Multiple regioselective functionalizations of quinolines via magnesiations

A wide range of polyfunctionalized quinolines was prepared via chemo- and regioselective magnesiation reactions using appropriate Mg reagents, such as i-PrMgCl.LiCl, MesMgBr.LiCl, Mes2Mg.2LiBr, TMPMgCl.LiCl, and TMP2Mg.2LiCl. An application to the total synthesis of the biologically active compound talnetant was performed (six steps, 28%).     

立体选择性还原的硼试剂及其在手性药物合成中的应用

硼试剂在药物化学合成中广泛应用. 综述了可参与立体选择性还原反应的手性硼试剂、烷基硼试剂和硼氢化钠衍生物在手性药物合成中的应用, 并讨论这些试剂用于工业化生产的潜力.     

Tuning the potentials of "extra" electrons in colloidal n-type ZnO nanocrystals via Mg2+ substitution

Colloidal reduced ZnO nanocrystals are potent reductants for one-electron or multielectron redox chemistry, with reduction potentials tunable via the quantum confinement effect. Other methods for tuning the redox potentials of these unusual reagents are desired. Here, we describe synthesis and characterization of a series of colloidal Zn(1-x)Mg(x)O and Zn(0.98-x)Mg(x)Mn(0.02)O nanocrystals in which Mg(2+) substitution is used to tune the nanocrystal reduction potential. The effect of Mg(2+) doping on the band-edge potentials of ZnO was investigated using electronic absorption, photoluminescence, and magnetic circular dichroism spectroscopies. Mg(2+) incorporation widens the ZnO gap by raising the conduction-band potential and lowering the valence-band potential at a ratio of 0.68:0.32. Mg(2+) substitution is far more effective than Zn(2+) removal in raising the conduction-band potential and allows better reductants to be prepared from Zn(1-x)Mg(x)O nanocrystals than can be achieved via quantum confinement of ZnO nanocrystals. The increased conduction-band potentials of Zn(1-x)Mg(x)O nanocrystals compared to ZnO nanocrystals are confirmed by demonstration of spontaneous electron transfer from n-type Zn(1-x)Mg(x)O nanocrystals to smaller (more strongly quantum confined) ZnO nanocrystals.     

Chelation or Non-Chelation Control in Addition Reactions of Chiral α- and β- Alkoxy Carbonyl Compounds [New Synthetic Methods (44)]

The addition of C-nucleophiles such as Grignard reagents or enolates to chiral α- or β-alkoxy aldehydes or ketones creates a new center of chirality and is therefore diastereogenic. In order to control stereoselectivity, two strategies have been developed: (1) Use of Lewisacidic reagents which form intermediate chelates, these being attacked stereoselectively from the less hindered side (chelation control); (2) use of reagents incapable of chelation, stereoselective attack being governed by electronic and/or steric factors (non-chelation control). Generally, the two methods lead to the opposite sense of diastereoselectivity. It is possible to predict the outcome by careful choice of organometallic reagents containing elements such as Li, Mg, B, Si, Sn, Cu, Zn, or Ti. For corrigendum see DOI: 10.1002/anie.198407461     

Transformation of aromatic bromides into aromatic nitriles via formations of grignard reagents and their DMF adducts

Various aromatic bromides were efficiently transformed into the corresponding aromatic nitriles in good yields via the formations of Grignard reagents and subsequently N,N-dimethyl formamide (DMF) adducts, followed by treatment with molecular iodine (I₂) in aq NH₃ at room temperature. The present reaction is an easy and practical method for the preparation of aromatic nitriles from aromatic bromides with less toxic reagents, such as Mg, DMF, I₂, and aq NH₃.     

Reductive Cross‐Coupling Reactions between Two Electrophiles

Reductive cross‐electrophile coupling reactions have recently been developed to a versatile and sustainable synthetic tool for selective C?C bond formation. The employment of cheap and abundant electrophiles avoids the pre‐formation and handling of organometallic reagents. In situ reductive coupling is effected in the presence of a transition‐metal catalyst (Ni, Co, Pd, Fe) and a suitable metallic reductant (Mn, Zn, Mg). This Concept article assesses the current state of the art and summarizes recent protocols with various combinations of alkyl, alkenyl, allyl, and aryl reagents and highlights key mechanistic studies.     

