Enantioselective glyoxylate-ene reaction using a novel spiro bis(isoxazoline) ligand in copper catalysis

Novel chiral spiro bis(isoxazoline) ligands 3 and 4 are synthesized from an optically active olefin. The Cu(II)-spiro bis(isoxazoline) complex prepared in situ from Cu(OTf)₂ and 3 promoted the glyoxylate-ene reaction in high yield and moderate enantioselectivity (up to 70%).     

Design and synthesis of chiral hybrid spiro (isoxazole–isoxazoline) ligands

Novel chiral hybrid ligands containing an unsymmetrical spiro[4.5]decane skeleton with isoxazole and isoxazoline as the two coordinating units have been synthesized. Pd complexes of these ligands were found to be effective in activating olefins towards enantioselective tandem cyclization of a dialkenyl alcohol, providing the cyclized products in up to 97% ee.     

Studies in werner clathrates. Part 2. Structures of bis (isothiocyanato) tetra (4-phenylpyridine) nickel (II)· 4-dimethylsulphoxide,bis (isothiocyanato) tetra (3-methylpyridine) nickel (II)· chloroform and bis (isothiocyanato) tetra (3,5-dimethylpyridine) nickel (II)

The structures of Ni(NCS)₂(4-PhPy)₄·4DMSO and Ni(NCS)₂(3-MePy)₄·CHCl₃ have been elucidated. Movement of guest molecules through channels in the host structure was simulated by potential energy calculations. Ni(NCS)₂(3,5-diMePy)₄ does not form inclusion compounds. An intra-molecular potential energy study shows that theortho-hydrogens on the 3,5-dimethylpyridine ligands control the conformation of the molecule. The same result is obtained with the 4-methylpyridine ligand, which suggests that the extent of rotation of substituted pyridines about the Ni–N bounds is not a factor governing clathrate formation. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82030 (43 pages).     

Synthesis of spiro bis(1,2,3-triazolium) salts as chiral ionic liquids

Unique chiral spiro ionic liquids based on 1,2,3-triazolium salts were synthesized via an intramolecular double Huisgen reaction. The optical resolution of the liquid precursors and subsequent dialkylations leads to chiral spiro triazolium salts on a gram scale.     

The first enantioselective intramolecular aminocarbonylation of alkenes promoted by Pd(II)-spiro bis(isoxazoline) catalyst

The highly ligand acceleration effect of spiro bis(isoxazoline) ligand (SPRIX) on the Pd(II)-catalyzed intramolecular aminocarbonylation of alkenyl amine derivatives was realized. Furthermore, the chiral Pd(II)-SPRIX catalyst accomplished the first enantioselective intramolecular aminocarbonylation. The reaction of N-(2,2-dimethyl-pent-4-enyl)-p-toluenesulfonamide in the presence of Pd(II)-SPRIX catalyst and p-benzoquinone in methanol under a carbon monoxide atmosphere afforded [4,4-dimethyl-1-(p-toluene-sulfonyl)-pyrrolidin-2-yl]-acetic acid methyl ester in good yield with moderate enantioselectivity.     

Carbohydrate-based spiro bis(isoxazolines): synthesis and evaluation in asymmetric catalysis

Two carbohydrate-based spiro bis(isoxazolines) were synthesized via 1,3-dipolar cycloaddition from peracetylated methylene exo-glucal and the corresponding bis(arylnitrile oxide). The bis(cycloadducts) were then evaluated as ligands for enantioselective catalytic reactions. The Pd-catalyzed Tsuji-Trost reaction between a malonate and an allylic acetate did not provide good results. The poor conversion observed can be attributed to the rearrangement of the ligand in the reaction mixture to afford the corresponding ring-opened isoxazole which has been characterized. Both ligands were also evaluated in Cu(I)-catalyzed asymmetric imine alkynylation and afforded the product in good yield and modest enantioselectivity.     

Optical properties of bis(pyrazino)tetrathiafulvalene salts

The optical reflectance and absorption spectra of (BPTTF)₂BF₄[where BPTTF is bis(pyrazino) tetrathiafulvalene] and similar salts are reported for a wide spectral region.     

Design and synthesis of spiro bis(1,2,3-triazolium) salts as chiral ionic liquids

Room temperature chiral spiro ionic liquids 1 and 2 based on 1,2,3-triazolium salts, were synthesized via an intramolecular double Huisgen reaction. The preparation of the enantiomerically pure spiro triazolium salts was achieved by resolution by HPLC using a chiral stationary phase column and subsequent N-dialkylations of spiro triazoles 6 and 10.     

Optical and electrophysical properties of metal complexes of tetra(1,4-dithiacyclohexeno)porphyrazine

The optical and electrophysical characteristics of metal complexes of tetra-(1,4-dithiacyclohexeno)porphyrazine were measured. The presence of 1,4-dithi-acyclohexene rings in the molecules of the investigated compounds leads to the appearance of bands corresponding to an n * transition in the absorption spectra. The positions of the long-wave bands corresponding to a * transition are determined by the nature of the metal. All of the complexes have semiconductor properties; the specific electrical conductivities range from 10^–11 to 10^{–9 –1}·cm^–1.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1276–1279, September, 1986.     

