In situ formation of palladium(0) from a P,C-palladacycle

In DMF at 80 °C, a Pd⁰ complex is generated in situ from the dimeric P,C-palladacycle (1) in the absence of any reducing agents, presumably via a reductive elimination. The Pd⁰ complex formed in an endergonic equilibrium has been trapped and stabilized by an additional P(o-Tol)₃ and has been detected in cyclic voltammetry by its oxidation peak. Its formation is favored by acetate anions (often used as base in Heck reactions) via the formation of a monomeric anionic P,C-palladacycle ligated by acetate ions. As postulated, P,C-palladacycles are a reservoir of monophosphine-Pd⁰ complexes active in oxidative additions with aryl halides.     

Efficient synthesis of benzyl 2-(S)-[(tert-butoxycarbonyl)amino]-ω-iodoalkanoates

The efficient synthesis of four benzyl 2-(S)-[(tert-butoxycarbonyl)amino]-ω-iodoalkanoates {benzyl 2-(S)-[(tert-butoxycarbonyl)amino]-3-iodopropanoate, benzyl 2-(S)-[(tert-butoxycarbonyl)amino]-4-iodobutanoate, benzyl 2-(S)-[(tert-butoxycarbonyl)amino]-5-iodopentanoate, benzyl 2-(S)-[(tert-butoxycarbonyl)amino]-6-iodohexanoate} from natural or protected l-amino acids is described.     

The synthesis and electrochemical behavior of 1,4-di-(2,5-dimethylazaferrocenyl)-1,3-butadiyne

Rigid-rod ferrocene capped alkynes have attracted a lot of attention recently. In this note we report an efficient synthesis of the 1,4-di-(2,5-dimethylazaferrocenyl)-1,3-butadiyne which is the first known azaferrocene capped diacetylene derivative. The cyclic voltammetry measurements at different scan rates and temperatures indicate good electronic communication between two iron centers. Better shaped reduction peaks at higher scan rates in 22 °C and −40 °C can point to increased stability of the monocation.     

A scalable synthesis of (1R,3S,5R)-2-(tert-butoxycarbonyl)-2-azabicyclo[3.1.0]hexane-3-carboxylic acid

A stereoselective and scalable synthesis of (1R,3S,5R)-2-(tert-butoxycarbonyl)-2-azabicyclo[3.1.0]hexane-3-carboxylic acid (3a) is described. Key to the success of the devised route was the realization that the stereoselectivity of a cyclopropanation step could be controlled by the composition of the functional group at C-α.     

Resolution of (4RS,5RS)-4,5-diphenylimidazolidine-2-thione using pentafluorophenyl active esters

(4RS,5RS)-4,5-Diphenylimidazolidine-2-thione is resolved efficiently by treatment with NaHMDS and an enantiomerically pure pentafluorophenyl active ester. The levels of diastereocontrol were excellent (up to 90% de).     

Intermittent simulated moving bed chromatographic separation of (RS,RS)-2-(2,4-difluorophenyl)butane-1,2,3-triol

The pharmaceutically relevant compound (RS,RS)-2-(2,4-difluorophenyl)butane-1,2,3-triol, an important intermediate in the production of different antifungal drugs, is synthesized in racemic form. For further use in the laboratory the compound has to be separated into its pure enantiomers. This work describes the different steps required to set up a chiral separation using intermittent simulated moving bed chromatography (I-SMB). Furthermore, the effect of feed concentration on the choice of the operating conditions is presented in the frame of the triangle theory. The experiments are carried out at increasing total feed concentration ranging from 3 to 15 g/L. The results demonstrate that a successful I-SMB separation could be carried out thus separating 4.5 g of the racemic mixture and fulfilling the specified purity specification of 98% for both enantiomers.     

Reaction of trans-[Pt(H)2(PCy3)2] with C60 reductive elimination of H2 and formation of [Pt(PCy3)2(η-C60)]

Reaction of trans-[Pt(H)₂(PCy₃)₂], 1, with [60]fullerene at room temperature affords [Pt(PCy₃)₂(η²-C₆₀)], 2, in nearly quantitative yield. The most probable reaction pattern is the insertion of a fullerene 6,6 junction onto a Pt-H bond yielding an η¹ alkyl derivative which, after hydrogen extrusion, gives 2. On the other hand, addition of 1 to different electron-deficient olefins, such as dimethyl maleate and fumarate, furnishes mixtures of both η¹ metal—alkyl and η² metal—olefin derivatives. If tetrachloroethylene is used as 2π component, trans-[PtCl(H)(PCy₃)₂] forms exclusively.     

