Side‐Arm Effect of a Methyl α‐d‐Glucopyranoside Based Lariat Ether Catalysts in Asymmetric Syntheses

Methyl α‐d ‐glucopyranoside based monoaza‐15‐crown‐5 type lariat ethers with different heteroatom‐containing side arm attached to the nitrogen of the macrocyclic ring have been synthesized. These compounds were used as chiral phase transfer catalysts in a few asymmetric reactions, such as Michael additions, Darzens condensation, and epoxidation of chalcone. The side arms of the macrocycles had a significant impact on the chemical yields and the enantioselectivity. The effect of the lariat ethers with side arms having heteroatom (O, N, and S) was compared with the effect of the analogues having substituents without a heteroatom. The terminal allyl group also generated a significant enantioselectivity (79% enantiomeric excess) in one of the Michael additions. The application of crown ethers with substituents (CH₂)₃OH or (CH₂)₃OCH₃ leads to the best enantioselectivities 85% and 99%, respectively.     

H2S splitting on Cu(110): Insight from combined periodic density functional theory calculations and microkinetic simulation

Practical copper (Cu)‐based catalysts for the water–gas shift (WGS) reaction was long believed to expose a large proportion of Cu(110) planes. In this work, as an important first step toward addressing sulfur poisoning of these catalysts, the detailed mechanism for the splitting of hydrogen sulfide (H₂S) on the open Cu(110) facet has been investigated in the framework of periodic, self‐consistent density functional theory (DFT‐GGA). The microkinetic model based on the first‐principles calculations has also been developed to quantitatively evaluate the two considered decomposition routes for yielding surface atomic sulfur (S*): (1) H₂S → H₂S* → SH* → S* and (2) 2H₂S → 2H₂S* → 2SH* → S* + H₂S* → S* + H₂S. The first pathway proceeding through unimolecular SH* dissociation was identified to be feasible, whereas the second pathway involving bimolecular SH* disproportionation made no contribution to S* formation. The molecular adsorption of H₂S is the slowest elementary step of its full decomposition, being related with the large entropy term of the gas‐phase reactant under realistic reaction conditions. A comparison of thermodynamic and kinetic reactivity between the substrate and the close‐packed Cu(111) surface further shows that a loosely packed facet can promote the S* formation from H₂S on Cu, thus revealing that the reaction process is structure sensitive. The present DFT and microkinetic modeling results provide a reasonably complete picture for the chemistry of H₂S on the Cu(110) surface, which is a necessary basis for the design of new sulfur‐tolerant WGS catalysts. © 2013 Wiley Periodicals, Inc.     

Asymmetric α-Acetoxylation of Carboxylic Esters. Preliminary Communication

Using the readily accessible chiral auxiliaries 1 – 3 the sulfonamide-shielded O-silylated esters 5 underwent π-face-selective α-acetoxylation on successive treatment with Pb(OAc)₄ and NEt₃ HF to give after recrystallization α-acetoxy ester 6 in 55–67% yields and in 95–100% d.e. Starting from conjugated enoates addition of RCu and subsequent acetoxylation 10 → 11 → 12 yielded α,β-bifunctionalized esters 12 with >95% configurational control at both C_α and C_β. Nondestructive removal of the auxiliary ( 6 → 7 , 6 → 8 and 12 → 13 ) gave either α-hydroxycarboxylic acids or terminal α-glycols in high enantiomeric purity. The prepared glycols 8c and 13a are key intermediates for previously reported syntheses of the natural products 16 and 17 , respectively.     

Adsorption of I2 by Macrocyclic Polyazadithiophenolato Complexes Mediated by Charge‐Transfer Interactions

The macrocyclic complex [Ni₂(L)(OAc)]ClO₄ ( 1 ) adsorbs up to 17 molar equivalents (>270 wt %) of iodine, although it does not exhibit permanent porosity. Vibrational spectroscopic and crystallographic studies reveal that two I₂ molecules are captured by means of thiophenolate→I₂ charge‐transfer interactions, which enable the diffusion and sorption of further I₂ molecules in a polyiodide‐like network. The efficient sorption and desorption characteristics make this material suitable for accommodation, sensing, and slow release of I₂.     

Retracted: The Manganese(I)-Catalyzed Asymmetric Transfer Hydrogenation of Ketones: Disclosing the Macrocylic Privilege

The bis(carbonyl) manganese(I) complex [Mn(CO)₂( 1 )]Br ( 2 ) with a chiral (NH)₂P₂ macrocyclic ligand ( 1 ) catalyzes the asymmetric transfer hydrogenation of polar double bonds with 2-propanol as the hydrogen source. Ketones (43 substrates) are reduced to alcohols in high yields (up to >99 %) and with excellent enantioselectivities (90–99 % ee). A stereochemical model based on attractive CH–π interactions is proposed.     

