Carbenium ion trapping using sulfonamides: an acid-catalysed synthesis of pyrrolidines by intramolecular hydroamination

Cyclisations of homoallylic sulfonamides proceed smoothly via carbenium ion generation using trifluoromethanesulfonic (triflic) acid, the ease of cyclisation being directly related to the ion stability to give good to excellent yields of the corresponding pyrrolidines. Both toluene- and nitrophenyl-sulfonyl groups are suitable for all substrates tested whereas the corresponding carbamates are only useful in cases of tertiary and highly stabilised carbenium ions. Polyene-derived sulfonamides can also be cyclised to the corresponding polycyclic systems in remarkably high yields, in reactions reminiscent of related cascades encountered in terpene biosynthesis.     

Sulfonylation of arenes with sulfonamides

In the presence of triflic anhydride, sulfonylation of arenes with sulfonamides proceeded smoothly in Cl₂CHCHCl₂ at 80-140 °C, which gave rise to the desired products in good to excellent yields.     

埃洛石表面修饰并负载salen钼高效催化烯烃环氧化反应

采用温和的化学表面改性和自组装方法成功制备了埃洛石纳米管负载salen钼(HNTs-SL-Mo)催化剂,运用透射电镜、X射线衍射、红外光谱、诱导偶合等离子体谱和X射线光电子能谱表征了催化剂的形态、大小和分散性等性质。结果证明了salen结构的存在和埃洛石配位钼催化剂的成功制备。制备的催化剂在各种烯烃的环氧化反应中均有很好的活性,且活性高于均相催化剂。对比实验表明,在固定MoO(O2)2(DMF)2时, salen结构发挥了重要作用,不能用N原子作为单一配体来代替。本文还推测了钼和salen配体可能的连接方式和该催化剂催化烯烃环氧化反应的机理。该催化剂在重复使用8次后其活性未见明显下降,表现出优异的重复使用性能。由于埃洛石是一种廉价易得的材料,因此它可为设计效果独特的催化剂提供一个选择。     

埃洛石表面修饰并负载salen钼高效催化烯烃环氧化反应

采用温和的化学表面改性和自组装方法成功制备了埃洛石纳米管负载salen钼(HNTs-SL-Mo)催化剂,运用透射电镜、X射线衍射、红外光谱、诱导偶合等离子体谱和X射线光电子能谱表征了催化剂的形态、大小和分散性等性质。结果证明了salen结构的存在和埃洛石配位钼催化剂的成功制备。制备的催化剂在各种烯烃的环氧化反应中均有很好的活性,且活性高于均相催化剂。对比实验表明,在固定MoO(O2)2(DMF)2时, salen结构发挥了重要作用,不能用N原子作为单一配体来代替。本文还推测了钼和salen配体可能的连接方式和该催化剂催化烯烃环氧化反应的机理。该催化剂在重复使用8次后其活性未见明显下降,表现出优异的重复使用性能。由于埃洛石是一种廉价易得的材料,因此它可为设计效果独特的催化剂提供一个选择。     

Synthesis of 1,6-anhydro sugars catalyzed by silica supported perchloric acid

A new and efficient method for the preparation of 1,6-anhydro sugars using silica supported perchloric acid as a catalyst is described. The catalyst is heterogeneous and 1,6-anhydro sugars could be formed within a few minutes with good yields.     

On the role of triflic acid in the metal triflate-catalysed acylation of alcohols

The acylation of alcohols by anhydrides, catalysed by a wide range of metal triflates, is a powerful and mild method for the preparation of a variety of esters. Mechanistic insights demonstrate that triflic acid is generated under these reaction conditions and that, at least, two competing catalytic cycles are operating at the same time: a rapid one involving triflic acid and a slower one involving the metal triflate.     

Silica supported Ru(salophen)Cl: An efficient and robust heterogeneous catalyst for epoxidation of alkenes with sodium periodate

In the present work, heterogenization of Ru(salophen)Cl via its axial ligation to silica-bound imidazole, SiIm, is reported. The heterogeneous catalyst, [Ru(salophen)Cl–SiIm], was characterized by elemental analysis, SEM, TEM, FT-IR and diffuse reflectance UV–Vis spectroscopic techniques. The catalyst, which is not soluble in water and common organic solvents, was used for efficient epoxidation of cyclic and linear alkenes with NaIO₄ under agitation with magnetic stirring. This new heterogenized catalyst is of high stability and reusability in the oxidation reactions. The effect of reaction parameters such as solvent and oxidant in the epoxidation of cis-cyclooctene were also investigated.     

Heptadecafluorooctanesulfonic acid (C8F17SO3H) catalyzed intramolecular hydroamination of olefinic sulfonamides in fluorous biphase system (FBS)

A practical, efficient, and environmentally benign intramolecular hydroamination of olefinic sulfonamides was carried out in fluorous biphase system (FBS) using commercially available heptadecafluorooctanesulfonic acid (C₈F₁₇SO₃H) as a catalyst and perfluorodecaline (C₁₀F₁₈, cis- and trans- mixture) as a fluorous solvent to produce the corresponding cyclic products in good yields. The Brønsted acid of C₈F₁₇SO₃H is easily recovered and recycled at least five times.     

