Radical trifluoromethylation of ketone Li enolates

It has generally been believed that highly basic Li enolates cannot be applied as substrates for radical trifluoromethylation due to defluorination of the α-CF₃ product. However, Li enolates can be in fact employed for radical trifluoromethylation. Moreover, the reaction is extremely fast and the minimum reaction time is only ∼1 s.     

Potassium enolates of N,N‐dialkylamides as initiators of anionic polymerization

Stable potassium enolates of N,N‐diethylacetamide [α‐potassio‐N,N‐diethylacetamide ( 1 )], N,N‐diethylpropionamide [α‐potassio‐N,N‐diethylpropionamide ( 2 )], and N,N‐diethylisobutyramide [α‐potassio‐N,N‐diethylisobutyramide ( 3 )] were prepared by the proton abstraction of the corresponding N,N‐diethylamides with diphenylmethylpotassium (Ph₂CHK) or potassium naphthalenide in THF. The relative nucleophilicity of 1 – 3 was estimated to be in the order of 1 < 3 < 2 from the results of the alkylation reaction with methyl iodide. N,N‐diethylacetamide transferred its α‐proton to 2 quantitatively in THF at 0 °C, whereas no reaction occurred between N,N‐diethylisobutyramide and 2 ; this indicated the relative basicity to be 1 < 2 ～ 3 . Anionic polymerizations of N,N‐diethylacrylamide (DEA) and methyl methacrylate were quantitatively initiated with 2 in THF at ?78 °C, whereas the initiation efficiencies of 2 for styrene and 2‐vinylpyridine were about 2 and 67%, respectively. The initiation of DEA with 1 – 3 at ?78 or 0 °C in THF gave poly (DEA)s having broad molecular weight distributions (MWDs; M_w/M_n = 2) and ill‐controlled molecular weights. In contrast, poly(DEA)s of narrow MWDs (M_w/M_n < 1.2) and predicted M_n's were obtained with 2 in the presence of diethylzinc (Et₂Zn) at ?78 °C, whereas the initiations with 1 /Et₂Zn and 3 /Et₂Zn at ?78 °C resulted in poor control of the molecular weights. At the higher temperature of 0 °C, all the binary initiator systems ( 1 – 3 /Et₂Zn) induced controlled polymerizations of DEA in terms of the conversion, molecular weight, and MWD. The poly(DEA)s produced with 1 – 3 /Et₂Zn at 0 °C showed mr‐rich configurations (mr = 76–89%), as observed for the poly(DEA) generated with Ph₂CHK/Et₂Zn. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1260–1271, 2007     

First Isolation and Characterization of the Highly Coordinated Group 14 Enolates: Effects of the Coordination Controls on the Geometry and Tautomerization of Germyl Enolates

The Group 14 enolates play an important part in many organic reactions. Herein, the reduction of an α‐bromo ketone with germanium(II) salts cleanly afforded the corresponding germyl enolate as an isolatable species. This experimental reductive generation of a germyl enolate enabled us to characterize both C‐ and O‐bound tautomers derived from an identical precursor and to unveil the tautomeric mechanisms, including the kinetic parameters and the relative stability of these tautomers, along with confirmation from DFT calculations. Moreover, the highly coordinated germyl enolates were isolated by a stabilization process induced by adding ligands. All products were characterized by NMR spectroscopy and X‐ray crystallography.     

Palladium(II)‐Catalyzed Dehydroboration via Generation of Boron Enolates

The Pd^II‐catalyzed dehydroboration of boron enolates generated from ketones and 9‐iodo‐9‐borabicyclo[3.3.1]nonane was achieved, providing a synthetically versatile protocol from ketones to α,β‐unsaturated ketones. The Pd^II compound employed in this reaction worked catalytically in the presence of Cu(OAc)₂. The high trans‐selectivity of the olefinic moiety was observed. Aryl halide moieties (‐Br and ‐Cl) remained intact for this reaction in spite of the presence of a Pd species. An ester substrate could also be applied when a stoichiometric amount of Pd^II was used. The crossover reactions using boron and silyl enolates revealed that the oxidation reaction is much faster than the Saegusa‐Ito reaction.     