Optical properties of bis(cyclopentadienyl)magnesium: excimer-type luminescence of the bis(cyclopentadienyl) ligand frame

The electronic spectra of solid MgCp₂ (Cp = cyclopentadienyl) show features which indicate the presence of intramolecular interligand interactions. The fluorescence of MgCp₂ (λ_max = 363 nm) undergoes a considerable Stokes shift which is apparently caused by a bonding attraction between both Cp rings in the excited state. An additional phosphorescence of the (Cp⁻)₂ fragment (λ_max = 535 nm) appears at 77 K.     

Synthesis of photoreactive isopropyl-substituted poly(phenylene ether ether ketone)

Isopropyl substituted poly(phenylene ether ether ketone) with a high molecular weight was prepared by nucleophilic substitution reaction of isopropyl-substituted difluoro diaryl ether with hydroquinone. This polymer was amorphous and soluble in common organic solvents, such as THF, chloroform, and cyclohexanone. Thermogravimetry of the polymer showed good thermal stability, indicating that a 10% weight loss of the polymer was observed at 470°C in nitrogen. The glass transition temperature of the polymer was 145°C. The polymer had a broad UV absorption band over 250–380 nm. The polymer acted as a photosensitive resist of negative type for UV radiation. The resist had a sensitivity of 40 mJ/cm² and a contrast of 2.8, when it was developed with DMF at room temperature. © 1997 John Wiley & Sons, Inc.     

Optical properties of a tetradentate bis(beta-diketonate) europium(III) complex

Eu₂(BPOPB)₃H₂O, an europium complex chelated with bis(β-diketone), was synthesized. Its properties have been investigated by absorption spectrum, emission spectrum and luminescence lifetime measurement. The complex displays strong red luminescence upon irradiation at the ligand band around 355 nm, which indicates that the bis-β-diketonate ligand BPOPB is an efficient sensitizer. The Judd–Ofelt parameters obtained from the emission spectrum of Eu₂(BPOPB)₃H₂O have been used to calculate the total spontaneous emission probabilities (A), the radiative lifetime (τ_rad), the fluorescence branching ratio (β) and the stimulated emission cross-sections (σ). The luminescence lifetimes are determined to be 402 and 169 μs for Eu₂(BPOPB)₃H₂O and Eu(DBM)₃(H₂O)₂, respectively. The relationship between the structures of rare-earth complexes and luminescence lifetimes was analyzed. The radiative properties reveal that Eu₂(BPOPB)₃H₂O is potential to be an efficient luminescent material.     

Radial tetra(ferrocenyl)- and tetra(cymantrenyl)cyclobutadienecobalt complexes: Synthesis and structures

Novel radial tetra(ferrocenyl)- and tetra(cymantrenyl)cyclobutadienecobalt complexes were prepared by metal carbonyls free protocol of [2 + 2] cycloaddition reaction of 1,2-diferrocenyl- or 1,2-dicymantrenylethynes with chlorotris(triphenylphospine)cobalt(I) and carboethoxycyclopentadienide sodium with good yields. The molecular structure of these products was confirmed with X-ray analysis, and their electrochemical behavior was studied.     

Chiral bis(mandelato)borate salts for resolution via metathesis crystallization

Spiroborate anions have potential for crystallization or resolution and chiral bis(mandelato)borate anions can be used for the efficient resolution of a diverse range of racemic cations via diastereomeric salt formation. The syntheses, X‐ray crystal structures and solubilities of three chiral bis(mandelato)borate salts, namely poly[[aqua‐μ₃‐bis[(R )‐mandelato]borato‐lithium(I)] monohydrate], [Li(C₁₆H₁₂BO₆)(H₂O)]_n or Li[B(R‐Man)₂]·H₂O, (1), ammonium bis[(R )‐mandelato]borate, NH₄⁺·C₁₆H₁₂BO₆⁻ or NH₄[B(R‐Man)₂], (2), and tetra‐n‐butylammonium bis[(R )‐mandelato]borate, C₁₆H₃₆N⁺·C₁₆H₁₂BO₆⁻ or NBu₄[B(R‐Man)₂], (3), are reported. They all have a B_S configuration and show a reasonably well‐conserved anion geometry. The main conformational variation is the orientation of the two phenyl groups, supporting the idea that [B(Man)₂]⁻ is a semi‐rigid anion. The salts are differentially soluble in a range of solvents, meaning they could be useful as reagents for resolution via a metathesis crystallization approach.     

Optical resolution of tris (acetylacetonato) aluminium(III) by low temperature chromatography

Al(acac)₃ was resolved into optical isomers with a high yield by chromatography on D-lactose/Al₂O₃ at 210 K and the circular dichroism (CD) spectra of the enantiomers were measured.The absolute configuration was established both by using a locally excited transition in the ligand and by correlating the retention order due to the adsorption with that of an equivalent complex with known configuration. The nomenclature (CD+)₃₀₃-Al(acac)₃ is suggested for the enantiomer exhibiting positive CD at 303 nm. This enantiomer has the absolute configuration

From the observed racemisation rate constants at elevated temperatures activation parameters were estimated: E_α = 131 ± 5 kJ mol⁻¹, ΔH = 130 ± 5 kJ mol⁻¹, ΔS = 220 ± 16 J K⁻¹ mol⁻¹.Al(acac)₃ is the first example of a compound that has been optically resolved by low temperature chromatography (LTC).