Direct Mannich reaction mediated by Fe(Cp)2PF6 under solvent-free conditions

Fe(Cp)₂PF₆ (5 mol %) efficiently catalyzed Mannich reaction of aldehydes, anilines, and ketones under solvent-free condition to give β-amino-ketones in high yield (up to 94%) within 30 min with anti-isomer in excess. Simple experimental conditions and product isolation procedure makes this protocol potential for the development of clean and environment-friendly strategy for the synthesis of β-amino-ketones.     

Binuclear Cu(II) chiral complexes: synthesis,characterization and application in enantioselective nitroaldol (Henry) reaction

Enantiopure macrocyclic ligands were synthesized from (1R,2R)‐(+)‐ and (1S,2S)‐(?)‐diphenylethylenediamine with 3,3'‐methylenebis(5‐(tert‐butyl)‐2‐hydroxybenzaldehyde) and characterized. The chirality transfer and chiral inversion from ligand to copper(II) metal centre were studied using circular dichroism spectroscopy. The enantiopure binuclear copper(II) complexes (ΔΔ and ΛΛ) were used as catalysts for asymmetric nitroaldol reaction to generate β‐nitroalcohol with 88% yield and 67% enantioselectivity. Copyright © 2015 John Wiley & Sons, Ltd.     

Carbon stable isotopes reveal complex trophic interactions in lake plankton

The lower trophic linkages in lake plankton food webs are generally described as relatively simple, even accounting for the additional complexity of potential 'microbial looping'. Crustacean zooplankton are frequently amalgamated into one trophic functional group as grazers of autotrophic production. The carbon stable isotope ratios for separated zooplankton species, particulate organic matter (POM) and phytoplankton from a number of lakes in Finland and the UK were analysed. These revealed greater complexity in trophic interactions than would otherwise be observed if the zooplankton had been represented by a mixed sample. Grazing zooplankton were usually depleted in (13)C relative to the bulk POM on which they might feed, with (13)C deviating by up to 17 per thousand There were no consistent differences between (13)C values for copepods and cladocerans. Predatory cladocerans were generally enriched by greater than 1 per thousand compared to their putative prey. We suggest that care in separating the zooplankton species for stable isotope analysis may expose otherwise undetected sources of carbon and facilitate unravelling trophic links further up the food web. Copyright 1999 John Wiley & Sons, Ltd.     

Enantioselective epoxidation reaction of non-functionalised prochiral alkenes using optically resolved [brucine](R)-[Ru(PDTA-H)Cl] and [brucine](S)-[Ru(PDTA-H)Cl] complexes

The racemic metal complex K[Ru(PDTA-H)Cl]¹ has been resolved into its optical isomers using brucine as the resolving agent counter ion, [brucine](S)-[Ru(PDTA-H)Cl] (1) and [brucine](R)-[Ru(PDTA-H)Cl] (2) and their structures are determined by single crystal X-ray methods. Longer Ru–Cl bonds in both the complexes (2.3974(13)A in 1 and 2.415(6) in 2 along with one relatively weaker and strained chelation ring could be responsible for their catalytic activity. The CD pattern of the complex 1 shows the presence of the two isomers λ and δ with more contribution of λ form while the complex 2 acquire only λ conformation. Catalytic activity of 1 and 2 for enantioselective epoxidation of non-functionalised alkenes viz. styrene, 4-chloro-, 4-methyl-, 4-nitrostyrene, 1,2-dihydronaphthalene and indene was accomplished by using molecular oxygen and iodosyl benzene as terminal oxidant. Excellent conversions (85–89%) were obtained in case of 1,2-dihydronaphthalene with both the catalysts while catalyst 2 gave good conversion with styrene and 4-methylstyrene. The enantiomeric excess of the epoxide was determined by ¹H NMR using chiral shift reagent Eu(hfc)₃/ by chiral capillary column. The extent of enantioselectivity with respect to the substituents on substrate is shown on Hammet plot. A possible mechanism at the oxo transfer stage is also envisaged.     

Synthesis,spectroscopic and electrochemical studies of mixed ligand ruthenium(II) chiral Schiff base complexes with nitrogen donors

Summary Mixed ligand complexes (1)-(18) of composition [RuL-(PPh₃)Y] and [RuL(PPh₃)(H₂O)Y]^- (L = chiral Schiff bases derived from l-alanine, l-valine, l-serine, l-cystein, l-arginine or l-aspartic acid with salicylaldehyde; Y = azide, 2,2-bipyridyl or 1,10-phenanthroline) have been prepared and characterized by microanalysis, spectroscopy and polarography. The conformational aspects regarding the relationship of the asymmetric carbon atom to the nitrogen donors around the Ru^II are discussed. All complexes showed quasi-reversible c.v. behaviour and the redox potentials of the Ru^II/Ru^I couple lie in the -0.31 to-0.16 V range.     

