利用Sharpless不对称双羟基化反应制备光学活性的偶姻类化合物

以相应的酮为起始原料,通过烯醇硅醚的中间体,利用Sharpless不对称双羟基化反应制备了5个光学活性的偶姻化合物。4-庚酮、5-壬酮、2,6-二甲基-4-庚酮、5-甲基-3-己酮和4-苯基-2-丁酮在不同碱的作用下与三甲基氯硅烷或三甲基碘硅烷反应得到动力学控制或热力学稳定的烯醇硅醚后,再进行Sharpless不对称双羟基化反应,除5-甲基-3-己酮的烯醇硅醚外,其他烯醇硅醚用AD-mix-α氧化得到S构型的偶姻产物,对映体过量值(ee值)在62%以上,用AD-mix-β氧化得到R构型的偶姻产物,ee值在75%以上。5-甲基-3-己酮的烯醇硅醚分别用AD-mix-α和AD-mix-β氧化都得到R构型的2-羟基-5-甲基-3-己酮,前者ee值只有16%,后者ee值为76%;用D-果糖和L-果糖衍生的史一安催化剂和过硫酸氢钾氧化,则分别得到R构型和S构型产物,ee值分别为75%和73%。     

Catalytic Asymmetric Dihydroxylation of Aliphatic Olefins with Reusable Resin‐Osmium Tetroxide

Asymmetric dihydroxylation of aliphatic olefins to chiral diols with good yields and ees by a heterogeneous Resin‐OsO₄ catalyst using ferricyanide as cooxidant is disclosed for the first time. The catalyst was recovered quantitatively by simple filtration and reused for several times without significant loss of activity.     

MCM-41 Anchored Cinchona Alkaloid for Catalytic Asymmetric Dihydroxylation of Olefins: A Clean Protocol for Chiral Diols Using Molecular Oxygen

MCM-41 anchored 1,4-bis(9-O-quininyl)phthalazine (MCM-(QN)₂PHAL)-OsO₄, is prepared for the first time and used in the heterogeneous asymmetric dihydroxylation of olefins to afford diols with good to excellent enantiomeric excesses in the presence of N-methylmorpholine N-oxide, K₃Fe(CN)₆ or molecular oxygen as cooxidants.     

A Novel Chemoentrapment Approach for Supportless Recycling of a Catalyst: Catalytic Asymmetric Dihydroxylation

A simple method of recycling a metal catalyst through chemoentrapment in an aqueous layer using ethyl vinyl ether has been developed. Using this new methodology, a highly efficient, filtration‐free recycling of osmium for catalytic asymmetric dihydroxylation was accomplished. By means of the formation of a water‐soluble OsO₄²⁻ using EVE, AD reactions of mono‐ and disubstituted olefins with 1 mol % of OsO₄ proceeded for up to 9 cycles without any loss of yields and enantioselectivities.     

Microencapsulated Osmium Tetroxide‐Catalyzed Asymmetric Dihydroxylation of Olefins in Water without Using Organic Cosolvents

The asymmetric dihydroxylation of olefin using phenoxyethoxymethyl‐polystyrene (PEM)‐based microencapsulated osmium tetroxide (PEM‐MC OsO₄) proceeded smoothly in water as the sole solvent. The catalyst was recovered quantitatively by simple filtration and reused several times without loss of activity.     

Silica Gel‐Supported Cinchona Alkaloid‐OsO4 Complex for Catalytic Heterogeneous Asymmetric Dihydroxylation of Olefins by H2O2 using a Titanium Silicalite‐Based Coupled Catalytic System

A triple catalytic system designed for asymmetric dihydroxylation of olefins, composed of NMM and two divergent heterogeneous catalysts, titanium silicalite and silica gel‐supported 1,4‐bis(9‐O‐dihydroquinidinyl)phthalazine [SGS‐(DHQD)₂PHAL)]‐OsO₄ complex relays the transport of two electrons from olefin to H₂O₂ used as a terminal oxidant to provide chiral diols with good yields and high enantiomeric excesses in a single pot.     

A Novel Microencapsulated Osmium Catalyst Using Cross‐Linked Polystyrene as an Efficient Catalyst for Asymmetric Dihydroxylation of Olefins in Water

A novel microencapsulated osmium catalyst (PSresin‐MC Os) was developed using cross‐linked polystyrene. The concept of this method may go beyond that of microencapsulation. The catalyst was successfully used in asymmetric dihydroxylation in water, and it was recovered quantitatively by simple filtration and reused several times without loss of activity. The shape of the catalyst was maintained even after several uses. Moreover, no leaching of the Os component was detected.     

