Iron‐Catalyzed C?H Bond Activation for the ortho‐Arylation of Aryl Pyridines and Imines with Grignard Reagents

Direct arylation of the ortho‐C? H bond of an aryl pyridine or an aryl imine with an aryl Grignard reagent has been achieved by using an iron‐diamine catalyst and a dichloroalkane as an oxidant in a short reaction time (e.g., 5 min) under mild conditions (0 °C). The use of an aromatic co‐solvent, such as chlorobenzene and benzene, and slow addition of the Grignard reagent are essential for the high efficiency of the reaction. The present arylation reaction has distinct merits over the previously developed reaction that used an arylzinc reagent, such as its reaction rate and atom economy. Selective C? H bond activation occurs in the presence of a leaving group, such as a tosyloxy, chloro, and bromo group. Studies on a stoichiometric reaction and kinetic isotope effects shed light on the reaction intermediate and the C? H bond‐activation step.     

Reaction pathways of the Simmons-Smith reaction

The cyclopropanation reaction of an alkene with a metal carbenoid has been studied by means of the B3LYP hybrid density functional method. The cyclopropanation of ethylene with a lithium carbenoid or a zinc carbenoid [Simmons-Smith (SS) reagent] goes through two competing pathways, methylene transfer and carbometalation. Both processes are fast for the lithium carbenoid, while, for the zinc carbenoid, only the former is fast enough to be experimentally feasible. The reaction of an SS reagent (ClZnCH(2)Cl) with ethylene and an allyl alcohol in the presence of ZnCl(2) was also studied. The allyl alcohol reaction was modeled with an SS reagent/alkoxide complex (ClCH(2)ZnOCH(2)CH=CH(2)) formed from the SS reagent and allyl alcohol. Two modes of acceleration were found. The first involves the well-accepted mechanism of 1,2-chlorine migration, and the second involves a five-centered bond alternation. The latter was found to be more facile than the former and to operate equally well both with ethylene and with aggregates of SS reagent/alkoxide complexes. Calculations on the SS reaction with 2-cyclohexen-1-ol offer a reasonable model for the hydroxy-directed diastereoselective SS reaction, which has been used for a long time in organic synthesis.     

A Catalyst‐Free Amination of Functional Organolithium Reagents by Flow Chemistry

Reported is the electrophilic amination of functional organolithium intermediates with well‐designed aminating reagents under mild reaction conditions using flow microreactors. The aminating reagents were optimized to achieve efficient C?N bond formation without using any catalyst. The electrophilic amination reactions of functionalized aryllithiums were successfully conducted under mild reaction conditions, within 1 minute, by using flow microreactors. The aminating reagent was also prepared by the flow method. Based on stopped‐flow NMR analysis, the reaction time for the preparation of the aminating reagent was quickly optimized without the necessity of work‐up. Integrated one‐flow synthesis consisting of the generation of an aryllithium, the preparation of an aminating reagent, and their combined reaction was successfully achieved to give the desired amine within 5 minutes of total reaction time.     

Quantum Wave Packet Studies on F ＋ HBr Reaction

IntroductionA series of reactions of fluorine atoms with hydro-gen halidesF HCl HF Cl (1)(ΔH—00=-137·10 kJ/mol)F HBr HF Br (2)(ΔH—00=-202·73 kJ/mol)F HI HF I (3)(ΔH—00= -270·45 kJ/mol)belongs to the prototypical heavy-light-heavy reactionsa     

The different roles of reagent vibrational excitation for endothermic and exothermic reactions

The surprisal analysis of trajectory generated rate constants of three endoergic reactions is employed to compare the actual effect of reagent vibrational excitation to that expected on purely energetic grounds. It is shown that the enhancement of the reaction rate is not a function of the potential energy surface alone. Rather, reagent vibrational energy has an opposite effect (as compared to the statistical limit) in the endothermic and exothermic regimes of a given endoergic reaction.     

The role of neat substrates in phase-vanishing and tandem phase-vanishing reactions

Phase-vanishing reactions are triphasic reactions, which involve a reagent, a liquid perfluoroalkane as a phase screen and a substrate. Aromatization, isomerization and halogenation of neat substrates under phase-vanishing conditions gave the expected products in good to excellent yields. In tandem single-phase-phase-vanishing reaction, two reactants, placed in the top phase, afforded the intermediate, which in a subsequent phase-vanishing reaction reacted with the reagent from the bottom phase to give the final product. The reaction worked well under solvent-free conditions on liquid substrates and intermediates. With solids, results were better if an additional solvent was employed.     

低价钛诱导的芳香邻二酮及α-羟基酮的还原偶联反应

Treatment of aromatic 1 , 2-diketones or aromatic a-hydroxy ketones with an activated low-valent titanium reagent, prepared by reduction of TiCl3·1/3AlCl3 with a Zn-Cu reagent, gave an intermolecular coupling reaction leading to the (Z)-1, 2.3.4-tetraaryl-2-butenes. Apossible coupling reaction process was proposed for the aromatic a-hydroxy ketones.     

