Theoretical study of Lewis acid activation models for hypervalent fluoroiodane reagent: The generality of “F-coordination” activation model

The bench-stable cyclic hypervalent fluoroiodane reagent (1) is receiving increasing attention in fluorine chemistry because of its completely new reactivity. Fluorination mediated by reagent 1 generally requires activation by an exogenous Lewis acid. A more complete understanding of the Lewis acid activation model is thus paramount for the development of new strategies involving this reagent. Density functional theory (DFT) calculations herein demonstrate the generality of the “F-coordination” activation mechanism for reagent 1 that we recently showed to be favored over the commonly accepted “O-coordination” activation mechanism.     

A general method for one-step synthesis of monofluoroiodane(III) reagents using silver difluoride

Herein we report a new general method for one-step synthesis of four kinds of fluoroiodane(III) reagents by treating the corresponding aryl iodides with silver difluoride (AgF₂). This is the first method applicable for the synthesis of all four fluoroiodane(III) reagents including p-iodotoluene difluoride (1), fluoro-benziodoxole (2), fluoro-benziodoxolone (3), and fluoro-N-acetylbenziodazole (4). AgF₂ was firstly employed in the direct oxidative fluorination of iodobenzene and thus has shown its outstanding oxidation and fluorine-transfer ability. The use of AgF₂ has improved the synthesis of fluoroiodane(III) reagents by shortening the reaction steps, avoiding the use of hazardous reagents, and simplifying the experimental operations. It was worth noting that we have developed the first one-step direct synthetic method for 3, while 3 can only be synthesized through Cl→F ligand exchange reaction previously.     

Mild Silver‐Mediated Geminal Difluorination of Styrenes Using an Air‐ and Moisture‐Stable Fluoroiodane Reagent

An air‐ and moisture‐stable fluoroiodane in the presence of AgBF₄ is suitable for selective geminal difluorination of styrenes under mild reaction conditions. One of the C? F bonds is formed by transfer of electrophilic fluorine from the hypervalent iodine reagent, while the other one arises from the tetrafluoroborate counterion of silver. Deuterium‐isotope‐labelling experiments and rearrangement of methyl styrene substrates suggest that the reaction proceeds through a phenonium ion intermediate.     

A Safe,Simple and Rapid Synthesis of t-Butyl Chromate

Di-t-butyl chromate -(t-BuO)₂CrO₂, DTBC- has proven to be a potent and versatile oxidizing reagent, suitable for the direct introduction of a carbonyl group in an allylic position¹. The compound was prepared for the first time by Wienhaus² but Oppenauer³ introduced it as a new oxidizing reagent. DTBC is a crystalline compound with a melting point of 0°C^3,4 and is never used as such but always in a solution of a non polar solvent.     

Simple synthesis of mixed cellulose acylate phosphonates applying n-propyl phosphonic acid anhydride

Cellulose mixed esters containing alkylphosphonate and carboxylate groups were prepared homogeneously by a new one-pot method using n-propyl phosphonic acid anhydride (T3P^?) in LiCl/N-methyl-2-pyrrolidone (NMP). n-Propyl phosphonic acid anhydride acts as both an activating agent for carboxylic acids and phosphonation reagent. Cellulose mixed esters with DS_acyl ranging from 1.4 to 1.8, and DS_phos up to 0.7 could be prepared. The structure of the cellulose mixed esters was elucidated by FTIR- and NMR spectroscopy, as well as by GPC and solubility tests.     

Synthesis,Characterization, X‐Ray Structural Analysis,and Iodination Ability of Benzyl(triphenyl)phosphonium Dichloroiodate