Metal enolates of alpha-CF3 ketones: theoretical guideline, direct generation, and synthetic use

The difficulty as well as the significance of the direct generation of metal enolates of alpha-CF(3) ketones cannot be easily understood by chemists unfamiliar with F. In sharp contrast to the sunny side of non-F, hydrocarbon chemistry, F chemistry has long been overshadowed. Metal enolates of carbonyl compounds are synthetically important in C-C bond-forming reactions. However, the metal enolates of fluorinated carbonyl compounds have been severely limited to alpha-F metal enolates. Alpha-CF(3) metal enolates have generally been recognized as unstable and difficult to prepare because of the facile beta-M-F elimination. However, we have developed a direct generation and synthetic application of alpha-CF(3) metal enolates. Therefore, the present results regarding the direct generation and synthetic use of metal enolates of alpha-CF(3) ketones might be recognized as a real breakthrough for the general use of metal enolates in F chemistry.     

The boron-mediated ketone-ketone aldol reaction

The first examples of the directed, boron-mediated aldol reaction between different ketones are presented. Transformation of a variety of ketones to their corresponding boron enolates with Chx₂BCl/Et₃N, followed by reaction with acceptor ketones in diethyl ether, and oxidation of the resultant boron aldolate (H₂O₂, MeOH/pH 7 buffer), provided the aldol addition products. The reaction was most facile when cyclic ketones were used, with the highest yields obtained for the reaction of boron enolates with cyclohexanone as the acceptor.     

Tandem asymmetric conjugate addition-enolacetates formation of enantiomerically enriched zinc and aluminium enolates

The metal enolates, resulting from the copper-catalyzed enantioselective conjugate addition of organometallic reagents (Et₂Zn or R₃Al) to cyclic and acyclic enones are quantitatively trapped as enolacetates with acetic anhydride.     

Dicationic (BINAP)palladium-catalyzed enantioselective aldol reaction of aldehydes with a silyl enol ether: a simplified practical procedure

The dicationic ((R)-BINAP)palladium-catalyzed enantioselective aldol reaction of benzaldehyde with 1-phenyl-1-trimethylsilylethene has been reinvestigated regarding the reaction conditions in the presence of ((R)-BINAP)palladium chloride and AgSbF₆ with 3 Å molecular sieves. The simplified practical procedure with 1 mol % catalyst loading realized the high performance of 98% yield and 76% ee with reliable reproducibility.     

Boron trifluoride-catalyzed reaction of alkyl fluoride with silyl enolate, allylsilane, and hydrosilane

Alkylation of silyl enolates with tert-alkyl or allylic fluorides proceeds smoothly in the presence of a catalytic amount of boron trifluoride to afford the corresponding carbonyl compounds. Allylation and reduction of alkyl fluorides with allylsilane and hydrosilane, respectively, occur under BF₃ catalysis.     

Zinc enolates: C- or O-metallation?

Two methods have been used for the generation of zinc enolates: the reaction of EtZnOMe with enol acetates, and that of lithium enolates with zinc chloride. Most of the zinc compounds prepared proved to be very reactive towards carbonyl functions, and so they cannot be isolated from the EtZnOMe/enol acetate system. The final products of these reactions are polymerisation and self-condensation products and β-diketonates, the latter being formed by condensation reactions of the zinc enolates with an acetate molecule. The structure of [EtZnOMe·Zn(Pac)₂]₂ (HPac = pivaloylacetone, (CH₃)₃CCOCH₂COCH₃), isolated in 20% yield from the reaction of EtZnOMe with CH₃COOC(t-Bu)CH₂, was determined by X-ray diffraction analysis. The compound forms monoclinic crystals, space group P2₁/c, with two dimers in a cell of dimensions a 11.677(4), b 18.299(9) and c 12.719(5) Å and β 117.26(3)°. The structure closely resembles that of the known complex [PhZnOPh·Zn(Pac)₂]₂.The complications involving reactions of zinc enolates with enol acetates were avoided by treating lithium enolates with zinc chloride. Polymerization and self-condensation could be prevented by using the very bulky enolate LiOC(t-Bu)CMe₂. In this way, the corresponding stable zinc enolate RZnCl·THF was obtained as a dissociating dimer. No replacement of the second chlorine atom by an enolate group occurred even when a large excess of lithium enolate was used.The reactivity of the zinc enolates suggests that they contain both zinccarbon and zincoxygen bonds. They are assumed to have a cyclic structure which resembles that of the Reformatsky reagent.     

