烯丙醇化合物的不对称环氧化

本文报道了三个脂肪族烯丙醇化合物(1-3)的不对称环氧化反应。由反式烯丙醇2得到的反式烯丙醇环氧化合物2a的对映体过量大于由顺式烯丙醇1得到的环氧化合物1a的对映体过量。叔羟基二取代烯丙醇3经不对称环氧化生成的3a,其对映体过量只有4%。     

Iridium‐Catalyzed Intermolecular Asymmetric Dearomatization of β‐Naphthols with Allyl Alcohols or Allyl Ethers

An Ir‐catalyzed intermolecular asymmetric dearomatization reaction of β‐naphthols with allyl alcohols or allyl ethers was developed. When an iridium catalyst generated from [Ir(COD)Cl]₂ (COD=cyclooctadiene) and a chiral P/olefin ligand is employed, highly functionalized β‐naphthalenone compounds bearing an all‐carbon‐substituted quaternary chiral center were obtained in up to 92 % yield and 98 % ee . The direct utilization of allyl alcohols as electrophiles represents an improvement from the viewpoint of atom economy. Allyl ethers were found to undergo asymmetric allylic substitution reaction under Ir catalysis for the first time. The diverse transformations of the dearomatized product to various motifs render this method attractive.     

Molecular versus Silica-Supported Iridium Water Oxidation Catalysts

A stringent comparison between two pairs of molecular/immobilized water oxidation catalysts ([Cp^*Ir(Me-pica)Cl], 1 , versus 1_SiO₂ , Me-pica=κ²-N-methyl-picolinamide; [Cp^*Ir(pysa)NO₃], 2 , versus 2_SiO₂ , pysa=κ²-pyridine-2-sulfonamide]) reveals distinctive catalytic trends. While the molecular compound 1 exhibits a substantial higher activity than the analogous immobilized system 1_SiO₂ , under all the experimental conditions explored, the contrary is found with 2 that is far less active than its immobilized counterpart 2_SiO₂ . This is explained by the unique tendency of 2 to form dimeric complexes [Cp^*Ir-(κ²-μ₂-Hpysa)(κ²-μ₂-pysa)IrCp^*], 2 a , in phosphate buffered solution at pH 7, and [Cp^*Ir-(κ²-μ₂-Hpysa)₂IrCp^*], 2 b , in water. 2 a and 2 b have been completely characterized in solution by multinuclear and multidimensional NMR spectroscopy. They have been also isolated as single crystals and their structure in solid state determined by X-Ray diffractometry. 2 a and 2 b appear to be off-cycle species, whose formation is detrimental for water oxidation activity, as indicated by the observation of a long induction period when 2 a is used as catalytic precursor. In addition, TOF versus ΔE (E−E⁰=−RT/nF ln([IO₄⁻]/[IO₃⁻]) trends for the first two runs do not overlap for catalyst 2 and TOF_max is remarkably higher in the second run upon the addition of fresh NaIO₄. In the immobilized system 2_SiO₂ the detrimental associative processes are likely inhibited leading to an activity higher than that of 2 .     

Precursor-Support Interactions in Silica-Supported Manganese Oxide Catalysts

Summary. Catalyst materials investigated in this study were obtained by calcination of impregnated silica with Mn(CH₃COO)₂·4H₂O and MnC₂O₄·2H₂O, so as to yield 10wt% Mn/SiO₂. The precursor compounds as well as pure and impregnated silica support were calcined at 600 and 1000°C in a static air atmosphere for 5h. Structural characteristics of the catalysts thus obtained were investigated by DTA, TG, XRD, IR and DRS. N₂ adsorption at –195°C was used for the assessment of surface texture of the test materials. Results of structural characterisation of catalysts obtained by calcination of manganese acetate-impregnated silica at 1000°C indicated the presence of strong silica-precursor interactions. Species of manganese silicates were detectable. Moreover, the decomposition of manganese acetate enhanced the transformation of amorphous silica into well crystallised -quartz. In contrast, Mn₂O₃, Mn₃O₄, and minor proportions of MnO were detected in the catalysts derived from the manganese oxalate-impregnated silica. This has been ascribed to much weaker precursor/support interactions in the oxalate-impregnated silica than the acetate-impregnated one.     

