Synergistic catalysis of anthrone Diels-Alder reactions

[reaction: see text] The combination of an amine base and Lewis acid (Li+) leads to synergistic catalysis of the Diels-Alder reaction of anthrone with methyl crotonate and some other less reactive dienophiles. These cycloadditions either do not occur with the individual catalysts used separately or they are greatly accelerated by the combined catalysts. DMSO solvent allows the use of LiCl as the Lewis acid source and can provide greater control of subsequent conversion to Michael adduct.     

Axially chiral amidinium ions as inducers of enantioselectivity in Diels-Alder reactions

[reaction: see text] Enantioselective catalysis of Diels-Alder reactions is mostly achieved by coordinating the dienophile to relatively strong chiral Lewis acids. Here we report on a novel approach employing the hydrogen-bond-mediated association of dienophiles to chiral host molecules. In a reaction forming the steroid skeleton of norgestrel, chiral amidinium ions induce 5:ent-5 ratios of up to 2.5:1. Improved and simplified amidinium catalysts may become interesting candidates to perform stereoselective transformations.     

Oxazaborolidinone-catalyzed enantioselective Diels-Alder reaction of acyclic alpha,beta-unsaturated ketones

allo-Threonine-derived O-acyl-B-phenyl-oxazaborolidinones are demonstrated to be powerful and highly enantioselective Lewis acid catalysts for the Diels-Alder reaction of simple acyclic enone dienophiles, expanding the scope of ketone dienophiles and dienes. With 10 to 20 mol % of catalyst, the Diels-Alder adducts are obtained in 76-98% ee with high endo-selectivity. The catalyst exhibits high activity for the reaction with the less reactive beta-substituted dienophiles and the less reactive 1,3-cycohexadiene and 1,3-butadiene derivatives. The application of the catalysts to the Diels-Alder reaction of furan is also described.     

The first general enantioselective catalytic Diels-Alder reaction with simple alpha,beta-unsaturated ketones

The first general approach to enantioselective catalysis of the Diels-Alder reaction with simple ketone dienophiles has been accomplished. The use of iminium catalysis has enabled enantioselective access to a fundamental Diels-Alder reaction variant that has previously been unavailable using chiral Lewis acid catalysis. A new chiral amine catalyst has been developed that allows a variety of monodentate cyclic and acyclic ketones to successfully participate in enantioselective [4 + 2] cycloadditions. A wide spectrum of cyclic and acyclic diene substrates can also be accommodated in this new organocatalytic transformation. A computational model is provided that is in accord with the sense of enantioinduction observed for all reactions conducted during the course of this study.     

Catalysis in Single Crystalline Materials: From Discrete Molecules to Metal-Organic Frameworks

Catalysis is one of the key techniques for people's modern life. It has created numerous essential chemicals such as biomedicines, agricultural chemicals and unique materials. Heterogeneous catalysis is the new emerging method with reusable catalysts. Among heterogenous catalysis patterns developed so far, single crystalline catalysis has become the promising one owing to its high catalytic density and selectivity resulted by the inherent porosity, orderliness of the lattices and permeability. These crystalline catalysts could be used in various reactions such as photo-dimerization, Diels-Alder reaction, CO₂ transformation and so on. In this review, we highlighted the reported works about the single crystalline catalysts. Both discrete small molecules and metal-organic frameworks (MOFs) have been used to prepare single crystals for catalysis. For discrete molecules based crystalline catalysts, coordinated and covalent molecules have been used. There were more catalytic modes in crystalline MOF catalysts. Three patterns were identified in this review: single crystalline MOFs i) without catalytic sites, ii) with inherent catalytic features and iii) with introducing catalytic units by post synthetic modification. Based on these examples, this review committed to provide the inspirations for the further design and application of single crystalline materials.     

CuO and Ag2O/CuO catalyzed oxidation of aldehydes to the corresponding carboxylic acids by molecular oxygen

Furfural was oxidized to furoic acid by molecular oxygen under catalysis by 150 nm-sized Ag(2)O/CuO (92%) or simply CuO (86.6%). When 30 nm-size catalyst was used,the main product was a furfural Diels-Alder adduct. Detailed reaction conditions and regeneration of catalysts were investigated. Under optimal conditions, a series of aromatic and aliphatic aldehydes were oxidized to the corresponding acids in good yields.     