Mn(III) salen complexes-catalyzed enantioselective addition of trimethyl silylcyanide to N-benzylimines in the presence of 4-phenyl pyridine-N-oxide as an additive

Chiral monomeric and dimeric Mn(III) salen complexes viz., [(S,S)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminato manganese(III) chloride and 5,5-methylene di-[(S,S)-{N-(3-tert-butyl salicylidine)-N′-(3′,5′-di-tert-butyl salicylidene)}-1,2-cyclohexanediaminato manganese(III) chloride were used as catalysts for the highly enantioselective Strecker reaction of various imines (derived by the condensation of aldehydes and amine) with TMSCN as a source of cyanide in toluene. Excellent yield (95%) of α-amino nitrile with ee >99% was achieved when N-(2-methoxybenzylidine)-1-phenylmethanamine was used as a substrate and 4-phenyl pyridine-N-oxide (4-PPNO) as an additive at ?55 °C in 28 h. The dimeric catalyst was found to be more reactive and enantioselective than the monomeric catalyst. The chiral dimeric catalyst used in the present study was recoverable and recyclable several times with retention of its performance.     

Chiral Ni(II) Schiff base complex-catalysed enantioselective epoxidation of prochiral non-functionalised alkenes

The synthesis, characterisation and single crystal X-ray structures of square planar Ni(II) chiral Schiff base complexes with N₂O₂-type ligands have been described. These catalysts were used for enantioselective epoxidation of non-functionalised alkenes viz. 1-hexene, 1-octene, styrene, 4-chloro-, 4-nitrostyrene and 1,2-dihydronaphthalene using NaOCl as oxidant, giving excellent conversions with long chain alkenes while ee's were moderate to good. A mechanism for the Ni(II)-catalysed epoxidation with NaOCl is proposed.     

Boundedness of Commutators of θ-Type Calderόn-Zygmund Operators on Non-homogeneous Metric Measure Spaces

Let(X, d, μ) be a metric measure space satisfying both the upper doubling and the geometrically doubling conditions in the sense of Hyt?nen. In this paper, the authors obtain the boundedness of the commutators of θ-type Calderón-Zygmund operators with RBMO functions from L~∞(μ) into RBMO(μ) and from H_(at)~(1,∞)(μ) into L~1(μ), respectively.As a consequence of these results, they establish the L~p(μ) boundedness of the commutators on the non-homogeneous metric spaces.     

Synthesis, physico-chemical studies and solvent-dependent enantioselective epoxidation of 1,2-dihydronaphthalene catalysed by chiral Ruthenium(II) Schiff base complexes. I

Ruthenium(II) chiral Schiff base complexes 1–10 and their precursor ligands derived from -amino acids viz. -leucine, -histidine with salicylaldehyde, 3-tertiary-butyl-, 3,5-di-tertiary-butyl-, 3,5 dichloro- and 3,5-dinitrosalicylaldehyde are reported. The characterization of the ligands and complexes was accomplished by various appropriate physico-chemical studies, namely, microanalysis, IR-, UV/Vis-, ¹H, ³¹P{¹H} NMR, CD spectroscopy, optical rotation, conductance measurement and cyclic voltammetry. The complexes thus synthesised were used as catalysts for enantioselective epoxidation of 1,2-dihydronaphthalene. The effect on enantioselectivity and chemical conversions to epoxide were studied in different solvents viz. acetonitrile, dichloromethane and fluorobenzene along with change of the substituents on ligands and different terminal oxidants. The less polar nature of solvent as well as the donating group attached on the catalysts favours enantioselectivity, while PhIO was the oxidant of choice. The enantiomeric excess of the resulting epoxide was evaluated by chiral cyclodex BDA capillary column.     

Asymmetric Hydrolytic Kinetic Resolution with Recyclable Macrocyclic CoIII–Salen Complexes: A Practical Strategy in the Preparation of (R)‐Mexiletine and (S)‐Propranolol

A chiral cobalt(III) complex ( 1 e ) was synthesized by the interaction of cobalt(II) acetate and ferrocenium hexafluorophosphate with a chiral dinuclear macrocyclic salen ligand that was derived from 1R,2R‐(?)‐1,2‐diaminocyclohexane with trigol bis‐aldehyde. A variety of epoxides and glycidyl ethers were suitable substrates for the reaction with water in the presence of chiral macrocyclic salen complex 1 e at room temperature to afford chiral epoxides and diols by hydrolytic kinetic resolution (HKR). Excellent yields (47 % with respect to the epoxides, 53 % with respect to the diols) and high enantioselectivity (ee>99 % for the epoxides, up to 96 % for the diols) were achieved in 2.5–16 h. The Co^III macrocyclic salen complex ( 1 e ) maintained its performance on a multigram scale and was expediently recycled a number of times. We further extended our study of chiral epoxides that were synthesized by using HKR to the synthesis of chiral drug molecules (R)‐mexiletine and (S)‐propranolol.