Iodoalkoxylation of Cyclohexene with Allyl and Propargyl Alcohols

Russian Journal of Organic Chemistry -     

Liquid-Phase Selective Oxidation of Propane on Silica-Supported Nafion Catalysts

The liquid-phase partial oxidation of propane in the presence of the Fen+/H2O2 Fenton system at 70℃ and 1.4 atm on silica supported Nafion catalysts has been investigated. The reaction proceeds via a radical reaction path the efficiency of which is improved by silica-supported Nafion catalysts. Because of the direct relationship between reaction rate and concentration of sulphonic acid sites of Nafion catalysts, it is inferred that the active phase enahnces the kinetics of propane conversion by promoting the rate of active radicals generation.     

Liquid-Phase Selective Oxidation of Propane on Silica-Supported Nafion Catalysts

The liquid-phase partial oxidation of propane in the presence of the Fen+/H2O2 Fenton system at 70℃ and 1.4 atm on silica supported Nafion catalysts has been investigated. The reaction proceeds via a radical reaction path the efficiency of which is improved by silica-supported Nafion catalysts. Because of the direct relationship between reaction rate and concentration of sulphonic acid sites of Nafion catalysts, it is inferred that the active phase enahnces the kinetics of propane conversion by promoting the rate of active radicals generation.     

Improved Catalysts for the Iridium‐Catalyzed Asymmetric Isomerization of Primary Allylic Alcohols Based on Charton Analysis

An improved generation of chiral cationic iridium catalysts for the asymmetric isomerization of primary allylic alcohols is disclosed. The design of these air‐stable complexes relied on the preliminary mechanistic information available, and on Charton analyses using two preceding generations of iridium catalysts developed for this highly challenging transformation. Sterically unbiased chiral aldehydes that were not accessible previously have been obtained with high levels of enantioselectivity, thus validating the initial hypothesis regarding the selected ligand‐design elements. A rationale for the high enantioselectivities achieved in most cases is also presented.     

新型固载化的匀相催化剂

多相催化和匀相催化是催化领域里的两大类型,两者相比,匀相催化剂具有高活性、高选择性、反应条件温和等优点.然而,催化剂和产品分离难的问题,使匀相催化剂的应用受到很大的限制.20世纪60年代末,人们就开始将过渡金属配合物以化学键合形式锚定在载体上,制备负载型催化剂.这种固载化催化剂介于匀相催化剂与多相催化剂之间,它既具有匀相催化的特性,又具有多相催化产品与催化剂易分离的优点.而且,对这类催化剂进行研究,有可能在分子水平上研制出反应性能优异的催化剂,并对其催化作用机理有更进一步的认识.固载化匀相催化剂是一种很有前途的…     

基于肽的不对称催化剂

综述了肽作为有机催化剂以及金属配体在不对称催化反应中的应用, 概括了人们所发现的各种肽催化剂的结构、催化活性以及机理, 并对发现这些肽的过程中所采用的研究方法做了具体的介绍.     

Asymmetric Organocatalytic Epoxidations: Reactions,Scope, Mechanisms,and Applications

Chiral epoxides serve as versatile building blocks in the synthesis of complex organic frameworks. The high strain imposed by the three‐membered ring system makes epoxides prone to a variety of nucleophilic ring‐opening reactions. Since the development of the Sharpless epoxidation, there have been many important contributions and advances in this area. With the rapid development of the field of asymmetric organocatalysis, a wide range of organocatalysts is now able to catalyze the epoxidation of broad class of unsaturated carbonyl compounds. In this Minireview, recent progress in the development of organocatalytic asymmetric epoxidation methods, the proposed mechanisms of these reactions and their applications as intermediates is reported.     