Reductive elimination reaction of rhenium complexes trans-(η-C5Me5)Re(CO)2(chloroaryl)Cl

Thermal reaction of the chloroaryl-chloride complexes trans-(η⁵-C₅Me₅)Re(CO)₂(Ar^Cl)Cl (Ar^Cl = 3-ClC₆H₄, 3-ClC₆H₃(4-Me) and 3,5-Cl₂C₆H₃) in acetonitrile did not interconvert to the cis isomer, instead the complex ReCl(CO)₂(NCMe)₃ and the corresponding 5-Ar^Cl-1,2,3,4,5-pentamethylcyclopentadiene were formed. Similar reductive elimination products were obtained when the starting rhenium complexes were reacted with trimethylphosphite in toluene.     

Efficient synthesis of (Z)- and (E)-methyl 2-(methoxyimino)-2-phenylacetate

Direct oximation of 2-oxo-2-phenylacetate (3) gave the (Z)-methyl 2-(methoxyimino)-2-phenylacetate (1) in 71% yield, while the E oxime 2 was prepared from 3 in 65% yield via oxime isomerization of 2-(methoxyimino)-2-phenylacetic acid (5). Computational studies suggest that the isomerization of 5 is thermodynamically driven, while the direct oximation of ketoester 3 is kinetically controlled.     

On the electrochemical behaviour of 5(1H)-pyrromethenones and 3,4-dihydro-5(1H)-pyrromethenones

Cyclic voltammetry and polarography measurements in anhydrous dimethylformamide indicate that 1,3,4,5-tetrahydro-3-methoxycarbonylmethyl-3,4,4,4-tetramethyl-5-oxo-2,2-pyrromethen-5-carboxylic acidtert-butylester [a 3,4-dihydro-5(1H)-pyrromethenone] is both easier to reduce and to oxidize than structurally related 5(1H)-pyrromethenones.

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Notiz über das elektrochemische Verhalten von 5(1H)-Pyrromethenonen und 3,4-Dihydro-5(1H)-pyrromethenonen (Kurze Mitteilung)

Zusammenfassung Cyclische Voltammetrie und Polarographie in wasserfreiem Dimethylformamid haben gezeigt, daß 1,3,4,5-Tetrahydro-3-methoxycarbonylmethyl-3,4,4,4-tetramethyl-5-oxo-2,2-pyrromethen-5-carbonsäure-tert-butylester sowohl leichter zu reduzieren als auch zu oxidieren ist als 5(1H)-Pyrromethenone mit ähnlicher Struktur.

     

Intramolecular reductive amination strategy to the synthesis of (R)-N-Boc-2-hydroxymethylmorpholine, N-(3,4-dichlorobenzyl)(R)-2-hydroxymethylmorpholine, and (R)-2-benzylmorpholine

A concise high yielding enantioselective synthesis of (R)-N-Boc-2-hydroxymethylmorpholine, N-(3,4-dichlorobenzyl)(R)-2-hydroxymethylmorpholine, and (R)-benzylmorpholine has been achieved by employing proline-catalyzed asymmetric α-aminooxylation of aldehyde and palladium-catalyzed intramolecular reductive amination of azido aldehyde as the key steps.     

FTIR spectroscopy study of the electrochemical reduction of CO2 on various metal electrodes in methanol

The electrochemical reduction of CO₂ on Sn, Cu, Au, In, Ni, Ru and Pt electrodes in methanol containing 0.1 M sodium perchlorate was studied by cyclic voltammetry and in-situ FTIR spectroscopy. Dissolved CO₂ increases the cathodic current at potentials below −1.3 V vs. Ag|0.01 M Ag⁺ with Sn, Au, Cu, In and Ni electrodes. It is concluded from the FTIR spectra obtained that there is no reduction of CO₂ on any of the metals studied, and that the only reaction product detected by Fourier transform (FT) IR spectroscopy, i.e. CO²⁻₃, is formed by reaction of CO₂ with hydroxyl anions produced in the electroreduction of residual water.In order to identify the electroreduction products of CO₂ it was necessary to obtain the FTIR spectra of sodium oxalate and sodium carbonate in methanol. They were obtained by the electroreduction of oxalic acid and the alkalinization of CO₂-saturated methanol respectively. It could be proved that the electroreduction of carboxylic acids to carboxylate anions in organic solvents does not require either a H-chemisorbing metal electrode, or the presence of water in the solvent.     