Benzyl(triphenyl)phosphonium dichloroiodate (BTPPICl₂), BnPh₃P⁺(ICl₂)^?, is easily synthesized in a nearly quantitative yield by the addition of BnPh₃P⁺Cl^? to a CH₂Cl₂ solution of iodine monochloride (ICl). BnPh₃P⁺Cl^? can be prepared by the reaction of Ph₃P and BnCl. The compound was characterized by physicochemical and spectroscopic methods (elemental analysis, FT‐IR, and ¹H‐NMR). The use of phosphonium counterion improves the quality of the BTPPICl₂ crystals. BTPPICl₂ crystallizes in the monoclinic system, and its crystal and molecular structure has been determined at 100(1) K by X‐ray diffraction. The structure was solved by the direct method and had refined R value of 0.0637 for 699 reflections (I>2σ(I)), space group P21/n with a=12.4700(3), b=13.2196(3), c=14.4580(3) Å, β=102.6340(10)°, V=2325.67(9) ų, and Z=4. The I‐atom is coordinated by two Cl‐atoms as ligands in a linear geometry. This compound is a versatile reagent for the efficient and selective iodination of organic substrates, in particular of aromatic phenols to the corresponding iodo compounds, under mild conditions. To assess the generality of method, a wide variety of phenols with electron‐donating and electron‐withdrawing substituents were studied. BTPPICl₂ is a mild iodination reagent, which offers a new avenue for an expeditious iodination of phenols. The inexpensive, relatively non‐toxic reagent, and mild conditions are the positive features of the procedure and reagent.     

Asymmetric ring opening of meso-epoxides with B-halobis(2-isocaranyl)boranes 2-dIcr2BX

Hydroboration of commercially available (+)-2-carene (96% ee) with either BH₂Cl·SMe₂ or BCl₃/Me₃SiH, provides chemically pure B-chlorobis(2-isocaranyl)borane (2-^dIcr₂BCl) whereas B-bromobis(2-isocaranyl)borane (2-^dIcr₂BBr) could only be prepared by Matteson’s BBr₃/Me₃SiH procedure in high chemical yield and purity. The enantiomeric excess achieved with 2-^dIcr₂BCl (78%), was significantly higher than those realized with the previously explored reagent, ^dIpc₂BCl (41%), especially for meso-cyclohexene oxide. The new reagent, 2-^dIcr₂BBr also showed considerable improvements in enantiomeric excesses, in the cases of meso-cyclopentene oxide (67%) and meso-cis-2,3-butene oxide (78%) than those achieved with the previously reported reagent, ^dIpc₂BBr (57% and 61%, respectively).     

Reactions of a phosphavinyl Grignard reagent with main group mono-halide compounds

The reactions of a phosphavinyl Grignard reagent, [CyPC(Bu^t)MgCl(OEt₂)] Cy=cyclohexyl, with a variety of main group 13, 14 and 16 mono-halide compounds have been investigated. When the Grignard reagent is reacted with bromocatecholborane the terminal phosphavinyl complex, [(C₆H₄O₂)B{C(Bu^t)PCy}], is formed. Related terminal phosphavinyl tin and gallium complexes, [R₃Sn{C(Bu^t)PCy}], R=Me or Buⁿ and [IGa{C(Bu^t)PCy}₂], have been prepared by similar routes. The reaction of the Grignard reagent with PhSeCl has afforded a new λ⁵,λ⁵-diphosphete, [{(Bu^t)CP(Cy)(SePh)}₂], the mechanism of formation of which is discussed. The preparation of a phosphavinyl selenium compound, [(C₈H₄O₂N)PC(Bu^t)(SePh)], is also described. All compounds have been spectroscopically characterised and several have been crystallographically authenticated.     

Eco-Friendly Methodology for the Formation of Aromatic Carbon–Heteroatom Bonds by Using Green Ionic Liquids

A new sustainable method is reported for the formation of aromatic carbon–heteroatom bonds under solvent-free and mild conditions (no co-oxidant, no strong acid and no toxic reagents) by using a new type of green ionic liquid. The bromination of methoxy arenes was chosen as a model reaction. The reaction methodology is based on only using natural sodium bromine, which is transformed into an electrophilic brominating reagent within an ionic liquid, easily prepared from the melted salt FeCl₃ hexahydrate. Bromination reactions with this in-situ-generated reagent gave good yields and excellent regioselectivity under simple and environmentally friendly conditions. To understand the unusual bromine polarity reversal of sodium bromine without any strong oxidant, the molecular structure of the reaction medium was characterised by Raman and direct infusion electrospray ionisation mass spectroscopy (ESI-MS). An extensive computational investigation using density functional theory methods was performed to describe a mechanism that suggests indirect oxidation of Br⁻ through new iron adducts. The versatility of the methodology was successively applied to nitration and thiocyanation of methoxy arenes using KNO₃ and KSCN in melted hexahydrated FeCl₃.     