醇在钒基催化剂上的氧化

以过氧化叔丁醇作为氧化剂,研究了醇类(苯甲醇、1-苯基乙醇和环己醇)在钒基催化剂上的氧化反应.制备了含苯磷二酚配体或吡嗪-2-羧酸酯配体的钒配合物,并运用傅里叶变换红外光谱、核磁共振谱、紫外-可见光谱及元素分析对其进行了表征.考察了溶剂对该类反应的影响.发现在甲苯溶剂中进行氧化反应时,苯甲醇被氧化成苯甲醛而不会被深度氧化为苯甲酸;而在乙腈溶剂中,苯甲醛和苯甲酸均有生成.此外,对不同钒磷氧化物的催化活性进行了比较,结果表明,在乙腈溶剂中的产品收率比在甲苯溶剂中高.     

Convenient Asymmetric Syntheses of anti-beta-Amino Alcohols

Condensation of allylborane reagents 9 and 12 with aldehydes gave anti-3-[(diphenylmethylene)amino]-1-alken-4-ols 10 and 13 with high relative and absolute stereocontrol. Subsequent deprotection gave the corresponding free anti-3-amino-1-alken-4-ols 11 and 14. Alternatively, reaction of imines 13a, 13f, and 13g with trifluoromethanesulfonic anhydride and acidic methanol gave, via rearrangement, double inversion, and hydrolysis, the isomeric anti-4-amino-1-alken-3-ols 22, 38a, and 38b in good yield. The stereochemistry of the rearrangement products has been established by a single crystal X-ray study of compound 37 and by chemical correlation.     

Silica-Supported 4-OH-TEMPO/NOx: A Novel and Efficient Catalyst for Aerobic Oxidation of Alcohols

Silica-supported 4-OH-2,2,6,6-tetramethylpiperidyl-1-oxy/NO_x (4-OH-TEMPO was immobilized on the surface of silica using the sol-gel method, and then it adsorbed NO_x), as a heterogeneous catalyst, has exhibited good catalytic performance in alcohol oxidation. A broad range of alcohols were oxidized to their corresponding aldehydes or ketones with more than 99% selectivity and 99% conversion rate by such a catalyst system at room temperature in air. NO_x not only acted as an electron bridge between O₂ and 4-OH-TEMPO but also were conducive to the formation of the aldehydes as active component. A possible mechanism for oxidation of alcohols promoted by silica-supported 4-OH-TEMPO/NO_x was supposed.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

制备高碳醇Cu-Fe系催化剂的TPR研究

利用ＴＰＲ研究了Ｃｕ－Ｆｅ系催化剂的还原行为和各组分间的相互作用．指出Ｃｕ－Ｆｅ系催化剂的活性与其还原行为密切相关．由共沉淀法制备的Ｃｕ－Ｆｅ系催化剂，各组分间的相互作用影响催化剂的活性．并用Ｃｏａｔｓ－Ｒｅｄｆｅｒｎ方法，求得了Ｃｕ－Ｆｅ系催化剂还原的动力学参数．     

Study on Sharpless Kinetic Resol Ution of Racemic Allyl Propargyl Alcohols

A kinetic resolution of racemic allyl propargyl alcohols by enantioselective epoxidation is described.     

Proline‐Modified Porphyrin Catalysts for Enantioselective Epoxidations: Design,Synthesis, and Reactivity

The syntheses of various strapped and ‘picket‐fence’ chiral porphyrins are described, and their reactivities towards the enantioselective epoxidation of alkenes are reported. Four L ‐proline residues provide the chirality for the various meso‐substituted catalysts, which differ by either the spatial arrangement of the stereogenic centers or the nature and length of the straps. The resulting bridged structures possess four amide linkages in each strap, leading to highly rigid molecules with well‐defined geometries whereas the strapped Fe catalysts gave rise to only moderate enantioselectivities, the C₂‐symmetrical ones being superior to the D₂‐symmetrical compounds. The D₂‐symmetrical ‘picket‐fence’ porphyrins were as selective as their strapped counterparts.