Structural architectures of charge-assisted,hydrogen-bonded, 2D layered amine⋯tetraphosphonate and zinc⋯tetraphosphonate ionic materials

The synthesis, characterization and structural analyses of ionic amine-phosphonate and hydrated metal ion-phosphonate compounds are reported. These are (en)(HDTMP), (NH₄)(EDTMP), Zn(H₂O)₆(TDTMP) (en = ethylenediamine, HDTMP = hexamethylenediamine-tetrakis(methylenephosphonate), EDTMP = diethylenediamine-tetrakis(methylenephosphonate), TDTMP = tetramethylenediamine-tetrakis(methylenephosphonate)). All three compounds are composed of discrete anions and cations, stabilized by intricate networks of hydrogen bonds, and form 2D layered architectures.     

Supramolecular networks through second-sphere coordination based on 1D metal-4,4′-dipyridyldisulfide coordination polymers and hydrogenfumarate or sulfonate anions

Four hydrogen-bonded assemblies of formula [M(dpds)₂(OH₂)₂]A₂·nH₂O (A = anion) are described. These assemblies result from the second-sphere coordination interactions between the 1D coordination polymers [M(dpds)₂(OH₂)₂]²⁺, M = Zn(II) and Cu(II), dpds = 4,4′-dipyridyldisulfide, and the pyridine-3-sulfonate (3pySO₃⁻) or hydrogenfumarate (Hfum⁻) anions. Significantly, supramolecular structural variations are observed depending on the presence of water lattice molecules, which formed discrete aggregates when the Hfum⁻ anion was used. The effects of geometrical variations in the building blocks are also evident on using Jahn-Teller-distorted divalent Cu(II) ions or regular octahedral species based on Zn(II) ions. The second-sphere effects on the stabilization of the compounds are illustrated by TGA experiments.     

Palladium-catalyzed asymmetric allylic alkylation of acyclic ketones for synthesis of 2,2-disubsituted pyrrolidine derivatives

Palladium-catalyzed asymmetric allylic alkylation of acyclic ketones represents a significant challenge in organic synthesis. We report herein that the synthesis of chiral 2,2-disubsituted pyrrolidines from acyclic ketones has been accomplished by using catalytic asymmetric method in the presence of Pd(dba)₂ and (R)-binap ligand. Theses reactions occur between allyl methyl carbonate and unstabilized acyclic lithium enolates to provide the products in moderate to good enantioselectivity (up to 81% ee).     

Homoleptic [M(XeF2)6] cations of copper(II) and zinc(II)—Syntheses and crystal structures of [M(XeF2)6](SbF6)2 (M = Cu, Zn)

[Cu(XeF₂)₆](SbF₆)₂ crystallizes in the rhombohedral symmetry with a = 1003.6(2) pm, c = 2246.5(12) pm at 200 K and Z = 3, space group (No. 148). [Zn(XeF₂)₆](SbF₆)₂ is isostructural to [Cu(XeF₂)₆](SbF₆)₂ with a = 1007(2) pm and c = 2243(6) pm. The structures are characterized by isolated homoleptic [M(XeF₂)₆]²⁺ (M = Cu, Zn) cations and of [SbF₆]⁻ octahedra.Reactions of M(SbF₆)₂ (M = Cu, Zn) with XeF₂ in anhydrous hydrogen fluoride (aHF) and reactions of MF₂ with Xe₂F₃SbF₆ in aHF always yield a mixture of [M(XeF₂)₆](SbF₆)₂, Xe₂F₃SbF₆ and MF₂.     

