Asymmetric Simmons-Smith Cyclopropanation Of α,β-Unsaturated Bornane-2,3-Diol Acetals

Reactionofselected α, β-unsaturated aldehydes with bornane-2-exo,3-cxo-diol has afforded a series of novel, chiral acetals which, on treatment with a Simmons-Smithreagent, undergo diastereoselective(46 - 70 %d.e.) cyclopropanatioa     

Unusual α-glycosylation with galactosyl donors with a C2 ester capable of neighboring group participation

Glycosylation of 4-methoxyphenyl 2,3,6-tri-O-benzoyl-β-d-glucopyranoside (2) with isopropyl 3-O-allyl-2,4,6-tri-O-benzoyl- (9) or 6-O-allyl-2,3,4-tri-O-benzoyl-1-thio-β-d-galactopyranoside (7) as the donor, afforded an α- and β-linked mixture, whereas with isopropyl 3-O-chloroacetyl-2-O-benzoyl-4,6-O-benzylidene- (13) and isopropyl 3-O-allyl-2-O-benzoyl-4,6-O-benzylidene-1-thio-β-d-galactopyranoside (15) as the donor, glycosylation of 2 gave α-linked products only, indicating that 4,6-O-benzylidenation led to α-stereoselectivity in spite of the C2 ester capable of neighboring group participation. Using 15 as the donor, glycosylation of mannose derivatives with 2- or 3-OH's, glucose with 2- or 3-OH's, galactose with 2-, or 3-, or 4-OH's, glucosamine and glucuronic acid with a 4-OH, and a lactose derivative with a 4-OH, also furnished α-linked products. However, when using 15 as the donor, glycosylation of aglycon alcohol or sugars with 6-OH's yielded normal β-linked products.     

Efficient Cluster-Based Catalysts for Asymmetric Hydrogenation of α-Unsaturated Carboxylic Acids

The new clusters [H(4) Ru(4) (CO)(10) (μ-1,2-P-P)], [H(4) Ru(4) (CO)(10) (1,1-P-P)] and [H(4) Ru(4) (CO)(11) (P-P)] (P-P=chiral diphosphine of the ferrocene-based Josiphos or Walphos ligand families) have been synthesised and characterised. The crystal and molecular structures of eleven clusters reveal that the coordination modes of the diphosphine in the [H(4) Ru(4) (CO)(10) (μ-1,2-P-P)] clusters are different for the Josiphos and the Walphos ligands. The Josiphos ligands bridge a metal-metal bond of the ruthenium tetrahedron in the "conventional" manner, that is, with both phosphine moieties coordinated in equatorial positions relative to a triangular face of the tetrahedron, whereas the phosphine moieties of the Walphos ligands coordinate in one axial and one equatorial position. The differences in the ligand size and the coordination mode between the two types of ligands appear to be reflected in a relative propensity for isomerisation; in solution, the [H(4) Ru(4) (CO)(10) (1,1-Walphos)] clusters isomerise to the corresponding [H(4) Ru(4) (CO)(10) (μ-1,2-Walphos)] clusters, whereas the Josiphos-containing clusters show no tendency to isomerisation in solution. The clusters have been tested as catalysts for asymmetric hydrogenation of four prochiral α-unsaturated carboxylic acids and the prochiral methyl ester (E)-methyl 2-methylbut-2-enoate. High conversion rates (>94?%) and selectivities of product formation were observed for almost all catalysts/catalyst precursors. The observed enantioselectivities were low or nonexistent for the Josiphos-containing clusters and catalyst (cluster) recovery was low, suggesting that cluster fragmentation takes place. On the other hand, excellent conversion rates (99-100?%), product selectivities (99-100?% in most cases) and good enantioselectivities, reaching 90?% enantiomeric excess (ee) in certain cases, were observed for the Walphos-containing clusters, and the clusters could be recovered in good yield after completed catalysis. Results from high-pressure NMR and IR studies, catalyst poisoning tests and comparison of catalytic properties of two [H(4) Ru(4) (CO)(10) (μ-1,2-P-P)] clusters (P-P=Walphos ligands) with the analogous mononuclear catalysts [Ru(P-P)(carboxylato)(2) ] suggest that these clusters may be the active catalytic species, or direct precursors of an active catalytic cluster species.     

