminoalkyl)naphthols and a 2-(aminoalkyl)phenol were tested as ligands in the Nickel-catalyzed enantioselective addition of organozinc to chalcones.     

Selective Oxidation of Aryl Ketones to α-Diketones with 4-Aminoperoxybenzoic Acid Supported on Silica Gel in Presence of Air

Summary. 4-Aminoperoxybenzoic acid supported on silica gel in presence of air was found to be a selective and convenient oxidant for the oxidation of methylene groups in aryl ketones to convert them to -diketones.     

Development and Validation of a HPLC Method for the Determination of Five Bioactive Compounds in the “Xuebijing” Injection

A reversed phase high performance liquid chromatographic (RP-HPLC) method with ultraviolet (UV) detector was developed for simultaneously determining five bioactive components (i.e., hydroxysafflor yellow A: HSYA; paeoniflorin, ferulic acid, benzoic acid, and danshensu) in “Xuebijing” (XBJ) injection, a widely used traditional Chinese medicine (TCM) for treating sepsis and multiple organ dysfunction syndrome. A Zorbox SB C₁₈ column was used with 0.2% phosphoric acid (V/V)-acetonitrile as the mobile phase under the condition of gradient elution. The five components were analyzed by using a timed wavelength measure according to their maximum absorption wavelength. The intraday and interday precisions of the five investigated compounds were less than 1.17% and the average recoveries ranged from 97.3% to 103.2%. There were good linear correlations between the concentrations of the five components and their chromatographic peak areas (R² ≥ 0.9998), the proposed method was successfully applied to determine the five components in different batches of XBJ injection products, the results indicated that the proposed method is simple, stable, and accurate and could be readily utilized as a quality control method for manufacturing process of XBJ injection.