甲基百里香酚蓝三元络合物光度法测定空气中的微量镉

本文研究了用镉-甲基百里香酚蓝-溴化十六烷基三甲基铵三元络合物光度测定镉的反应条件和络合物组成。本法具有灵敏度高,选择性好等优点。其最大特点是显色较迅速,颜色稳定。在文中还提出了用氟化铵,邻菲啰啉作为镍、钴、镁等离子的掩蔽剂,制定了不经分离快速测定空气中微量镉的新方法。     

Recent advance in heterocyclic organozinc and organomanganese compounds; direct synthetic routes and application in organic synthesis

A practical synthetic route for the preparation of 2-pyridyl and 3-pyridyl derivatives has been accomplished by utilizing a simple coupling reaction of stable 2-pyridylzinc bromides and 3-pyridylzinc bromides. The organozincs used in this study were easily prepared via the direct insertion of active zinc into the corresponding bromopyridines. The subsequent coupling reactions with a variety of different electrophiles have afforded the corresponding coupling products. Using highly active manganese, a variety of Grignard-type organomanganese reagents have been obtained. The subsequent coupling reactions of the resulting organomanganese reagents with several electrophiles have also been accomplished under mild conditions.     

Novel functionalized trisubstituted allylboronates via Hosomi-Miyaura borylation of functionalized allyl acetates

[reaction: see text] A series of novel functionalized achiral and chiral allylboronates have been synthesized via the nucleophilic addition of boronates on allyl acetates derived via vinylalumination or Baylis-Hillman reaction of aldehydes. These reagents, upon allylboration with aldehydes, furnish beta-substituted-alpha-methylene-gamma-butyrolactones stereoselectively.     

Iron-catalyzed unexpected easy access to stereodefined trimethylsilyl vinyl ketenes

Stereodefined trimethylsilyl vinyl ketenes with polysubstitution have been synthesized highly regio- and stereoselectively via an iron-catalyzed reaction of 2-trimethylsilyl-2,3-allenoates with Grignard reagents in good to excellent yields. The reaction was believed to proceed via a conjugate addition and elimination mechanism. Applications of the products for the synthesis of stereodefined α-silyl-β,γ-unsaturated enones, a stereodefined triene, and polysubstituted phenols have been carefully demonstrated.     

Generation of reactive low-valent titanium species using metal--arenes as efficient organic reductants for TiCl(3): applications to organic synthesis

A comprehensive study on the use of metal-arene systems as organic reductants for TiCl(3) has resulted in an efficient method for the generation of highly reactive low-valent titanium (LVT) reagents. The activated titanium species could be prepared by refluxing a mixture of substoichiometric amounts of arenes, TiCl(3), and Li/Mg in THF or DME. Among the LVT reagents screened, TiCl(3)--Li--naphthalene--THF (reagent I) was the best for coupling of carbonyls to olefins. The reagent could carry out the McMurry olefination of both aromatic and aliphatic substrates at a lower temperature and in a much reduced time as compared to the conventional procedures. Subtle changes in the method of preparation of the LVT reagents influenced the stereoisomeric ratio of the olefins. The reagent was also useful for the synthesis of O- and N- heterocycles and vicinal diamines via intramolecular carbonyl coupling and reductive duplication of imines, respectively.     

Boronates allyliques,alleniques et propargyliques: Preparations et proprietes

An easy synthesis of linear cyclic 2-unsaturated boronates via organometallic reagents has been achieved. The final structure of the carbon framework is related to the tetracoordinated intermediate. Intermolecular rearrangement, disproportionation and reactions with carbonyl compounds have been studied.     

Oxidation-Reduction Condensation a New Method for Peptide Synthesis

Organic trivalent phosphorous compounds such as trialkyl phosphites and trialkyl or triarylphosphines are well known to be powerful deoxygenation reagents and have been used in various reduction reactions. But, it is rather a new aspect to make use of their property of deoxygenation for the gsneration of active acyl groups. Since the discovery of the rezcticn of mercuric acetate with trivalent phosphorous coqounds to yield acetic anhydride, our attention has been fccused on the generation of acyl groups and several novel reactions have been found which are applicable to the preparation of acid anhydride and peptide linkages. In considering these reactions described herein, it is necessary to choose appropriate oxidation reagents together with reducing reagents (trivalent phosphcrous compounds) because these dehydration reactions essentially proceed via an oxiaation reduction process as depicted in the following scheme.     