Mild, selective deprotection of PMB ethers with triflic acid/1,3-dimethoxybenzene

An efficient method for the cleavage of the p-methoxybenzyl protecting group of several alcohols in the presence of 0.5 equiv of trifluoromethanesulfonic acid and 1,3-dimethoxybenzene in dichloromethane at room temperature is described.     

Catalytic hydrogenation by recyclable supported Pd(II)-amino acid complex

L-phenyl alanine was anchored to P(S-DVB) resin and its complex with PdCl₂ was prepared. The newly synthesized catalyst was found to be a versatile and recyclable catalyst for the hydrogenation of 1-octene and acetophenone. This chiral catalyst induced moderate enantioselectivity during the asymmetric reduction of acetophenone. This revised version was published online in June 2006 with corrections to the Cover Date.     

Efficient intramolecular hydroamination of aminoalkynes catalyzed by a zirconium(IV) complex

The neutral zirconium(IV) bis(thiophosphinic amidate) complex was demonstrated to be an effective precatalyst for 5-exo-, 6-exo-, and 7-exo-dig intramolecular hydroamination of aminoalkynes, producing the cyclic imines in excellent yields (92-98%).     

Hydroarylation of alkynes and alkenes through alumina-sulfuric acid catalyzed regioselective CC bond formation

A highly atom-efficient synthetic protocol for hydroarylation of terminal-aryl alkynes and styrene through the regioselective CC bond formation via the electrophilic addition of naphthols and substituted phenols has been developed using alumina-sulfuric acid as a heterogeneous supported solid acid catalyst. This methodology shows excellent regioselectivity and affords the desired product in good to excellent yield. The heterogeneous catalyst can also be recycled efficiently without much loss of activity.     

Intramolecular hydroamination of 6-aminohex-1-yne catalyzed by Lewis acidic rhenium(I) carbonyl complexes

With the aim to determine the effect of Lewis acidity of rhenium(I) carbonyl complexes on their catalytic properties, and to develop more efficient catalysts based on Re(I) carbonyl systems, a series of rhenium(I) carbonyl triflate complexes with various degrees of Lewis acidity was investigated. Pyridine-substituted bromo tricarbonyl rhenium(I) complexes of the type fac-[ReBr(CO)₃L₂] (L = py-Cl, py, py-Me and py-NMe₂) were synthesized from [ReBr(CO)₅] using trimethylamine N-oxide (TMNO) as decarbonylating agent. The complexes [ReBr(CO)₅] and fac-[ReBr(CO)₃L₂] were then reacted with silver triflate to yield the complexes [Re(CF₃SO₃)(CO)₅] and fac-[Re(CF₃SO₃)(CO)₃L₂]. The synthesis and characterization of these complexes and their application in the catalysis of the cyclization of 6-aminohex-1-yne are discussed. The crystal structure of [Re(CF₃SO₃)(CO)₃(py)₂] is also presented.     

Asymmetric hydroamination/cyclization catalyzed by group 4 metal complexes with chiral biaryl-based ligands

Group 4 metal complexes based on chiral biaryl ligands are readily prepared by a convenient amine elimination procedure, and they are efficient catalysts for the asymmetric hydroamination/cyclization of aminoalkenes. The biaryl-based ligands are highly modular enabling facile tuning of the catalyst reactivity and selectivity. The corresponding heterocyclic products have been obtained in excellent enantiomeric excesses (up to 93%) using sterically hindered C₂-symmetric titanium and zirconium mesitoylamidate complexes such as [1,1′-(C₁₀H₁₀)₂-2,2′-{NCO(2,4,6-Me₃C₆H₂)}₂]M(NMe₂)₂ (M = Ti, Zr). These results are presented in this short review.     

Nanocluster polyoxomolybdate supported on natural zeolite: a green and recyclable catalyst for epoxidation of alkenes

A heterogeneous catalyst for epoxidation of alkenes has been synthesized by introducing polyoxomolybdate into a natural zeolite as a solid and green support. The prepared catalyst was characterized by FT-IR, inductively coupled plasma optical emission spectrometry (ICP-OES), powder X-ray diffraction (XRD), N₂ absorption–desorption, field emission scanning electron micrograph (FE-SEM) and transmission electron microscopy (TEM). The catalytic investigations disclosed that nanocluster polyoxomolybdate supported on the surface is an active and recyclable catalyst in liquid phase alkene epoxidation in dichloroethane at 80 °C.     

The synthesis of 3-methyl- and 3,4-dimethyltetrahydroisoquinolines by intramolecular hydroamination with n-butyllithium

The synthesis of 3-methyltetrahydroisoquinolines and 3,4-dimethyltetrahydroisoquinolines from aromatic aminoalkenes using intramolecular hydroamination reactions, mediated by sub-stoichiometric amounts of n-butyllithium, is described.     