(PhCH2PPh3)+Br3 −: A Versatile Reagent for the Chemoselective Oxidation of Sulfides to Sulfoxides

Benzyltriphenylphosphonium tribromide (BTPTB), as a stable solid reagent, is easily prepared by the reaction of benzyltriphenylphosphonium bromide with Br₂. This reagent can be used as an efficient reagent for the chemoselective oxidation of dialkyl and aryl-alkyl sulfides to their corresponding sulfoxides in the presence of diaryl sulfides and primary alcohols. All reactions were performed in a refluxing mixture of methanol and water in very short reaction times.     

Grafting onto chitosan. I. Graft copolymerization of methyl methacrylate onto chitosan with Fenton's reagent (Fe2+−H2O2) as a redox initiator

Poly(methyl methacrylate) has been grafted onto chitosan by using Fenton's reagent as a redox initiator in an aqueous medium. Initiation by Fenton's reagent was carried out in the presence of atmospheric oxygen. The percentages of grafting, efficiency, and homopolymer were found to depend on chitosan (RchitOH), ferrous ammonium sulfate (FAS), hydrogen peroxide, monomer (MMA) concentrations, reaction temperature, and reaction time.     

Oxidative transformation of aryls using molybdenum pentachloride

Molybdenum pentachloride combines a strong Lewis acid character with an unusually high oxidation potential creating a powerful reagent for oxidative transformations. Since the oxidative coupling reaction of aryls is induced at an extraordinarily high reaction rate, a variety of labile groups, e.g. iodo, tert-alkyl, etc., are tolerated on the aromatic core. Furthermore, the co-formed molybdenum salts can either be exploited for template effects to obtain uncommon geometries in a preferred manner, or redox-play starts after aqueous workup. Therefore MoCl(5) represents a unique and easily available reagent.     

An advantageous reagent for the removal of elemental sulfur from environmental samples

Polymeric triphenylphosphine is introduced as an efficient reagent for the removal of elemental sulfur from environmental samples. It is compared with several traditional reagents, particularly heavy metals. For all reagents, ultrasonication was much preferable to stirring or shaking the reaction solution. Advantages of the new reagent include quantitative reaction with sulfur, few side-reactions with analytes, ease of handling and non-hazardous products. The used reagent can be regenerated and reused.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthdayPresented in part at Anakon '93 in Baden-Baden, May 1993     

Spectrophotometric study of bromide interference in a cholesterol reaction

A spectrophotometric study of the interference of bromide in the ferric chloride reaction for cholesterol has been described. The interference has been shown to be primarily an enhancement of the color reaction and secondarily an additive color owing to a change in the spectrum of the reagent blank. Tested methods of eliminating the interference included removal of bromide by ion exchange, metathetical exchange using AgIO₃, addition of bromide to a reaction plateau and a change in the solvent character of the reaction medium. It was determined that the use of an ion-exchange resin and the substitution of ethanol for acetic acid along with a modified iron reagent were the simplest choices for eliminating bromide interference in this determination. Iodate was shown to depress color formation and it appears to be a detrimental solution to the problem. Further work on the mechanism of the iodate interference is presently in progress.     

A flow injection analysis technique for the determination of chloride using reflectance detection

A flow injection (FI) determination for chloride has been developed using the light reflectance of the precipitate formed by the reaction of chloride with silver(I) as the method of detection rather than turbidimetry, as in the previous FI method using this reaction. The dynamic range of the analysis is increased to 0-10 mM chloride with a 10 mM silver(I) reagent and to 0-50 mM chloride with a 50 mM silver(I) reagent by using this mode of detection. The ability to select the injected reagent from an option of two concentrations via the control program is incorporated into the FI system, enhancing the versatility of the analysis. The dynamic range is further extended to 100 mM chloride by measuring the signal levels at the trailing portion of the response curve. The consumption of reagent is kept to a minimum by merging injected zones of sample and reagent instead of using a constant reagent stream.     