Acceleration of the corrosion reaction of magnesium by Fenton reagents

Abstract

Magnesium alloys have attracted increased attention for a variety of applications, chief among which are alternative energy and medical implants. The use of biodegradable implants in the complex system of the human body, in which myriad reactions occur, must consider the potential effects of the body’s natural chemical reactions on implant corrosion rates. The aim of this study was to elucidate the synergistic effects of pure Mg and Mg alloys on the Mg corrosion reaction with reagents that participate in the Fenton reaction. We corroborated our results with six different measurement methods (hydrogen evolution rate [HER], gas chromatography [GC], potentiodynamic polarization, inductively coupled plasma [ICP] spectrometry, Auger electron spectroscopy [AES], and scanning electron microscope [SEM]). The results point out that the corrosion and hydrogen evaluation rates of Mg were elevated by the addition of Fenton reagents, divalent iron and hydrogen peroxide, to a saline solution. In the context of Mg-based alloy medical implant development and use, this observation is significant.     

Complete functionalisation of small and large diameter bromopolystyrene beads; applications for solid-supported reagents, scavengers and diversity-oriented synthesis

Bromopolystyrene beads with diameters of up to 600 microm have been derivatized completely, via bromine-magnesium exchange and interception with electrophiles, to yield high quality solid-supported reagents, scavengers and solid supports for use in diversity-oriented synthesis.     

Iron(II) complexes with functionalized amine-pyrazolyl tripodal ligands in the cross-coupling of aryl Grignard with alkyl halides

Structurally distinctive Fe(II) complexes with furan, thiophene and pyridine functionalized amine-pyrazolyl tripodal hybrid ligands have been synthesized and crystallographically characterized. The tether substituent at the central amine plays an active role in determining the coordination mode of the ligand and the metal geometry. All complexes are catalytically active towards cross-coupling of aryl Grignard reagents with primary and secondary alkyl halides with β-hydrogen under ambient conditions. ESI-MS spectra analysis revealed the ligand-stabilised Fe(II) and Mg(II) species.     

One-step preparation of functionalized (E)-vinylsilanes from aldehydes

Functionalized (E)-vinylsilanes have been prepared in one step from a wide range of aldehydes, via a chromium(II)-mediated olefination with novel dihalomethylsilane reagents, in moderate to excellent yields and with excellent stereoselectivity.     

Novel and Efficient Cyclization Procedure for the Synthesis of 2,5-Disubstituted-1,3,4-thiadiazoles Without Using Any Ring-Closing Reagents

A novel method for the synthesis of 2,5-disubstituted-1,3,4-thiadiazoles via direct ring closure of 1,6-disubstituted-2,5-dithioureas in dimethylformanide without using any ring-closing reagents has been accidentally discovered. Repeated and extended experiments confirmed that this is a very simple and efficient way to synthesize these kinds of fine chemicals. A series of novel 2,5-disubstituted-1,3,4-thiadiazoles have been synthesized via this method in good yields.     

Polyfunctional Lithium,Magnesium, and Zinc Alkenyl Reagents as Building Blocks for the Synthesis of Complex Heterocycles

New conjunctive β‐silylated organometallic reagents of Li, Mg, and Zn have been prepared and used for an expeditive construction of various polyfunctionalized 5‐, 6‐, and 7‐membered heterocycles, such as furans, pyrroles, quinolines, benzo[b]thieno‐[2,3‐b]pyridine, naphthyridines, fused pyrazoles, and 2,3‐dihydro‐benzo[c]azepines. The latent silyl group has been converted into various carbon–carbon bonds in most heterocycle types.     

Microwave-Assisted Carbonyl–Carbonyl Coupling Route for the Preparation of a Useful Intermediate in the Synthesis of Carbapenems

Microwave-assisted organic synthesis has been used for the cyclization of a monocyclic oxoamide to the corresponding bicyclic derivative via a Wittig-type coupling by means of phosphite reagents. The parameters influencing the reaction yields under microwave (dielectric heating) and classical conditions (convective heating) have been evaluated.