The preparation and utility of bis(sulfinyl)imidoamidine ligands for the copper-catalyzed Diels-Alder reaction

The design and preparation of a novel class of ligands based on the sulfinyl imine functionality is described. In particular, an efficient and modular synthesis of bis(sulfinyl)imidoamidine (siam) ligands is reported. The versatility of the synthetic sequence is demonstrated by the preparation of various analogues to explore the effect of substitution about the ligand framework on catalytic activity. The utility of the siam ligands in asymmetric catalysis is demonstrated in the Cu(II)-catalyzed Diels-Alder reaction where highly enantio- and diastereoselective reactions are reported for a range of N-acyloxazolidinone dienophile and diene substrate combinations. Of particular note is the efficiency of these asymmetric catalysts for reactions involving challenging and relatively unreactive acyclic diene substrates. Finally, structural data are provided for several ligands as well as metal-ligand complexes.     

Catalysis of the cleavage of uridine 3'-2,2,2-trichloroethylphosphate by a designed helix-loop-helix motif peptide

A 42-residue peptide that folds into a helix-loop-helix motif and dimerizes to form a four-helix bundle has been designed to catalyze the hydrolysis of phosphodiesters. The active site on the surface of the folded catalyst is composed of two histidine and four arginine residues, with the capacity to provide general acid, general base, and/or nucleophilic catalysis as well as transition state stabilization. Uridine 3'-2,2,2 trichloroethylphosphate (2) is a mimic of RNA with a leaving group pKa of 12.3. Its hydrolysis is energetically less favorable than that of commonly used model substrates with p-nitrophenyl leaving groups and therefore a more realistic model for the design of catalysts capable of cleaving RNA. The second-order rate constant for the hydrolysis of 2 at pH 7.0 by the polypeptide catalyst was 418 x 10(-6) M-1 s-1, and that of the imidazole catalyzed reaction was 1.66 x 10(-6) M-1 s-1. The pH dependence suggested that catalysis is due to the unprotonated form of a residue with a pKa of around 5.3, and the observed kinetic solvent isotope effect of 1.9 showed that there is significant hydrogen bonding in the transition state, consistent with general acid-base catalysis. The rate constant ratio k2(Pep)/k2(Im) of 252 is probably due to a combination of nucleophilic and general acid-base catalysis, as well as transition state stabilization. Substrate binding was weak since no sign of saturation kinetics was observed for substrate concentrations in the range from 5 to 40 mM. The results provide a platform for the further development of catalysts for RNA cleavage with a potential role in the development of drugs.     

Synthesis of novel dendritic 2,2'-bipyridine ligands and their application to Lewis acid-catalyzed diels-alder and three-component condensation reactions

A series of dendritic ligands with a 2,2'-bipyridine core was synthesized through the coupling of 4,4'-dihydroxy-2,2'-bipyridine with poly(aryl ether) dendrons. The corresponding dendritic Cu(OTf)2 catalysts were used for Diels-Alder and three-component condensation reactions. The dendritic Cu(OTf)2-catalyzed Diels-Alder reaction proceeded smoothly, and these dendritic catalysts could be recycled without deactivation by reprecipitation. Three-component condensation reactions such as Mannich-type reactions also proceeded not only in dichloromethane but also in water. Furthermore, a positive dendritic effect on chemical yields was observed in both Diels-Alder reactions and aqueous-media three-component condensation reactions.     

Complexation of Neutral Molecules by Cyclophane Hosts

Since the discovery of the crown ethers by Pedersen twenty years ago, the chemistry of synthetic hosts for the selective complexation of organic and inorganic guests has seen an extraordinarily rapid development. This article discusses in particular the contributions provided by synthetic cyclophanes as hosts to the understanding of molecular complexation of neutral organic guest molecules in aqueous and organic solvents. In aqueous solution, cyclophanes form stoichiometric complexes with neutral aromatic guests which can approach enzyme-substrate complexes in their stability. Efficient molecular complexation is also observed in organic environments. Here, as a result of large solvation effects, the strength of complexation is strongly dependent on the nature of the organic solvent. Electron donor-acceptor interactions can contribute significantly to the stability of complexes formed between cyclophane hosts and aromatic guests. Force-field calculations together with computer graphics are powerful tools in the design of water-soluble, optically active hosts for chiral recognition of complexed racemic guests. Simple and selective functionalization of the cyclophane framework leads to stable, bioorganic catalysts. Like enzymes, these catalysts bind their substrates in a rapid equilibrium prior to the reaction steps. As a perspective, some fascinating research objectives in the field of molecular recognition and catalysis which can be targeted with designed cyclophane hosts are shown.     