Similarities and differences of epoxide, aldehyde and peroxide initiators for Cp2TiCl-catalyzed styrene living radical polymerizations

Cp₂TiCl is the first example of a single electron transfer (SET) agent that both provides initiating radicals from three different types of functionalities (i.e. radical ring opening of epoxides and reduction of aldehydes and peroxides) and doubles as mediator for the living radical polymerization of styrene (St) by reversibly endcapping the growing polymer chains. An initiator (I) comparison was performed using 1,4-butanediol diglycidyl ether (BDE), benzaldehyde (BA) and benzoyl peroxide (BPO) as models. The investigation of the effect of reaction variables was carried out over a wide range of experimental conditions ([Cp₂TiCl₂]/[I] = 0.5/1-4/1; [Zn]/[Cp₂TiCl₂] = 0.5/1-3/1, [St]/[I] = 50/1-400/1 and T = 60-130 °C) to reveal living polymerization features such as a linear dependence of molecular weight on conversion and narrow molecular weight distribution (M_w/M_n) for each initiator class. However, progressively lower polydispersities and larger initiator efficiencies are obtained with increasing the [Cp₂TiCl₂]/[I] and [Zn]/[Cp₂TiCl₂] ratios and with decreasing temperature. Accordingly, optimum conditions correspond to [St]/[I]/[Cp₂TiCl₂]/[Zn] = [50-200]/[1]/[2-3]/[4-6] at 70-90 °C. By contrast to peroxides, aldehydes and the more reactive epoxides provide alcohol end groups useful in block or graft copolymers synthesis.     

Spectral, thermal and X-ray studies on some new bis-hydrazine metal glyoxylates and bis-hydrazine mixed metal glyoxylates

Bis-hydrazine complexes of metal glyoxylates and mixed metal glyoxylates of 3d-metal ions of the formula M(OOCCHO)₂(N₂H₄)₂, where M = Mg, Mn, Co, Ni, Cu, Zn or Cd and M_1/3Co_2/3(OOCCHO)₂(N₂H₄)₂, where M = Mg, Mn, Ni, Zn or Cd, respectively, have been prepared and studied. The compositions of the complexes have been determined by chemical analyses. The magnetic moments and electronic spectra suggest a high-spin octahedral geometry for the metal complexes. Infrared spectral data indicate the bidentate bridging by hydrazine molecules and monodentate coordination by glyoxylate ions in both the metal and mixed metal compounds. Thermogravimetry and differential thermal analyses in air have been used to study the thermal behaviour of the complexes. The simultaneous TG-DTA traces of all the complexes show multi-step degradation and the final products are found to be the respective metal oxides in the case of metal complexes and metal cobaltites in the case of mixed metal complexes. The final residues were identified by their X-ray powder diffraction patterns. X-ray powder diffraction patterns of the complexes including mixed metal complexes are almost superimposable with in each of the series indicating isomorphism. The metal cobaltites MCo₂O₄, where M = Mg, Mn, Ni, Zn or Cd were also prepared by decomposing the respective mixed metal complex in a pre-heated silica crucible at about 300 °C, and their identities were confirmed by chemical analyses, infrared spectra and X-ray powder diffraction.     

Sensors based on galvanic cell generated electrochemiluminescence and its application

In this paper, a novel electrochemiluminescence (ECL) imaging sensor array was developed for determination of hydrogen peroxide (H₂O₂), which was based on Cu/Zn alloy galvanic cell generated ECL. In alkaline solution, Cu/Zn galvanic cell was formed because of corrosion effect, the galvanic cell could supply stable potential for ECL generation of luminol, and the weak ECL emission could be enhanced by H₂O₂. The galvanic cell sensor array was designed by putting Cu/Zn alloy in 96-well microtiter plates separately. The relative ECL intensity was proportional with the concentration of hydrogen peroxide in the range of 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol l⁻¹ and the detection limit was 3.0 × 10⁻⁷ mol l⁻¹ (3σ), the relative standard deviation (R.S.D.) for 11 parallel measurements of 1.0 × 10⁻⁵ mol l⁻¹ H₂O₂ was 4.0%.     