Polymer Enzyme Conjugates as Chiral Ligands for Sharpless Dihydroxylation of Alkenes in Organic Solvents

Conjugates of enzymes and poly(2‐methyloxazoline) were used as organosoluble amphiphilic polymer nanocontainers for dissolving osmate, thereby converting the enzymes into organosoluble artificial metalloenzymes. These were shown to catalyze the dihydroxylation of different alkenes with high enantioselectivity. The highest selectivities, found for osmate complexed with laccase polymer–enzyme conjugates (PECs), even exceed those of classical Sharpless catalysts.     

Achiral Dihydroxylation of Olefins by Osmate (OsO42−) Stabilised on Nanocrystalline Magnesium Oxide

A recoverable and reusable new heterogeneous AP‐Mg‐OsO₄ catalyst was designed and developed for the first time via a counterionic stabilisation of OsO₄²⁻ with Mg²⁺ present on the corner or edge of nanocrystalline MgO. AP‐Mg‐OsO₄ catalysed the dihydroxylation of olefins to afford diols with excellent yields in the presence of N‐methylmorpholine N‐oxide for the first time. The absence of osmium and no progress of the dihydroxylation reaction with the filtrate samples withdrawn periodically during the reaction rule out the leaching of osmium unambiguously and provide evidence for the heterogeneity of the reaction. Identification of surface intermediate species by XPS and TGA‐DTA‐mass thermography gives an insight into the mechanism of the dihydroxylation reaction.     

Efficient Osmium/Rhenium‐Catalyzed Dihydroxylation of Olefins with Hydrogen Peroxide under Acidic Conditions

Simple addition of citric acid confers great stability to the catalytically active osmium and rhenium species involved in a triple catalytic system utilizing aqueous hydrogen peroxide as the terminal oxidant. The resulting system is capable of dihydroxylating traditionally resistant olefins in high yields.     

Brønsted Acid‐Catalyzed Dihydroxylation of Olefins in Aqueous Medium

The trans‐dihydroxylation of olefins occurs efficiently by aqueous hydrogen peroxide catalyzed by p‐toluenesulfonic acid at 50 °C, allowing the catalyst reuse and an outstanding substrate functional group tolerance such as tert‐butoxycarbonylamino (BocNH), benzyloxycarbonylamino (CbzNH), benzyloxy (OBn), tosyloxy (OTs), hindered ketal, (2‐trimethylsilyl)ethoxymethoxy (OSEM), benzylamino (NBz), benzyloxy (OBz) and free amino acid.     

New Mono‐Quarternized Bis‐Cinchona Alkaloid Ligands for Asymmetric Dihydroxylation of Olefins in Aqueous Medium: Unprecedented High Enantioselectivity and Recyclability

New mono‐quaternized allyl bromide salts of bis‐Cinchona alkaloid ligands, [(QD)₂PHAL‐Allyl]Br and [(QN)₂PHAL‐Allyl]Br, have been synthesized which can be converted into their highly water‐soluble multihydroxylated derivatives under asymmetric dihydroxylation (AD) conditions and, thus, easily recovered by a simple extraction method after reaction and reused. These mono‐quaternized ligands exhibited superior catalytic efficiency to their neutral counterparts such as (DHQD)₂PHAL and (DHQ)₂PHAL for the AD reactions of mono‐ and disubstituted styrenes under Upjohn conditions. Merely 0.1 mol % of osmium was enough to complete the reactions of mono‐ and disubstituted styrenes and, moreover, these ligands showed the highest enantioselectivities (e.g., for styrene, 97 % ee with [(QD)₂PHAL‐Allyl]Br) among those ever achieved under Upjohn conditions.     

Osmium‐Catalyzed Olefin Dihydroxylation and Aminohydroxylation in the Second Catalytic Cycle

Two catalytic cycles operate in the osmium‐catalyzed olefin dihydroxylation and aminohydroxylation. Slow hydrolysis of the Os(VI) monoglycolate (or monoazaglycolate in aminohydroxylation) intermediate often results in the addition of another molecule of olefin thereby shunting the catalysis into the second catalytic cycle. As a result, both enantio‐ and chemoselectivity are reduced. A series of new chelating ligands were devised, which force the catalysis into the second cycle while maintaining enantiocontrol in the olefin addition step. Excellent catalytic turnover and moderate to good enantioselectivity were achieved.     

Tuning the Peri Effect for Enantioselectivity: Asymmetric Hydrogenation of Unfunctionalized Olefins with the BIPI Ligands

The modular nature of the BIPI ligands allows for systematic optimization of each ligand region. The development of ligands optimized for asymmetric hydrogenation of the challenging unfunctionalized olefin substrate class is described. The naphthyl peri position, C‐8, has been identified as a critical stereocontrol element in the design of these ligands. Highly enantioselective ligands suitable for hydrogenation of tri‐ and tetrasubstituted olefins are detailed.     

