The reduction of TiCl4(THF)2 with Al in CH2Cl2 gave a green solution of [Ti2(μ-Cl)2Cl4· (THF)4] (1) which was found to promote the reductive homocoupling of aromatic aldehydes to yield symmetrical 1, 2-diols wit...The reduction of TiCl4(THF)2 with Al in CH2Cl2 gave a green solution of [Ti2(μ-Cl)2Cl4· (THF)4] (1) which was found to promote the reductive homocoupling of aromatic aldehydes to yield symmetrical 1, 2-diols with high diasterepselectivities.展开更多
Pinacol coupling reactions of aromatic aldehydes and ketones were carded out using Nd-36% HOAc-CH2Cl2 system with stirring at r. t. for 4 h （in 14-70% yield）. The reactions in the same system gave pinacols in 10-93%...Pinacol coupling reactions of aromatic aldehydes and ketones were carded out using Nd-36% HOAc-CH2Cl2 system with stirring at r. t. for 4 h （in 14-70% yield）. The reactions in the same system gave pinacols in 10-93% yield under ultrasound irradiation at r. t. for 2 h.展开更多
Asymmetric pinacol coupling of aromatic aldehydes catalyzed by chiral diamines/low valent titanium complexes gave corresponding pinacols in good yields with high diastereoselectivity and moderate enantioselectivities.
A colorimetric method for the direct determination of hydrogen peroxide in aqueous solution is described. H2O2 stoichiometrically converts 4-nitrophenyl boronic acid or 4-nitrophenyl boronic acid pinacol ester into 4-...A colorimetric method for the direct determination of hydrogen peroxide in aqueous solution is described. H2O2 stoichiometrically converts 4-nitrophenyl boronic acid or 4-nitrophenyl boronic acid pinacol ester into 4-nitrophenol, which can be quantified by measuring the absorption at 400 nm in neutral or basic media. The reactions proceed fast under basic conditions and complete in 2 minutes to at pH 11 and 80?C. The linear range for the colorimetric method extends beyond 1.0 to 40 μM H2O2, and the limit of detection is ~1.0 μM H2O2. This method offers a convenient and practical process for rapid determination of hydrogen peroxide in aqueous media. Compared to many other techniques in H2O2 detection, this process is a direct measurement of H2O2, and is relatively unaffected by the presence of various salts, metal ions and the chelator EDTA.展开更多
A convenient pinacol coupling of aromatic aldehydes and aryl methyl ketones has been achieved with high yields by aluminum powder in the presence of oxalic acid in water. However, the diastereoselectivities of pinacol...A convenient pinacol coupling of aromatic aldehydes and aryl methyl ketones has been achieved with high yields by aluminum powder in the presence of oxalic acid in water. However, the diastereoselectivities of pinacols were not satisfying, and most aliphatic aldehydes and diaryl ketones have been found to be unreactive under the same conditions.展开更多
Pinacol coupling reactions catalyzed by active zinc revealed high activity and extensive suitability. The efficiency of the reaction was improved apparently owing to decreasing reductive potential of zinc. In addition...Pinacol coupling reactions catalyzed by active zinc revealed high activity and extensive suitability. The efficiency of the reaction was improved apparently owing to decreasing reductive potential of zinc. In addition, the results indicated that the zinc activity has a direct relation to the coupling reactivity compared to untreated zinc or other general active zinc.展开更多
Asymmetric pinacol coupling of aromatic aldehydes with TiCl4-Zn in the presence of enantiopure squaric acid amidoalcohols afforded 1, 2-diols in excellent yields with high dl- diastereoselectivities and enantioselecti...Asymmetric pinacol coupling of aromatic aldehydes with TiCl4-Zn in the presence of enantiopure squaric acid amidoalcohols afforded 1, 2-diols in excellent yields with high dl- diastereoselectivities and enantioselectivities in the range of 46-89% ee. Some factors influencing dl-diastereoselectivity and enantioselectivity were discussed.展开更多
Asymmetric pinacol coupling of aromatic aldehydes mediated by low valent titanium complexes of chiral ligands derived from natural tartaric acid provided corresponding pinacols in good yields with excellent diastereo-...Asymmetric pinacol coupling of aromatic aldehydes mediated by low valent titanium complexes of chiral ligands derived from natural tartaric acid provided corresponding pinacols in good yields with excellent diastereo-selectivities and moderate enantioselectivities.展开更多
In the presence of a catalytic amount of iodine, metallic samarium mediated pinacol coupling of carbonyl compounds has been carried out under saturated aqueous Nl&Cl-THF conditions at mom temperature. It gives cor...In the presence of a catalytic amount of iodine, metallic samarium mediated pinacol coupling of carbonyl compounds has been carried out under saturated aqueous Nl&Cl-THF conditions at mom temperature. It gives corresponding 1,2-diols in god yields.展开更多
An environmentally benign method to accelerate the pinacol rearrangement in high temperature liquid water by the addition of CO2 was proposed.The effects of CO2 initial pressure and temperature on the kinetics of pina...An environmentally benign method to accelerate the pinacol rearrangement in high temperature liquid water by the addition of CO2 was proposed.The effects of CO2 initial pressure and temperature on the kinetics of pinacol rearrangement were studied.The experimental results showed that the reaction rate could be greatly increased with the addition of CO2.The activation energies evaluated were 81.1 kJ·mol-1 without CO2,and 87.1 kJ·mol-1 with CO2 initial pressure at 0.2 MPa,which showed no significant difference.The main by-product was confirmed to be 2,3-dimethyl-3-butadiene by GC/MS and the possible reaction mechanism was proposed.展开更多
文摘The reduction of TiCl4(THF)2 with Al in CH2Cl2 gave a green solution of [Ti2(μ-Cl)2Cl4· (THF)4] (1) which was found to promote the reductive homocoupling of aromatic aldehydes to yield symmetrical 1, 2-diols with high diasterepselectivities.