Retracted: The Manganese(I)‐Catalyzed Asymmetric Transfer Hydrogenation of Ketones: Disclosing the Macrocylic Privilege

The bis(carbonyl) manganese(I) complex [Mn(CO)₂( 1 )]Br ( 2 ) with a chiral (NH)₂P₂ macrocyclic ligand ( 1 ) catalyzes the asymmetric transfer hydrogenation of polar double bonds with 2‐propanol as the hydrogen source. Ketones (43 substrates) are reduced to alcohols in high yields (up to >99 %) and with excellent enantioselectivities (90–99 % ee). A stereochemical model based on attractive CH–π interactions is proposed.     

[FeIII(F20‐tpp)Cl] Is an Effective Catalyst for Nitrene Transfer Reactions and Amination of Saturated Hydrocarbons with Sulfonyl and Aryl Azides as Nitrogen Source under Thermal and Microwave‐Assisted Conditions

[Fe^III(F₂₀‐tpp)Cl] (F₂₀‐tpp=meso‐tetrakis(pentafluorophenyl)porphyrinato dianion) is an effective catalyst for imido/nitrene insertion reactions using sulfonyl and aryl azides as nitrogen source. Under thermal conditions, aziridination of aryl and alkyl alkenes (16 examples, 60–95 % yields), sulfimidation of sulfides (11 examples, 76–96 % yields), allylic amidation/amination of α‐methylstyrenes (15 examples, 68–83 % yields), and amination of saturated C? H bonds including that of cycloalkanes and adamantane (eight examples, 64–80 % yields) can be accomplished by using 2 mol % [Fe^III(F₂₀‐tpp)Cl] as catalyst. Under microwave irradiation conditions, the reaction time of aziridination (four examples), allylic amination (five examples), sulfimidation (two examples), and amination of saturated C? H bonds (three examples) can be reduced by up to 16‐fold (24–48 versus 1.5–6 h) without significantly affecting the product yield and substrate conversion.     

New Chiral Macrocyclic Compounds from D-Mannitol

We have recently reported the synthesis of new chiral macrocyclic polyhydroxyethers by reduction of cyclodextrins 1. These compounds display appreciable conformational freedom in solution as it occurs with the ionophores. Our chiral macrocycles may be considered as built by units of alditol (1 → 4) alditols. Such units, conveniently substituted, prepared by us by reduction of disaccharide derivatives2, are possible synthons for the synthesis of other macrocyclic polyhydroxyethers in which the nature and number of alditol (1 → n) alditol components can be varied at will. We are interested in the preparation and the structural studies of these type of receptors since the synthesis of new chiral macrocycles is a topic of interest and the building of chiral cavities may be of importance in the study of host-guest interactions. We now report on the preparation, from D-mannitol, a readily available starting material with C₂symmetry, and tetraethylene glycol, of the chiral macrocycles 1, 2, and 3, as model compounds in exploring the synthesis of more complex macrocyclic polyhydroxyethers derived from alditol (1 → n) alditol. Other macrocyclic compounds from D mannitol have been previously synthesised.     

Synthesis and Structural Characterization of Three Novel Macrocyclic Coordination Complexes Formed by Self-assembly of Bridged Bi-or Tetrapyridine with Transition Metal Salts

Serf-assembly of a ferrocenyl-bridged bipyridine ligand bpef [bpef=1, 1＇-bis（trans-2-pyrid-4＇-ylethenyl）ferrocene] with silver triflate in CH2Cl2/MeOH or mercuric diiodide in MeCN/CH2Cl2 gave the corresponding macrocyclic coordination complexes [bpef]2[AgSO3CF3]2 （1） and [bpef]2[Hg3I6] （2） in 93% and 89% yields, respectively, whereas the pentaerythritolyl-bridged tetrapyridine ligand ptpc [ptpc=pentaerythritol tetrakis-（4-pyridinecarboxylate）] reacted with cobalt thiocyanate via self-assembly to afford the macrocyclic coordination polymer [Co（NCS）2（ptpc）], （3） in 90% yield. The X-ray diffraction analyses for 1-3 confirmed their novel macrocyclic structures and revealed that （i） the two silver atoms in complex 1 have an essentially linear geometry with N-Ag-N bond angle of 175.7° and 172.9°, （ii） the geometry of the middle mercury atom in complex 2 is square-planar, while the other two mercury atoms in the other two complexes are tetrahedral, and （iii） all the cobalt atoms in complex 3 adopt an octahedral geometry. In addition, the synthetic procedure for the known tetrapyridine ligand ptpc has been improved.     