Keggin杂多酸负载型催化剂研究及在有机合成中的应用

评述了负载型杂多酸Keggin结构催化剂的制备、表征及其表面作用机理, 阐述了在非均相催化酯化反应、Friedel-Crafts烷基化和酰基化反应、选择氧化、不对称催化反应、异构化反应、缩合反应、裂解反应、水合反应、脱水反应、水解反应、重排反应、Diels-Alder反应及醚化反应等作为探针反应的催化性能, 总结了重排反应、醇氧化等不同类型催化反应的反应机理和催化剂失活的主要原因以及影响负载型催化剂水热稳定性能的因素, 指出了负载型杂多酸Keggin结构催化剂研究中有待解决的问题及今后的发展方向..     

Catalytic Asymmetric Hetero-Diels-Alder Reactions of Carbonyl Compounds and Imines

Asymmetric catalysis is a challenge for chemists: How can we design catalysts to achieve the goal of forming optically active compounds? This review provides the reader with an overview of the development of catalytic asymmetric hetero-Diels-Alder reactions of carbonyl compounds and imines. Since its discovery, the Diels-Alder reaction has undergone intensive development and is of fundamental importance for synthetic, physical, and theoretical chemists. The Diels-Alder reaction has been through different stages of development, and at the beginning of the 21st century catalytic Diels-Alder reactions are one of the main areas of focus. The preparation of numerous compounds of importance for our society is based on cycloaddition reactions to carbonyl compounds and imines. There are several parallels between the reactions of carbonyl compounds and those of imines, which, however, begin to vanish on entering the field of catalytic reactions. Why? From a mechanistic point of view some similarities can be drawn, but the synthetic development of catalytic enantioselective hetero-Diels-Alder reactions of imines are several years behind those of the carbonyl compounds. For hetero-Diels-Alder reactions of carbonyl compounds there a number of different chiral catalysts, and great progress has been achieved in developing enantioselective reactions for unactivated and activated carbonyl compounds. In contrast the development of catalytic enantioselective hetero-Diels-Alder reactions of imines is in its infancy and only few catalytic reactions have been published. This review will focus on the most important developments, and discuss the synthetic and mechanistic aspects of enantioselective hetero-Diels-Alder reactions of carbonyl compounds catalyzed by chiral Lewis acids. For the hetero-Diels-Alder reactions of imines, the diastereoselective reactions of optically substrates catalyzed by Lewis acids will be presented first, followed by the catalytic enantioselective reactions.     

Tandem hetero diels-alder reaction: synthesis of oxygenated macrocycles

[structure: see text]. C2-symmetric, oxygenated macrocycles have been synthesized from simple acyclic precursors in a single step by a tandem hetero Diels-Alder reaction. Thermolysis and Lewis acid catalysis can effect this novel transformation. The tandem reaction product is formed in preference to the intramolecular cycloaddition product, and an explanation for this result is proposed.     

Towards organo-click chemistry: development of organocatalytic multicomponent reactions through combinations of aldol, Wittig, Knoevenagel, Michael, Diels-Alder and Huisgen cycloaddition reactions

Here we report on our studies on combinations of amino acids and copper(I) for catalyzing multicomponent reactions (MCRs). We aimed to prepare both diene and dienophiles simultaneously, under very mild and environmentally friendly conditions, thus giving the constituents for a stereocontrolled Diels-Alder reaction, which in turn yields compounds 4 to 8. A diversity-oriented synthesis of polysubstituted spirotriones 4 to 6 were assembled from simple substrates like 1-(triphenylphosphanylidene)-propan-2-one, two aldehydes, and cyclic-1,3-diketones through Wittig/Knoevenagel/Diels-Alder and aldol/Knoevenagel/Diels-Alder reaction sequences in one pot under stereospecific organocatalysis. Chemical diversity libraries of polysubstituted spirotrione-1,2,3-traizoles 8 were assembled from simple substrates by means of Wittig/Knoevenagel/Diels-Alder/Huisgen cycloaddition reaction sequences in one pot under stereospecific organo/Cu(I) catalysis. Functionalized dispirolactones such as 6 are biologically active antioxidants and radical scavengers, and spirotrione-1,2,3-traizoles 8 have found wide applications in chemistry, biology, and materials science. Experimentally simple and environmentally friendly, organocatalytic, asymmetric four-component Diels-Alder (AFCDA) reactions of 1-(triphenylphosphanylidene)- propan-2-one, two different aldehydes, and cyclic-1,3-diketones produced diastereospecific and highly enantioselective substituted spirotriones 4 by means of a Wittig/Knoevenagel/Diels-Alder reaction sequence in one pot. Additionally we have developed an organocatalytic, asymmetric three-component Michael (ATCM) reaction of 1-(triphenylphosphanylidene)-propan-2-one, aldehyde, and cyclic-1,3-diketones that produced Michael adducts 15, 16 through a Wittig/Michael reaction sequence in a highly enantioselective one-pot process.     