Origins of catalyst-controlled enantiodivergent hydroamination of enones with pyridazinones: A computational study

Density functional theory calculations have been performed to investigate the dipeptide phosphine-catalyzed hydroamination of enones with pyridazinones. The computations reveal that a number of the NH···O hydrogen-bonding interactions with the pyridazinone moiety and the C–H···O hydrogen-bonding interactions with the enone moiety are present in the enantioselectivity-determining Michael addition transition states. The experimentally-observed catalyst-controlled enantiodivergence is mainly attributed to the significant impact of the substituent of the amide moiety of the dipeptide phosphine on the relative strength of the NH···O hydrogen-bonding interactions, which was found to affect the Si face attack transition state, enabling the enantioselectivity switch upon change of chiral dipeptide phosphine catalyst.     

Cyclobutane ring formation by triflic imide catalyzed [2+2]-cycloaddition of allylsilanes

Cyclobutane forming [2+2]-cycloaddition reactions of allylsilane with electron-deficient olefin is promoted by triflic imide (Tf₂NH). Triflic imide is converted in situ to silyl triflic imide (R₃SiNTf₂), which serves as the actual catalyst for this process. When these reactions take place at higher than ambient temperatures, thermodynamically more stable anti-cyclobutanes are generated preferentially by equilibration of the initially formed adducts via retro [2+2]-cycloaddition.     

功能化含磷钼酸介孔硅材料的制备及其在深度氧化脱硫中的应用

随着全球工业的快速发展,化石燃料的消耗量日益增加,从而导致有毒污染物的排放量随之增加.燃料油中的含硫化合物燃烧后会形成SOx.SOx排放到大气中会形成酸雨污染环境.因此,超清洁燃料的生产迫在眉睫.目前主要的脱硫工艺为加氢脱硫(HDS).HDS能够有效脱除燃油中的硫醚、硫醇和二硫化物等含硫化物,但对于芳香族硫化物及其衍生物(如苯并噻吩、二苯并噻吩和4,6-二甲基二苯并噻吩等)的脱除效果较差,而且HDS需要在高温、高压且有合适催化剂存在的条件下进行反应.因此,开发操作简单、反应条件温和、能够高效脱除芳香族硫化物及其衍生物的脱硫工艺已成为目前研究的热点.催化氧化脱硫(CODS)能够在温和条件下高选择性脱除芳香族硫化物及其衍生物,作为HDS的有效补充,在深度脱硫领域的应用得到了广泛认可.目前适用于CODS的催化剂有分子筛、甲酸、过氧化物酶、氧化钼和杂多酸等.其中,含钼(VI)催化剂在CODS中表现出良好的性能,得到了广泛的研究和应用.在CODS中,催化剂载体同样起着重要作用.从实际应用角度出发,无定形二氧化硅在制备过程及经济性方面存在着不可替代的优势.到目前为止,无定形SiO2负载磷钼酸(HPMo)作为CODS催化剂的研究鲜有报道.本课题组以聚乙烯吡咯烷酮(PVP)为介孔模板剂,以正硅酸四乙酯(TEOS)为硅源,通过沉淀法直接合成了功能化含HPMo介孔复合材料HPMo-SiO2.采用XRD,FT-IR,31P-NMR和XPS等测试手段对所制备的材料进行了表征.结果表明,作为催化活性位点的钼以磷钼酸的形式存在,磷钼酸的Keggen结构在负载过程中没有遭到破坏,并且活性磷钼酸能够均匀分散在二氧化硅载体上.HPMo-SiO2的比表面积为365.0 m2/g,总孔容为1.237 cm3/g,平均孔径为12.91 nm.本文系统研究了模型油脱硫反应条件、催化剂循环使用次数及催化反应动力学.结果表明,HPMo-SiO2具有高效的脱硫活性,在反应温度为55oC,催化剂与模型油质量比为0.7%,反应时间为10 min的条件下,二苯并噻吩(DBT)脱除率可达100%;在反应温度为60oC,催化剂与模型油质量比为1.0%,反应时间为30 min的条件下,苯并噻吩(BT)脱除率可达100%.同等反应条件下,DBT的反应活性大于BT.DBT及BT的氧化脱除反应均符合表观一级动力学模型,且DBT脱除反应的表观活化能小于BT脱除反应.所制备的催化剂经过10次循环使用,DBT脱除率仍可以达到95.2%(BT为95.7%),说明所制备的HPMo-SiO2催化剂具有高活性和强稳定性.通过气质联用及微库仑仪对反应产物进行了分析,结果表明,BT和DBT的氧化产物分别为苯并噻吩砜(BTO2)和二苯并噻吩砜(DBTO2),且氧化产物全部被催化剂吸附,油品中没有含硫化合物的存在,因此不需要后续的氧化产物分离操作,提高了整个脱硫工艺的经济性,并且有效减少了分离操作带来的油品损失.     

Polyaniline supported vanadium catalyzed aerobic oxidation of alcohols to aldehydes and ketones

Polyaniline supported vanadium complex 1 catalyzes efficiently the oxidation of alcohols to aldehydes and ketones in high yields under molecular oxygen in toluene at ca. 100 °C. The catalyst 1 can be recycled without loss of activity.