基于纳滤膜的增白剂清洁生产工艺

采用纳滤膜分离技术替代原有的酸析工艺对增白剂合成液进行脱盐和浓缩,以提高产品质量,减少污染物排放。小试实验表明,纳滤膜对增白剂的平均截留率98 9%,对盐基本没有截留效果。清洁生产实验表明,增白剂溶液经过脱盐浓缩后,增白剂质量分数从5 0%提高到25 0%,无机盐质量分数从2 0%降低到0 05%;膜分离产品与酸析产品相比,白度和强度均有所提高,而在盐度指标上有了大幅度提高,产品整体性能得到提升;膜分离工艺所排污染物总量只有原工艺的1/4,新工艺减污效果明显;纳滤膜在使用过程中,膜通量随时间的延长而变小,这主要是凝胶层造成的,可通过酸洗使其恢复。     

Chiral 1-Phosphabarrelene-Pyridines as Suitable Ligands for the Rh/Ir-Catalyzed Asymmetric Hydrogenation of Olefins

Herein, we report the synthesis of chiral phosphabarrelene-pyridine ligands. Their synthesis benefit from modified reaction conditions to overcome the low yields normally associated with the [4+2] cycloaddition reaction of phosphinines with hexafluoro-2-butyne, which is a key to install the P-stereocenter in the phosphabarrelene. Their potential as chelating ligands in asymmetric catalysis was assessed in the Rh- and Ir-catalyzed hydrogenation of cyclic β-enamides and β-dehydroamino acid derivatives. The catalytic system containing a tert-butyl substituent at the ortho position of the phosphabarrelene moiety successfully hydrogenates a range of cyclic β-enamides (ee's between 92% to 94%) and β-dehydroamino acid derivatives (ee's between 93% to 95%). Moreover, the reactions can be carried out in the environmentally friendly 1,2-propylene carbonate as solvent with no loss of enantioselectivity. Mechanistic studies with the Rh/P,N catalytic systems agree with the Landis-Halpern mechanism and explain the influence of the substituent at the phosphabarrelene on enantioselectivity. Finally, the hydrogenation reactions can be carried out at large scale maintaining high enantioselectivities.     

Catalytic Asymmetric Epoxidation of Unfunctionalized Olefins by Supported Cu(II)-Amino Acid Complexes

Polymer-supported Cu(II) complexes with L-phenyl alanine and L-valine were used as chiral catalysts for asymmetric epoxidation of nonfunctionalized straight-chain terminal olefins viz. 1-octene, 1-hexene, 2-methyl-1-pentene and 4-methyl-1-pentene using m-chloroperbenzoic acid (m-CPBA) as oxidant giving high conversions and selectivity. Enantiomeric yields, though moderate, are comparable with the best-reported ees using homogeneous catalysts. All catalysts displayed good recycling efficiency. Variations in percent ee have been discussed on the basis of the structural geometry of the supported catalysts and the trajectory of the olefin approach to the active oxo-intermediate.     

Towards a Greener Epoxidation Method: Use of Water‐Surfactant Media and Catalyst Recycling in the Platinum‐Catalyzed Asymmetric Epoxidation of Terminal Alkenes with Hydrogen Peroxide

Remarkable improvements in enantioselectivity as well as recycle were observed in the catalytic asymmetric epoxidation of terminal alkenes with a chiral, electron‐poor platinum(II ) catalyst with hydrogen peroxide as terminal oxidant in water‐surfactant media.     

Separation of Liquiritin from Glycyrrhizic Acid in Licorice Root Extract by Nanofiltration Membrane

The aim of this work was to study the separation of liquiritin (LQ) from glycyrrhizic acid (GA), in licorice aqueous solutions using nanofiltration (NRT-7450) membrane. The LQ and GA components are the main active ingredients of licorice root extract with various pharmacological effects, The effects of transmembrane pressure, feed temperature, feed pH, and cross-flow velocity on permeate flux and recovery were determined. A lab scale cross-flow set up using flat-sheet configuration membrane was employed for all experiments. SEM micrographs showed the changes in the fouled surface during operating time. The applied transmembrane pressure, feed temperature, feed pH, and cross-flow velocity were varied from 4 to 10 bars, 30 to 40°C, 3 to 9, and 0.8 to 3.1 m s^?1 respectively. The obtained recoveries for GA and LQ varied between 0.65 to 1.86% and 16.89 to 41.65%, respectively. The optimum operating conditions for separation LQ from GA in licorice aqueous solutions using NRT-7450 nanofiltration membrane were 1.8 m s^?1cross-flow velocity, 8 bars transmembrane pressure, 40°C of feed temperature and pH 7.