Lewis acids as α-directing additives in glycosylations by using 2,3-O-carbonate-protected glucose and galactose thioglycoside donors based on preactivation protocol

Catalytic or stoichiometric amounts of Lewis acids were found to be very effective α-directing additives in the stereoselective glycosylations of diverse 2,3-O-carbonate-protected glucose and galactose thioglycoside donors by preactivation protocol. The poor stereoselectivities of 4,6-di-O-acetyl-2,3-O-carbonate protected thioglycoside donors in glycosyl coupling reactions were greatly improved, and excellent α-stereoselectivities were achieved by the addition of 0.2 equiv of BF(3)·OEt(2). On the other hand, the β-selectivities of 4,6-di-O-benzyl-2,3-O-carbonate-protected thioglucoside donor toward glycosylations were reversed completely to the α-selectivities by the use of 1 equiv of SnCl(4), making the stereoselectivity controllable. Furthermore, the poor stereoselectivities of 4,6-di-O-benzyl-2,3-O-carbonate-protected thiogalactoside donor in glycosylations were also improved by using SnCl(4) as additive.     

Synthetic Utility of α-Stannyl α,β-Unsaturated Esters as Reagents for β-Substituted Acrylate α-Anion Synthons: Tin-Lithium Exchange and Palladium-Catalized Coupling Reactions

The tin-lithium exchange and the palladium-catalized coupling reactions of the title compounds have been studied. The latter reaction was found to be more efficient for functionalizing the α-carbon of these esters.     

Polyaniline-Anchored Metal Salts for Michael Reaction of α,β-Unsaturated Ketones

A catalyst consisting of polyaniline-anchored metal salts is used as a Lewis acid to promote the Michael reaction of α,β-unsaturated ketones. The reaction is performed efficiently with imidazole, acetyl acetone, and ethyl acetate as Michel donors and chalcones as the acceptors under ultrasound irradiation.     

Oligophenylenaminones as scaffolds for α-helix mimicry

The design and synthesis of small molecule α-helix mimetics has been a productive field over the past decade. These compounds have performed well in a variety of biological systems as functional disruptors of α-helix-mediated protein-protein interactions. In our studies we have continued to develop novel, more biologically compatible scaffolds, which are often easier to assemble and capable of mimicking longer and/or more diverse helices. To this end, we have constructed a new series of i, i+4, i+7 α-helix mimics based on the enaminone scaffold. These molecules represent a step forward in the pursuit of idealized monofacial α-helix mimetics.     

Photocontrolled Cobalt Catalysis for Selective Hydroboration of α,β-Unsaturated Ketones

Selectivity between 1,2 and 1,4 addition of a nucleophile to an α,β-unsaturated carbonyl compound has classically been modified by the addition of stoichiometric additives to the substrate or reagent to increase their “hard” or “soft” character. Here, we demonstrate a conceptually distinct approach that instead relies on controlling the coordination sphere of a catalyst with visible light. In this way, we bias the reaction down two divergent pathways, giving contrasting products in the catalytic hydroboration of α,β-unsaturated ketones. This includes direct access to previously elusive cyclic enolborates, via 1,4-selective hydroboration, providing a straightforward and stereoselective route to rare syn-aldol products in one-pot. DFT calculations and mechanistic experiments confirm two different mechanisms are operative, underpinning this unusual photocontrolled selectivity switch.     

Mesoporous silica particles for selective detection of dopamine with β-cyclodextrin as the selective barricade

A mesoporous silica nanoparticle (MSN) based fluorescent sensor for dopamine was constructed with probes inside particle pores and β-cyclodextrin (β-CD) molecules on the particle surface as the selective barricade. The synergistic action of both the hydrophilic rim and hydrophobic cavity of β-CD ensures that the sensor can distinguish dopamine from other biological competitors.     

Aza-Michael Addition of Amines to α,β-Unsaturated Compounds Using Molecular Iodine as Catalyst

Aza-Michael adducts are obtained in very good yields by the conjugate addition of aliphatic amines to α,β-unsaturated compounds using molecular iodine as catalyst in dichloromethane at room temperature. Aromatic amines were found to be reactive under reflux in toluene.     

Charge-enhanced thiourea catalysts as hydrogen bond donors for Friedel‒Crafts Alkylations

Charge-enhanced catalysis has emerged as a powerful alternative to the mainstream use of neutral catalysis.With this in mind, we report a catalytic Friedel?Crafts alkylation method catalyzed by a charged thiourea incorporating a cationic cyclopropenium moiety. Mechanistic studies, including density functional theory computational calculations, variable time normalization analysis, and ¹H NMR binding studies, collectively reveal this charge-enhanced reactivity proceeds by a dual hydrogen bond-mediated LUMO-lowering mode of substrate activation. Key to these findings is the observed steady-state concentration of the catalyst with in situ derived monomeric catalytic species predominating under the reaction conditions.     

