Transition-Metal-Catalyzed Highly Regio- and Stereoselective Co-Polymerization of Dialkynylbenzene with Benzenedithiol Leading to Poly（Phenylene Vinylene Sulfide）

Co-polymerization of dialkynylbenzene with benzenedithiol proceeds regio- and stereoselectively in the presence of transition metal catalysts, affording the corresponding poly（phenylene vinylene sulfide） in good yield. In the presence of palladium acetate as catalyst, Markovnikov addition takes place selectively, whereas chlorotris（triphenylphosphine）rhodium-catalyzed reaction affords anti-Markovnikov adduct with excellent regio- and stereoselectivity.     

Modification effect of metal cations on the stereoselective hydrogenation of 2,3-butanedione

The modification of some metal cations to alumina-supported Pt nanoclusters induces 100% selectivity for meso-2,3-butanediol in the stereoselective hydrogenation of 2,3-butanedione.     

Stereoselective acylation of Dl-menthol in organic solvents by an immobilized lipase from Pseudomonas cepacia with vinyl propionate

An effective lipase-catalyzed stereoselective transesterification of (±)-menthol in organic solvent with vinyl propionate as acylating agent is described. Immobilization by adsorption and the presence of molecular sieves improved the formation of (±)-menthyl propionate by lipase (PS-30) from Pseudomonas cepacia. The reaction time course, mole ratio of substrates, temperature, amount of enzyme, as well as the effect of various organic solvents, were examined for their influence on the enzymatic stereoselective formation of (−)-menthyl propionate. Among the parameters studied, the stereospecificity toward (−)-menthol decreased significantly as temperature increased but the yields of both enantiomers increased. Organic solvents with log P (partition coefficient) values above 3.5 gave higher yield and stereoselectivity than solvents with lower log P values.     

粉唑醇在草莓生长和加工过程中对映体选择性降解行为规律

为研究手性农药粉唑醇在草莓生长及草莓酒加工过程中的选择性降解行为,对草莓进行田间施药,并将草莓模拟家庭酿酒方式加工。样品采用超高效合相色谱-串联质谱进行手性拆分并检测。结果表明,在草莓生长中两个对映体没有明显的选择性降解行为,（－）-R-粉唑醇在草莓上的半衰期为13.80?d,（＋）-S-粉唑醇在草莓上的半衰期为13.60?d。而在草莓酒发酵过程中,统计学分析显示存在明显的选择性降解行为（P＜0.05）,（＋）-S-粉唑醇优先降解。清洗处理组（－）-R-粉唑醇在草莓酒中的半衰期为38.06?d,（＋）-S-粉唑醇的半衰期为29.90?d。未清洗处理组（－）-R-粉唑醇在草莓酒发酵中的半衰期为29.31?d,（＋）-S-粉唑醇半衰期为22.14?d。     

Microbial synthesis of chiral intermediates for β-3-receptor agonists

Chiral intermediates were prepared by biocatalytic processes for the chemical synthesis of β-3-receptor agonists. These include: (i) the microbial reduction of 4-benzyloxy-3-methanesulfonylamino-2′-bromoacetophenone 1 to the corresponding (R)-alcohol 2 by Spingomonas paucimobilis SC 16113. In the biotransformation process, a reaction yield of >85% and an optical purity of 99.5% were obtained for the desired (R)-alcohol 2; (ii) the enzymatic resolution of racemic α-methyl phenylalanine amide, 3, and α-methyl-4-hydroxy-phenylalanine amide, 5, by amidase from Mycobacterium neoaurum ATCC 25795 to prepare the corresponding (S)-amino acids 4 and 6. Reaction yields of 49.9 and 49 M% (theoretical maximum yield 50 M%) and optical purities of 99 and 94% were obtained for the desired (S)-amino acids 4 and 6, respectively; (iii) the asymmetric hydrolysis of methyl-(4-methoxyphenyl)-propanedioic acid, ethyl diester, 7, to the corresponding (S)-monoester 8 by pig liver esterase. A reaction yield of 96 M% and an optical purity of 96% were obtained for (S)-monoester 8 when reactions were carried out in a biphasic system containing 10% ethanol at 10°C.     

Synthesis of poly(methylphenylsiloxane) rich in syndiotacticity by Rh‐catalysed stereoselective cross‐dehydrocoupling polymerization of optically active 1,3‐dimethyl‐1,3‐diphenyldisiloxane derivatives

Cross‐dehydrocoupling reactions of (R)‐methyl(1‐naphthyl)phenylsilane (>99%ee) with (S)‐methyl(1‐naphthyl)phenylsilanol (>99% ee) proceeded with 82–99% retention of configuration of chiral silicon centres in the presence of various Rh‐catalysts. Cross‐dehydrocoupling polymerization of 1,3‐dimethyl‐1,3‐diphenyl‐1,3‐disiloxanediol with 1,3‐dihydro‐1,3‐dimethyl‐1,3‐diphenyl‐1,3‐disiloxane gave poly(methylphenylsiloxane) of moderate molecular weight in toluene at 60 °C in the presence of [RhCl(cod)]₂ (5.0 mol%) and triethylamine (1.0 equivalent). Assignment of the triad signals of the resulting polymer was made by ¹H NMR spectroscopy of the methyl proton (I = 0.04, H = 0.09 and S = 0.14 ppm) and ¹³C NMR spectroscopy of the ipso carbon of the phenyl group (S = 136.7, H = 136.9, and I = 137.1 ppm). Although the reaction of optically pure (S,S)‐1,3‐dimethyl‐1,3‐diphenyl‐1,3‐disiloxanediol with 1,3‐dihydro‐1,3‐dimethyl‐1,3‐diphenyl‐1,3‐disiloxane [(S,S):(S,R):(R,R)] = 84:16:0] gave a poly(methylphenylsiloxane) of rather low molecular weight, its triad tacticity was found to be rich in syndiotacticity (S:H:I = 60:32:8) by ¹³C NMR spectroscopy. © 2001 Society of Chemical Industry     

Stereoselective Epoxidation of Alkenes with Hydrogen Peroxide using a Bipyrrolidine‐Based Family of Manganese Complexes

Novel manganese complexes containing N₄‐tetradentate ligands derived from chiral bipyrrolidinediamines catalyze the stereoselective epoxidation of a wide array of alkenes using low catalyst loadings (0.1 mol%) and hydrogen peroxide (1.2 equiv.) as terminal oxidant. This family of catalysts affords good to excellent yields (80–100%) and moderate to good ees (40–73%) in short reaction times (30 min) making efficient use of hydrogen peroxide.