基金supported by the Natural Science Foundation of Hebei Province(203107)the Science Foundation of Hebei Langfang Normal College(200517).
文摘Pinacol coupling reactions of aromatic aldehydes and ketones were carded out using Nd-36% HOAc-CH2Cl2 system with stirring at r. t. for 4 h （in 14-70% yield）. The reactions in the same system gave pinacols in 10-93% yield under ultrasound irradiation at r. t. for 2 h.
基金ProjectsupportedbytheNationalNaturalScienceFoundationofChina (No .2 9872 0 3 5 )
文摘Asymmetric pinacol coupling of aromatic aldehydes catalyzed by chiral diamines/low valent titanium complexes gave corresponding pinacols in good yields with high diastereoselectivity and moderate enantioselectivities.
文摘A colorimetric method for the direct determination of hydrogen peroxide in aqueous solution is described. H2O2 stoichiometrically converts 4-nitrophenyl boronic acid or 4-nitrophenyl boronic acid pinacol ester into 4-nitrophenol, which can be quantified by measuring the absorption at 400 nm in neutral or basic media. The reactions proceed fast under basic conditions and complete in 2 minutes to at pH 11 and 80?C. The linear range for the colorimetric method extends beyond 1.0 to 40 μM H2O2, and the limit of detection is ~1.0 μM H2O2. This method offers a convenient and practical process for rapid determination of hydrogen peroxide in aqueous media. Compared to many other techniques in H2O2 detection, this process is a direct measurement of H2O2, and is relatively unaffected by the presence of various salts, metal ions and the chelator EDTA.
文摘A convenient pinacol coupling of aromatic aldehydes and aryl methyl ketones has been achieved with high yields by aluminum powder in the presence of oxalic acid in water. However, the diastereoselectivities of pinacols were not satisfying, and most aliphatic aldehydes and diaryl ketones have been found to be unreactive under the same conditions.
基金supported by the National Natural Science Foundation of China(No.20472079)
文摘Pinacol coupling reactions catalyzed by active zinc revealed high activity and extensive suitability. The efficiency of the reaction was improved apparently owing to decreasing reductive potential of zinc. In addition, the results indicated that the zinc activity has a direct relation to the coupling reactivity compared to untreated zinc or other general active zinc.
文摘Asymmetric pinacol coupling of aromatic aldehydes with TiCl4-Zn in the presence of enantiopure squaric acid amidoalcohols afforded 1, 2-diols in excellent yields with high dl- diastereoselectivities and enantioselectivities in the range of 46-89% ee. Some factors influencing dl-diastereoselectivity and enantioselectivity were discussed.
基金the National Natural Science Foundation (No. 20172049) of China.
文摘Asymmetric pinacol coupling of aromatic aldehydes mediated by low valent titanium complexes of chiral ligands derived from natural tartaric acid provided corresponding pinacols in good yields with excellent diastereo-selectivities and moderate enantioselectivities.
基金National Natural Science Foundation of China, the NSF of Zhejiang Province, China,Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.
文摘In the presence of a catalytic amount of iodine, metallic samarium mediated pinacol coupling of carbonyl compounds has been carried out under saturated aqueous Nl&Cl-THF conditions at mom temperature. It gives corresponding 1,2-diols in god yields.
文摘An environmentally benign method to accelerate the pinacol rearrangement in high temperature liquid water by the addition of CO2 was proposed.The effects of CO2 initial pressure and temperature on the kinetics of pinacol rearrangement were studied.The experimental results showed that the reaction rate could be greatly increased with the addition of CO2.The activation energies evaluated were 81.1 kJ·mol-1 without CO2,and 87.1 kJ·mol-1 with CO2 initial pressure at 0.2 MPa,which showed no significant difference.The main by-product was confirmed to be 2,3-dimethyl-3-butadiene by GC/MS and the possible reaction mechanism was proposed.