Large-scale synthesis of high purity “Phos reagent” useful for oligonucleotide therapeutics

A large-scale, cost-effective, and environmentally clean synthesis of high purity 2-cyanoethyl-N,N,N′,N′-tetraisopropylphosphorodiamidite (Phos reagent) has been accomplished on a commercial scale. Treatment of PCl₃ with diisopropylamine followed by 3-hydroxylpropionitrile furnished the Phos reagent in excellent yield. The ³¹P NMR of the Phos reagent prepared at large-scale show consistent purities >99% when several key factors are controlled. These controlling factors include sourcing high purity key raw materials, identification and elimination of critical impurities, stability and storage of Phos reagent.     

Preparation and properties of dimethyl phosphonomethyl methylsiloxane dimethylsiloxane copolymers

Dimethyl phosphonomethylheptamethylcyclotetrasiloxane (II) and 1, 3-bis(dimethyl phosphonomethyl)tetramethyldisiloxane (III) have been prepared by Arbuzov reaction of trimethyl phosphite with bromomethylheptamethylcyclotetrasiloxane (I) and 1, 3-bis(bromomethyl)tetramethyldisiloxane, respectively. Dimethyl phosphonomethylmethylsiloxane dimethylsiloxane copolymers have been prepared by acid-catalyzed ring-opening polymerization of II with hexamethyldisiloxane (MM) as an end-capping reagent and by reaction of II with III as an end-capping reagent. Dimethylsiloxane polymers with dimethyl phosphonomethyldimethylsiloxy end groups have been prepared by acid-catalyzed polymerization of octamethylcyclotetrasiloxane (D₄) and III. Under these conditions hydrolysis of the dimethyl phosphonate ester groups was a problem. On the other hand Arbuzov reaction of trimethyl phosphite with bromomethylmethylsiloxane dimethylsiloxane copolymer gave a dimethyl phosphonomethylmethylsiloxane dimethylsiloxane copolymer with uniform properties. These polymers have been characterized by ¹H-, ¹³C-, ²⁹Si-, and ³¹P-NMR spectroscopy. Their molecular weight distributions have been determined by gel permeation chromatography (GPC) and their thermal stability measured by TGA.     

Cis‐1‐phosphabicyclo[3.3.0]octan

A new approach to 1‐phosphabicyclo[3.3.0]octane compounds starts from the reaction of 4‐chloro‐hepta‐1.6‐diene with Mg in THF. No Grignard rearrangement is observed. The Grignard reagent is converted into 1‐allyl‐3‐butenylphosphonous dichloride followed by reduction with LiAlH₄. Cis‐1‐phosphabicyclo[3.3.0]octane has been prepared by radical‐initiated cyclization of 1‐allyl‐3‐butenylphosphane. The bicyclic phosphane is characterized by analytical data as well as ³¹P and ¹³C NMR measurements and the reactionswith NO, S₈, KSeCN, CH₃I, Ni(CO)₄ and HSO₃F, respectively.     

2 D Manganese Vanadate Nanoflakes as High‐Performance Anode for Lithium‐Ion Batteries

Nanometer‐sized flakes of MnV₂O₆ were synthesized by a hydrothermal method. No surfactant, expensive metal salt, or alkali reagent was used. These MnV₂O₆ nanoflakes present a high discharge capacity of 768 mA h g^?1 at 200 mA g^?1, good rate capacity, and excellent cycling stability. Further investigation demonstrates that the nanoflake structure and the specific crystal structure make the prepared MnV₂O₆ a suitable material for lithium‐ion batteries.     

Direct electrochemistry and electrocatalysis of hemoglobin on a gold ion implantation-modified indium tin oxide electrode

In this paper, a gold nanoparticle-modified indium tin oxide electrode (Au/ITO) was prepared without the use of any cross-linker or stabilizer reagent. The prepared Au/ITO was used as a new platform to achieve the direct electron transfer between Hb and the modified electrode. The proposed electrode exhibited a pair of well-defined redox peaks with a formal potential of ?0.073 V (vs. Ag/AgCl). The immobilized Hb showed excellent electrocatalytic activity toward H₂O₂ and the electrocatalytic current values were linear with the increasing concentration of H₂O₂ ranging from 1.0?×?10^?6?M to 7.0?×?10^?4?M. The detection limit was 2.0?×?10^?7?M (S/N?=?3) and the Michaelis–Menten constant was calculated to be 0.2 mM. The proposed electrode also showed high selectivity, long-term stability, and good reproducibility.     