Regiospecific Anomerisation of Acylated Glycosyl Azides and Benzoylated Disaccharides by Using TiCl4

Chelation induced anomerisation is promoted when Lewis acids, such as TiCl₄ or SnCl₄, coordinate to the pyranose ring oxygen atom and another site, giving rise to endocyclic cleavage and isomerisation to the more stable anomer. In this research regiospecific site‐directed anomerisation is demonstrated. TiCl₄ (2.5 equiv) was employed to induce anomerisation of 15 glycosyl azide and disaccharide substrates of low reactivity, and high yields (>75 %) and stereoselectivies (α/β>9:1) were achieved. The examples included glucopyranuronate, galactopyranuronate and mannopyranuronate as well as N‐acetylated glucopyranuronate and galactopyranuronate derivatives. A disaccharide with the α1→4 linkage found in polygalacturonan was included. The use of benzoylated saccharides was found to be important in disaccharide anomerisation as attempts to isomerise related acetyl protected and 2,3‐carbonate protected derivatives were not successful.     

Stochastic model for triplet yields

A stochastic model of triplet yields is considered where the singlet S₁ is initially excited and subsequently feeds the triplet T₁. Both S₁ and T₁ have Montroll—Shuler step ladder vibrational relaxation mechanisms and radiative and non-radiative decay rates that vary linearly with increasing vibrational energy. Assuming the S₁ → T₁ rates also have this linear variation, the kinetic model is exactly solved in terms of integrals of simple functions of hyperbolic functions. The predictions of the model are illustrated by application to naphthalene. The model parameters are chosen; wherever possible, from experimental data. The predictions are in gross qualitative agreement with available experiments on triplet yields, and they indicate more detailed future experiments to separate the S₁ → T₁ and S₁ → S₀ (ground singlet) decays (and their energy dependence) in aromatic hydrocarbons.     

Synthese makrocyclischer Ketone durch Ringerweiterung; ein neuer Weg zu(±)-Muscon

Synthesis of Macrocyclic Ketones by Ring-Enlargement Reactions; a New Path to (±)-Muscone A new synthetic route to macrocyclic ketones is described. Starting from 2-nitrocycloalkanones, the ring-enlarged compounds of the type 4 and 5 were prepared in three steps. Reduction of the NO₂ group with Bu³SnH and azobisisobutyronitrile led in moderate yields to simple β-keto-esters which were quantitatively hydrolyzed and decarboxylated to the ketones of the type 8 and 9 . The interesting fragrances Exaltone® ( 8a ) and (±)-muscone ( 9a ) were prepared in this way in overall yields of 22 and 18%, respectively.     

Kinetics of O·− and O3·− in alkaline aqueous solutions of hydrogen peroxide

The photolysis of strong alkaline (pH>12.7) solutions of H₂O₂ yields O^·−, which in the presence of molecular oxygen forms the ozonide radical ion, O₃^·−. A detailed kinetic study on the reaction mechanisms involved during formation and decay of O₃^·− radical ions in these solutions, in the presence and absence of added O^·−/HO^· scavengers is reported. In order to obtain a complete interpretation of the experimental data, kinetic computer simulations were done using a complete set of reactions. A very good agreement between experimental and computer simulated data is obtained. The following simplified mechanism accounts for the observed first-order decay of O₃^·− in alkaline hydrogen peroxide solutions: O^·− + O₂ → O₃^·− O₃^·− → O^·− + O₂ O^·− + S → OH^· + S → HO^· + HO₂⁻ → O₂^·− + H₂O O^·− + HO₂⁻ → O₂^·− + HO⁻ with S: O^·−/HO^· scavengers. © 1997 John Wiley & Sons, Inc.     