Characterization of a titanium(IV)–porphyrin complex as a highly sensitive and selective reagent for the determination of hydrogen peroxide: a computational chemistry approach and a critical review

The Ti–TPyP reagent, i.e. an acidic aqueous solution of the oxo[5,10,15,20-tetra(4-pyridyl)porphyrinato] titanium(IV) complex, TiO(tpyp), was developed as a highly sensitive and selective spectrophotometric reagent for determination of traces of hydrogen peroxide. Using this reagent, determination of hydrogen peroxide was performed by flow-injection analysis with a detection limit of 0.5 pmol per test. The method was actually applied to determination of several constituents of foods, human blood, and urine mediated by appropriate oxidase enzymes. The reaction specificity of the TiO(tpyp) complex for hydrogen peroxide was clarified from the viewpoint of the reaction mechanisms and molecular orbitals based on ab initio calculations. The results provided a well-grounded argument for determination of hydrogen peroxide using the Ti–TPyP reagent experimentally. This review deals with characterization of the high sensitivity and reaction specificity of the Ti–TPyP reagent for determination of hydrogen peroxide, to prove its reliability in analytical applications. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis of tertiary and quaternary stereogenic centers: a diastereoselective tandem reaction sequence combining Mukaiyama and free radical-based allylation

Reported herein is a strategy employing a Mukaiyama reaction in tandem with a free radical-based allyl transfer reaction for the elaboration of functionalized tertiary and quaternary centers. The appropriate choice of alcohol-protecting group on the starting alpha-methyl-beta-hydroxyaldehyde and the nature of the Lewis acid used in the Mukaiyama reaction provided access to 3,4-anti and 3,4-syn aldolization products, precursors of the free-radical allylation reaction. After migration or exchange of the Lewis acid, the allyl transfer reaction with allyltributylstannane is then performed by taking advantage of the endocyclic effect, leading to the 2,3-anti relative stereochemistry. Importantly, (13)C NMR studies of the chelated intermediates are also reported and provide additional support for the endocyclic effect. In some cases, the remarkable reactivity of the aluminum-based Lewis acids allowed the use of allyltrimethylsilane, an interesting reagent from an ecological standpoint. The isolation of a key intermediate is also indicative of an atom transfer mechanism when the silicon-based reagent is employed.     

Dichlorodimethylhydantoin-KF as an efficient reagent for one pot synthesis of dialkylfluorophosphates from dialkylphosphites

Organic-inorganic hybrid reagent dichlorodimethylhydantoin-KF (DCDMH-KF) mixture was explored as an efficient reagent for the direct conversion of dialkylphosphites to their corresponding dialkylfluorophosphates at room temperature and in shorter reaction times through a facile electrophilic-nucleophilic metathesis.     

Reaction specificity of a titanium(IV)-porphyrin complex to hydrogen peroxide in view of an Ab initio study.

A Ti-TPyP reagent, i.e. an acidic aqueous solution of oxo[5,10,15,20-tetra(4-pyridyl)porphyrinato]titanium(IV) complex, TiO(tpyp), was previously developed as a highly sensitive and specific reagent for determining hydrogen peroxide. In the present work, the reaction specificity of the TiO(tpyp) complex to hydrogen peroxide was clarified based on ab initio calculations. The results provide a well-grounded argument for determining hydrogen peroxide using the Ti-TPyP reagent experimentally.     

Development of an impregnated reagent and automation of solid-phase analytical derivatization for carbonyls: proof of principle

This study undertakes reduction of scale and automation of a solid-phase analytical derivatization of carbonyls with 2,4-dinitrophenylhyrazine on a styrene-divinylbenzene resin (XAD-2). Three processes are tested. In the batch process, an aqueous phase consisting of 50 microL of sample and 150 microL of reagent solution is contacted with 6 mg XAD-2 by shaking. An impregnated reagent consisting of 2,4-dinitrophenylhydrazine hydrochloride (DNPH) deposited on XAD-2 enables two additional processes. In-vial derivatization with an impregnated reagent requires shaking 50 microL of sample with 6 mg of the impregnated reagent and reduced the reaction time from 10 to 5 min. The third process involves packing impregnated reagent a mini-column and flowing 50 microL of sample through under positive pressure supplied by a Harvard Pump. This reduces sample preparation time to 1 min. Studies are conducted with worst-case model analytes: butanone, 2-pentanone, and malonyldialdehyde. The carbonyl of the two ketones is hindered, and, thus, these two compounds react very slowly with DNPH in aqueous solution. Malonyldialdehyde is highly water soluble, and it does not react in aqueous phase but also would not sorb onto XAD-2 for reaction. Nevertheless, derivatization/extraction of all model compounds any of the three procedures result in reproducible and high yields.     

Selective cleavage of allyl and propargyl ethers to alcohols catalyzed by Ti(O-i-Pr)4/MXn/Mg

[reaction: see text] Allyl and propargyl ethers were effectively deallylated or depropargylated to the parent alcohols via a C-O bond cleavage catalyzed by a low-valent titanium reagent (LVT), Ti(O-i-Pr)4/TMSCl/Mg or Ti(O-i-Pr)4/MgBr2/Mg, under mild reaction conditions. Differentiation between the allyl and propargyl ethers was achieved by the reaction in the presence of AcOEt as an additive. The reagent also catalyzed intra- and intermolecular cyclotrimerization reactions of alkynes to substituted benzenes.