梳形接枝共聚物的合成(Ⅱ)——载体化钌卡宾络合物催化降冰片烯基聚苯乙烯的开环岐化聚合

由石油化工副产C₅馏份提取双环戊二烯(DCPD)、以聚合物负载三氟化硼为催化剂进行DCPD与烯丙基氯(AC)的Diels-Alder反应合成5-氯甲基-2-降冰片烯(NBCH₂Cl),经锂代反应后用以引发苯乙烯的活性阴离子聚合合成了降冰片烯(NB)基聚苯乙烯(PS)大分子环烯单体NB-PS,在聚合物负载钌卡宾络合物[RuCl₂(PPh₃)₂(=C=CHtBu)]催化(引发)作用下进行大分子单体NB-PS的开环歧化聚合(ROMP)合成了梳形接枝共聚物PNB-g-PS.实验结果表明所合成聚合物负载硼、钌络合物催化剂的性能均明显优于对应非负载体.讨论了上述催化剂的聚合物载体效应的机理及温度、溶剂等对活性阴离子聚合反应的影响.     

Diastereoselective diels-alder reactions of optically-active vinyl sulphoxides

The Diels-Alder reaction of an optically active vinyl sulphoxide containing a second electron withdrawing group with cyclopentadiene gave separable diastereomers. The effect of Lewis acid catalysis on the reaction was studied. Reaction of an acetylenic anion with menthyl p-toluene sulphinate gave an anomalous product.     

SYNTHESIS OF A COMB GRAFT COPOLYMER VIA RING OPENING METATHESIS POLYMERIZATION CATALYZED BY SUPPORTED RHUTHENIUM CARBENE COMPLEX

Comb graft copolymers (CGC), a special kind of the hyper-branched polymer series, have unique and excellent properties [1,2]. Synthesizing CGC via ring opening metathesis polymerization (ROMP) of cycloolefinyl macromonomer catalyzed (initiated) by the molybdenum carbene complex (Schrock complex) is a newly-developed method [3,4]. Though showing excellent catalytic behavior the complex has the disadvantage of highly moisture and oxygen sensitive and is hence operation-inconvenient. We repor…     

DNA-based asymmetric catalysis: sequence-dependent rate acceleration and enantioselectivity

This study shows that the role of DNA in the DNA-based enantioselective Diels-Alder reaction of azachalcone with cyclopentadiene is not limited to that of a chiral scaffold. DNA in combination with the copper complex of 4,4'-dimethyl-2,2'-bipyridine (Cu-L1) gives rise to a rate acceleration of up to 2 orders of magnitude compared to Cu-L1 catalysis alone. Furthermore, both the enantioselectivity and the rate enhancement prove to be dependent on the DNA-sequence. These features are the main reasons for the efficient and enantioselective catalysis observed with salmon testes DNA/Cu-L1 in the Diels-Alder reaction. The fact that absolute levels of stereocontrol can be achieved with a simple and weak DNA-binding complex like Cu-L1 is a clear demonstration of the power of the supramolecular approach to hybrid catalysis.     

SYNTHESIS OF A COMB GRAFT COPOLYMER VIA RING OPENING METATHESIS POLYMERIZATION CATALYZED BY SUPPORTED RHUTHENIUM CARBENE COMPLEX

5－Chloromethyl-2-norbornene was synthesized via Diels-alder reaction of cyclopentadiene and allyl chloride using a polymer supported boron trifluoride as the catalyst,and was then lithiated and used to initiate a livcing anionic polymerization of styrene to prepare a macromonome,5-polystryl-2-norbornene NB-PS,Comb graft copolymer PNB-g-PS was synthesized via ring opening metathesis polymerization of the macromonomer under the catalysis of ruthenium carbene complex RuCl2(PPh3)2(=CCHtBu)and its polymer supported correspondent.Experimetal results showed that the behavior of both the supported boron and supported ruthenium catalysts are superior to their unsupported counterparts.The possible promotion mechanism of the tailor-made supports is discussed.     

Synthesis of a carbasugar analogue of a putative intermediate in the UDP-galp-mutase catalyzed isomerization

[reaction: see text] The synthesis of the carbasugar analogue of 1,4-anhydro-beta-d-galactopyranose, a proposed intermediate in the reaction catalyzed by uridine diphosphate-alpha-d-Galp mutase, in racemic form via Diels-Alder and Barton decarboxylation chemistry is reported. This compound was found not to inhibit the mutase from Mycobacterium tuberculosis, indicating that the enzyme does not possess a 1,4-anhydro-beta-d-galactopyranose binding pocket.