Yiying Zheng - Academia.edu (original) (raw)

Papers by Yiying Zheng

Journal of the American Chemical Society

General information Unless otherwise stated, all reagents were purchased from commercial supplier... more General information Unless otherwise stated, all reagents were purchased from commercial suppliers and used without further purification. All solvents used in the reactions were distilled from appropriate drying agents prior to use. Reactions were monitored by thin layer chromatography (TLC) on silica gel pre-coated plastic sheets (0.2 mm, Macherey-Nagel). Visualization was accomplished by irradiation with UV light at 254 nm and/or phosphomolybdic acid (PMA) stain. Column chromatography was performed on Merck silica gel (60, particle size 0.040-0.063 mm). Proton and carbon NMR spectra were recorded on Bruker AV-500, Bruker AV-400 or Bruker AV-300 spectrometer in deuterated solvents. Proton chemical shifts are reported in ppm (δ) relative to tetramethylsilane (TMS) with the solvent resonance employed as the internal standard (CDCl 3 δ 7.26 ppm; CD 2 Cl 2 δ 5.32 ppm). Data are reported as follows: chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, p = pentet, s = sextet, h = heptet, m = multiplet, br = broad), coupling constants (Hz) and integration. 13 C chemical shifts are reported in ppm from tetramethylsilane (TMS) with the solvent resonance as the internal standard (CDCl 3 δ 77.16 ppm; CD 2 Cl 2 δ 53.84 ppm). Proton and carbon NMR spectra of the major diastereomer of the product 2 are reported. High resolution mass spectra were determined on a Bruker APEX III FTMS (7 T magnet). Optical rotations were determined with Autopol IV polarimeter (Rudolph Research Analytical) at 589 nm and 25 °C. Data are reported as follows: [α] λ temp , concentration (c in g/100 mL), and solvent. Enantiomeric ratios (e.r.) of the cyclic homoallylic alcohols were determined by GC or HPLC analysis employing a chiral stationary phase column specified in the individual experiment, by comparing the samples with the appropriate racemic mixtures.

Advanced Synthesis & Catalysis, 2010

The mechanism of the asymmetric Simmons-Smith cyclopropanation for unfunctionalized olefins was i... more The mechanism of the asymmetric Simmons-Smith cyclopropanation for unfunctionalized olefins was investigated using density functional theory (DFT) methods. The calculated results of model reactions showed that the coordinated Lewis acidic zinc halide ZnX 2 (X = Cl, I) and/or halo-A C H T U N G T R E N N U N G methylzinc halide XZnCH 2 X in the catalyst play an important role in the enantioselectivity. The catalyst not only forms the ring with the substance in the reaction centre, but also establishes two steric repulsions that can lead to an explanation for the high enantioselectivity. Hence, these results highlight some important insights for the prerequisites of an effective catalyst and a proper substrate towards high enantioselectivity for this kind of reaction.

Journal of the American Chemical Society

General information Unless otherwise stated, all reagents were purchased from commercial supplier... more General information Unless otherwise stated, all reagents were purchased from commercial suppliers and used without further purification. All solvents used in the reactions were distilled from appropriate drying agents prior to use. Reactions were monitored by thin layer chromatography (TLC) on silica gel pre-coated plastic sheets (0.2 mm, Macherey-Nagel). Visualization was accomplished by irradiation with UV light at 254 nm and/or phosphomolybdic acid (PMA) stain. Column chromatography was performed on Merck silica gel (60, particle size 0.040-0.063 mm). Proton and carbon NMR spectra were recorded on Bruker AV-500, Bruker AV-400 or Bruker AV-300 spectrometer in deuterated solvents. Proton chemical shifts are reported in ppm (δ) relative to tetramethylsilane (TMS) with the solvent resonance employed as the internal standard (CDCl 3 δ 7.26 ppm; CD 2 Cl 2 δ 5.32 ppm). Data are reported as follows: chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, p = pentet, s = sextet, h = heptet, m = multiplet, br = broad), coupling constants (Hz) and integration. 13 C chemical shifts are reported in ppm from tetramethylsilane (TMS) with the solvent resonance as the internal standard (CDCl 3 δ 77.16 ppm; CD 2 Cl 2 δ 53.84 ppm). Proton and carbon NMR spectra of the major diastereomer of the product 2 are reported. High resolution mass spectra were determined on a Bruker APEX III FTMS (7 T magnet). Optical rotations were determined with Autopol IV polarimeter (Rudolph Research Analytical) at 589 nm and 25 °C. Data are reported as follows: [α] λ temp , concentration (c in g/100 mL), and solvent. Enantiomeric ratios (e.r.) of the cyclic homoallylic alcohols were determined by GC or HPLC analysis employing a chiral stationary phase column specified in the individual experiment, by comparing the samples with the appropriate racemic mixtures.

Advanced Synthesis & Catalysis, 2010

The mechanism of the asymmetric Simmons-Smith cyclopropanation for unfunctionalized olefins was i... more The mechanism of the asymmetric Simmons-Smith cyclopropanation for unfunctionalized olefins was investigated using density functional theory (DFT) methods. The calculated results of model reactions showed that the coordinated Lewis acidic zinc halide ZnX 2 (X = Cl, I) and/or halo-A C H T U N G T R E N N U N G methylzinc halide XZnCH 2 X in the catalyst play an important role in the enantioselectivity. The catalyst not only forms the ring with the substance in the reaction centre, but also establishes two steric repulsions that can lead to an explanation for the high enantioselectivity. Hence, these results highlight some important insights for the prerequisites of an effective catalyst and a proper substrate towards high enantioselectivity for this kind of reaction.