Chemisorbed dimethylammonium chlorochromate as selective oxidants for primary and second aryAlcohols

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A fluorescent molecular ruler as a selective probe for ω-aminoacids

A fluorescent probe for ω-aminoacids behaves as a molecular ruler, changing the yellow fluorescent emission into blue as a function of the distance between the terminal ammonium and the carboxylate groups, permitting the quantitative detection of ω-aminoacids, their metabolites and related drugs, such as pregabalin or gabapentin, from pharmaceutical formulations.     

A Protocol for Accessing the β-Azidation of α,β-Unsaturated Carboxylic Acids

This contribution reports the preparation and use of a new immobilized catalyst, PS-DABCOF (9), which has been specifically designed to access for the first time the efficient β-azidation of α,β-unsaturated carboxylic acids.     

Highly selective nickel-catalyzed methyl-carboxylation of homopropargylic alcohols for α-alkylidene-γ-butyrolactones

A first practical Ni(0)-catalyzed highly stereoselective methyl-carboxylation of homopropargylic alcohols with ZnMe(2) and CO(2) for the efficient synthesis of α-alkylidene-γ-butyrolactones is described. The reaction may be applied to other alkynols.     

Stereoselective Synthesis of Sulfonyl-substituted trans-2,3-Dihydrofuran Derivatives via Reaction of Arsonium Ylides with α,β-Unsaturated Ketones

Trans-2,3-dihydrofuran derivatives 3 or 4 substituted with a sulfonyl group were prepared with high chemoselectivity and good yields by [1＋4]-addition reaction of α,β-unsaturated ketones 1 with arsonium bromide 2 in CH2Cl2 in the presence of potassium carbonate at room temperature.The structures of the products were characterized by IR,MS,^1H NMR,elemental analysis and single crystal X-ray diffraction analysis.A mechanism for the formation of products was also proposed.     

Naphthalene-cholesterol conjugate as simple gelator for selective sensing of CN– ion

Cholesterol-based Schiff base 1 has been designed and synthesised. The Schiff base 1 forms yellow coloured gel in DMF:H₂O (2:1, v/v) and the gel is anion responsive. Among different anions, the gel phase of 1 is selectively transformed into sol in the presence of CN^– ions and validates its visual sensing. ¹H NMR, FTIR and HRMS spectroscopic techniques were adopted to study the gelation of 1 and its responsive behaviour towards anions.     

Mild and Efficient Procedure for Michael Addition of N-Heterocycles to α,β-Unsaturated Compounds Using Anhydrous K3PO4 as Catalyst

Imidazole, 1,2,4-triazole, indole, and benzotriazole undergo conjugate additions with α, β-unsaturated carbonyl compounds in the presence of anhydrous potassium phosphate at ambient temperature to afford the corresponding Michael adducts in excellent yields.     

2-Phenylbenzimidazoline as a Reducing Agent in the Preparation of Malononitriles from α,β-Unsaturated Dinitriles

The development of methods applicable to the selective reduction of carbon-carbon double bonds conjugated with strong electronwithdrawing group such as cyano, nitro, ester or sulfonate group has been a synthetic subject. Although several procedures¹⁾ have been employed for such selective reduction, virtually no sufficient method is known. Recently we have found²⁾ that benzylmalononitriles and 2-nitroethylbenzenes were obtained in good yields by the reactions of benzylidene-malononitriles and β-nitrostyrenes with a half molar amount of o-phenylenediamine (1), and showed that the products resulted from the reduction of the olefins by 2-phenylbenzimidazolines formed from equimolar amounts of the olefins and diamine (1). However, this reaction mode is not effective as a synthetic procedure for the reduction of the olefins because a half molar amount of the olefins is consumed to form 2-phenylbenzimidazolines.     

Triphenylamine/tetracyanobutadiene-based D-A-D π-conjugated systems as molecular donors for organic solar cells

Thiophene-based D-A-D π-conjugated systems containing triphenylamine end groups connected to a 1,1,4,4-tetracyanobuta-1,3-diene acceptor by oligothiophene chains of variable length have been synthesized. These compounds show interesting light-harvesting properties and low-lying HOMO levels. Preliminary results on bilayer heterojunction solar cells with C(60) as acceptor show power conversion efficiency higher than 1.0%.