Direct α‐Siladifluoromethylation of Lithium Enolates with Ruppert‐Prakash Reagent via CF Bond Activation

The direct α‐siladifluoromethylation of lithium enolates with the Ruppert–Prakash reagent (CF₃TMS) is shown to construct the tertiary and quaternary carbon centers. The Ruppert–Prakash reagent, which is versatile for various trifluoromethylation as a trifluoromethyl anion (CF₃^?) equivalent, can be employed as a siladifluoromethyl cation (TMSCF₂⁺) equivalent by C?F bond activation due to the strong interaction between lithium and fluorine atoms.     

Enantioselective conjugate addition of dialkylzinc to cyclic enones catalyzed by chiral binaphthyldiamine-copper(I) complexes

The enantioselective conjugate addition of dialkylzinc (R₂Zn) to cyclic enones was examined using chiral binaphthyldiamine-copper(I) catalysts. Under the present reaction conditions, chiral C₂-symmetric [RZn(II)]₂-diamine-Cu(I) complexes were formed from chiral binaphthyldiamine, R₂Zn, and copper(I or II) chloride in situ. The reaction of 2-cyclohexenone with Et₂Zn proceeded smoothly in the presence of the corresponding chiral copper(I) complex (5 mol %) and achiral 2,6-diphenylaniline (10 mol %), and the desired Et-adduct was obtained with up to 76% ee in 95% yield.     

Evaluation of V, Ir, Ru, V-Ir, V-Ru, and W-V as permanent chemical modifiers for the determination of cadmium, lead, and zinc in botanic and biological slurries by electrothermal atomic absorption spectrometry

Permanent modifiers (V, Ir, Ru, V-Ir, V-Ru, and W-V) thermally coated on to platforms of pyrolytic graphite tubes were employed for the determination of Cd, Pb, and Zn in botanic and biological slurries by electrothermal atomic absorption spectrometry (ETAAS). Conventional Pd + Mg(NO₃)₂ modifier mixture was also used for the determination of analytes in slurries and digested samples. Optimum masses and mass ratios of permanent modifiers for Cd, Pb, and Zn in slurry sample solutions were investigated. The 280 μg of V, 280 μg of V + 200 μg of Ir, 280 μg of V + 200 μg of Ru or 240 μg of W + 280 μg of V in 0.2% (v/v) Triton X-100 plus 0.5% (v/v) HNO₃ mixture was found as efficient as 5 μg of Pd + 3 μg of Mg(NO₃)₂ modifier mixture for obtaining thermal stabilization, and for obtaining best recoveries. Optimization conditions of analytes, such as pyrolysis and atomization temperature, characteristic masses and detection limits, and atomization and background peak profiles were studied with permanent and 5 μg of Pd + 3 μg of Mg(NO₃)₂ conventional modifiers and compared with each other. The permanent V-Ir, V-Ru, and W-V modifiers remained stable for approximately 250-300 firings when 20 μl of slurries and digested samples were delivered into the atomizer. In addition, the mixed permanent modifiers increase the tube lifetime by 50-95% when compared with untreated platforms. The characteristic masses and detection limits of analytes (dilution factor of 125 ml g⁻¹) obtained with V-Ir based on integrated absorbance as example for 0.8% (m/v) slurries were 1.0 pg and 3 ng g⁻¹ for Cd, 18 pg and 17 ng g⁻¹ for Pb, and 0.7 pg and 4 ng g⁻¹ for Zn, respectively. The results of analytes obtained by employing V-Ir, V-Ru, and W-V permanent modifier mixtures in botanic and biological certified and standard reference materials were in agreement with the certified values of reference materials.