Mild template synthesis of a macrocyclic Cu(II) chelate complex with 1,10-diamino-1,10-dimercapto-5,6-dimethyl-4,7-diazadeca-1,4,6,9-tetraene-3,8-dithione in Cu<Subscript>2</Subscript>[Fe(CN)<Subscript>6</Subscript>]-gelatin-immobilized matrix implantates

Complexation in Cu₂[Fe(CN)₆]-gelatin-immobilized matrix implantates in contact with alkaline (pH > 10) aqueous solutions containing propane-1,3-dithioamide and butane-2,3-dione, as well as with an ethanolic solution containing the same organic compounds, was studied. It was found that room-temperature complexation in the gelatin matrix gives a macrocyclic complex CuL¹with a tetradentate N,S,S,N-donor ligand via a template synthesis, while complexation in solution at room and higher temperatures yields only a bischelate Cu(II) complex with monodeprotonated propane-1,3-dithioamide. Schemes of the complexation processes were proposed. It was demonstrated that when propane-1,3-dithioamide and butane-2,3-dione are in direct contact in solution, the above N,S,S,N-donor ligand was formed in neither the presence nor the absence of Cu²⁺.     

Synthesis and transformations of metallacycles 36. Cycloalumination of macrocyclic diacetylenes with Et<Subscript>3</Subscript>Al catalyzed by Cp<Subscript>2</Subscript>ZrCl<Subscript>2</Subscript>

Cycloalumination of macrocyclic diynes with Et₃Al catalyzed by Cp₂ZrCl₂ resulted in unsaturated bi- and tricyclic mono- and dialuminacarbocycles in 76–91% yields.     

Surface effects on the Formation of Hydrogen Peroxide from dissociated water vapour

The formation of hydrogen peroxide at 77°K from water vapour dissociated in a low-pressure electrodeless discharge was investigated as function of the surface-to-volume ratio. S/V, of both coated and uncoated tubular reactors interposed between the discharge exit and the coolant level. As S/V was increased, the peroxide yield increased to a maximum value and then decreased; this maximum shifted to much lower values of S/V for KCl-coated and H₃PO₄-coated surfaces. Compared with uncoated Pyrex surfaces, H₃PO₄-coatings gave higher H₂0₂ yields whereas KCl-coatings gave lower yields. Surfaces coated well with ice did not show much effect, but condensed water films decreased the H₂O₂ yield. Similar results were obtained when the surface area and the volume traversed by the dissociated vapour were varied at constant S/V. These surface effects are discussed to show that the formation of H₂O₂ occurs via the cold surface reactions H + O₂ → O_aH and H + 0₂H → H₂O₂ and not by the dimerization of OH radicals.     

Synthesis,molecular structure and electrochemistry of pentagonal bipyramidal nickel(II) complexes of quinquedentate macrocylic ligand incorporating a 2,2′:6′,2″-terpyridyl moiety

The synthesis and single crystal X-ray structure of the pentagonal bipyramidal nickel(II) complex [Ni(L)(EtOH)₂](BF₄)₂ involving the quinquedentate terpyridyl macrocyclic ligand L is reported; the electrochemical reduction of such complexes yields, in solution, d⁹ nickel(I) species.     

The constitution of roridin A. Verrucarins and roridins, 11

The antibiotic roridin A (C₂₉H₄₀O₉) yields on base catalysed hydrolysis verrucarol ( 10 ) and roridinic acid ( 13 ) (C₁₄H₂₂O₇), a hitherto unknown dicarboxylic acid whose structure was proved by degradation. In roridin A 10 and 13 are united to form a macrocyclic diester to which structure 1 is assigned.     

Photochemische Reaktionen. 50. Mitteilung [1]. Zur Photochemie von gesättigten β-Ketosulfiden II. Synthese von 6-Hydroxy-2-thia-7-oxa-isotwistan

The results of the ultraviolet irradiation of the saturated β-ketosulfide 2 are discussed. The photochemistry of 2 is characterized by the occurrence of two primary photoprocesses. Their efficiences depend markedly on the excited transition, (charge-transfer)- or (n → π*)-excitation, respectively. In methanol solution (charge-transfer)-excitation leads almost exclusively to product 7 , due to (C_α – S)-fission, and (n → π*)-excitation to nearly equal amounts of 7 and of products 4 and 6 which result from α-cleavage. On solvent sensibilization in benzene products 4, 6, 7 and the still unidentified product 5 ² are formed. Compounds 4 and 6 have been described earlier [2]. The structure elucidation of 7 is reported in this paper. Acid-induced transformation of 7 yields the dihetero-isotwistane 15 .     

Die Konstitution von Roridin D. Verrucarine und Roridine, 12. Mitteilung

The antibiotic roridin D (C₂₉H₃₈O₉), a companion of roridin A, yields on base catalysed hydrolysis verrucarol ( 3 ) and the hitherto unknown 2, 3-epoxy-2-anhydrororidinic acid ( 4 ) (C₁₄H₁₈O₇). Roridin D is a macrocyclic diester to which structure 1 is assigned. In roridin D an epoxy group replaces the hydroxyl group of roridin A.