高分子保护沉淀法制备超细纳米氧化镁

纳米氧化镁具有不同于本体材料的光、电、磁、化学特性,特别是超细纳米氧化镁由于其颗粒直径小、比表面积大,具有高纯度、高硬度和高熔点,高的反应活性,强吸附性,良好的低温烧结性,高电阻率等优良性质,可用于高绝缘材料,高质量的陶瓷材料,高性能阻燃纤维,环境保护的吸附剂、负载型甲醇和低碳醇合成的催化剂载体等领域,是一种有广泛应用价值的新型无机材料[1￣5]。已见报道的纳米氧化镁的制备方法有电子束蒸发法[6]、化学气相沉积法[7]、金属醇盐水解法,化学沉淀法[8,9],固相法[10],燃烧法[11],溶胶-凝胶法[12,13]等,然而由于氧化镁容易发生…     

Intermolecular Amination of Unactivated C(sp3)−H Bonds with Cyclic Alkylamines: Formation of C(sp3)−N Bonds through Copper/Oxygen‐Mediated C(sp3)−H/N−H Activation

The first example of intermolecular amination of unactivated C(sp³)?H bonds by cyclic alkylamines mediated by Cu(OAc)₂/O₂ is reported. This method avoids the use of benzoyloxyamines as the aminating reagent, which are normally prepared from alkylamines in extra steps. A variety of unnatural β^{2, 2}‐amino acid analogues are synthesized by this simple and efficient procedure. This approach offers a solution to the previous unmet challenge of C(sp³)?H/N?H activation for the formation of C(sp³)?N bonds.     

SbF5/PAF—a novel fluorinating reagent in preparing fluorine compounds

A novel fluorination reagent and catalyst, SbF₅/PAF (porous aluminum fluoride), was prepared by impregnating SbCl₅ into PAF and then treating with anhydrous hydrogen fluoride. The prepared reagent had an excellent catalytic activity in halogen-exchange, and also improved the properties of SbF₅, such as hydroscopicity, corrosion, and toxicity. SbF₅/PAF was successfully used in organic synthesis as a fluorinating reagent, and a fixed bed catalyst for F/Cl exchange.     

Synthesis and characterization of some new aromatic diamine monomers from oxidative coupling of anilines and substituted aniline with 4-amino-N,N-dimethyl aniline

New aromatic diamine monomers prepared from condensation reactions of aniline, p-chloroaniline, p-nitro aniline, p-chloro-m-nitro aniline with 4-amino-N,N-dimethylaniline (2:1) (aniline:reagent) in the presence of potassium dichromate in acidic media yielded new monomers of a highly colored violet and reddish-violet. Mechanism of the reaction of aniline with 4-amino-N,N-dimethylaniline in the presence of potassium dichromate as an oxidant is expected to proceed through nucleophilic substitution reaction, and the mechanism proceeds facilitated a nucleophilic attack of the substituted aniline ring on the –NH₂ group of the reagent; through partial protonation of their –NH₂ group, forming in diamine dye and their identification was confirmed by IR, ¹H NMR, and CHN analyses.     

Synthesis and Reactivity of α‐Cumyl Bromodifluoromethanesulfenate: Application to the Radiosynthesis of [18F]ArylSCF3

A highly reactive electrophilic bromodifluoromethylthiolating reagent, α‐cumyl bromodifluoro‐methanesulfenate 1 , was prepared to allow for direct bromodifluoromethylthiolation of aryl boron reagents. This coupling reaction takes place under copper catalysis, and affords a large range of bromodifluoromethylthiolated arenes. These compounds are amenable to various transformations including halogen exchange with [¹⁸F]KF/K₂₂₂ , a process giving access to [¹⁸F]arylSCF₃ in two steps from the corresponding aryl boronic pinacol esters.     

Ti(Oi‐Pr)4 Mediated Olefination between Julia Reagent and Aldehydes under Mild Conditions: Facile Synthesis of Vinyl Sulfones

A novel Ti(Oi‐Pr)₄ mediated olifination between Julia reagent and aldehydes has been developed. By this method, a series of substituted vinyl sulfones are prepared under mild conditions, all products are exclusively E isomers. All the structures of these compounds were confirmed by ¹H NMR, ¹³C NMR HRMS and IR.