Synthesis, photochemical, and electrochemical properties of naphthalene-1,4,5,8-tetracarboxylic acid-bis-(N,N′-bis-(2,2,4(2,4,4)-trimethylhexylpolyimide)) and poly(N,N′-bis-(2,2,4(2,4,4)-trimethyl-6-aminohexyl) 3,4,9,10-perylenetetracarboxdiimide)

Two new soluble polymers (naphthalene containing: TH-NPI, perylene containing: TH-PPI) have been synthesized via incorporation of branched chain substituent unit into their backbones. Because of existence of branched alkyl spacer, the polymers showed good solubility in common solvents such as chloroform without sacrificing their stability and caused a red shifted excimer-like emission. Their monomers (TH-NDI and TH-PDI) have been synthesized for comparison. The compounds are characterized by UV-vis, IR, MS, DSC, TGA, CV, GPC and viscosity measurements. Polymers TH-NPI and TH-PPI with inherent viscosities of 0.50 and 0.30 dL/g were obtained corresponding to their molecular weights 40,000 and 17,000 respectively. Thermogravimetric analysis (TGA) showed that TH-NDI, TH-NPI, TH-PDI and TH-PPI are thermally stable up to 380, 445, 512 and 515 °C respectively. The LUMO energy levels of these compounds are calculated as −3.66, −3.71, −3.62 and −3.61 eV respectively. The red-shifted (TH-NPI: 400-650 nm, TH-PPI: 535-800) excimer-like fluorescence in chloroform is attributed to the formation of ground state complexes probably due to intermolecular and intramolecular π-stackings of the polymers in solution. The fluorescence lifetimes, quantum yields and singlet-state energies are presented.     

Racemic [1SR,2RS,(RS)]-N-cyano(phenyl)methyl-1-aminoindan-2-ol: crystal structure and reactivity towards thermal epimerization in the solid state

A diastereomeric mixture of racemic α-amino nitriles [1SR,2RS,(SR)]- (1) and [1SR,2RS,(RS)]-N-cyano(phenyl)methyl-1-aminoindan-2-ol (2) was thermally epimerized in the solid state to give diastereopure [1SR,2RS,(SR)]-1. The reaction was about 26 times slower than the same reaction of a mixture of their enantiopure counterparts, showing that different mechanisms operated between the two transformations. X-ray crystallographic analysis revealed that in the former transformation, racemic-compound crystals of 2 were converted into conglomerate crystals of 1, while in the latter, enantiomeric crystals of 2 were converted into enantiomeric crystals of 1. The difference in the reactivity toward the epimerization between the racemic and the enantiopure mixture could be rationalized by the difference in the stability of compound 2 in the two crystal forms.     

An unusual behaviour of N-(tert-butoxycarbonyl)- and N-pivaloyl-(methylthio)anilines in metallation reactions

The metallation reaction of N-Boc-and N-Piv-(methylthio)anilines are here described. The results show that N-Boc derivatives are metallated only by superbases to give products substituted at the thiomethylic group. N-Piv derivatives show a different behaviour: ortho-derivative is metallated by both butyllithium and superbase at the thiomethylic carbon atom, while para-derivative is metallated in ortho to the N-Piv group by butyllithium and at the thiomethylic carbon atom by superbase. The meta-derivative is metallated only by superbase at the thiomethylic carbon atom.     

Stereoselective synthesis of (E)- and (Z)-3-hydroxy-2-methyl-1-alkenyl iodides by base-promoted ring-opening of iodomethylated epoxides

Both (E)- and (Z)-3-hydroxy-2-methyl-1-alkenyl iodides were stereoselectively synthesized from iodomethylated epoxides by treatment with sodium hexamethyldisilazane in DMF and with LDA in THF (or lithium 2,2,6,6-tetramethylpiperidide in THF), respectively.     

Lipase-mediated kinetic resolution of (RS)-1-bromo-3-[4-(2-methoxy-ethyl)-phenoxy]-propan-2-ol to (R)-1-bromo-3-(4-(2-methoxyethyl) phenoxy) propan-2-yl acetate

A novel biocatalytic method for the enantioselective synthesis of (R)-bromo-3-[4-(2-methoxy-ethyl) phenoxy]-2-propanol [(R)-BMEPP], a precursor for the synthesis of (S)-metoprolol, an anti hypertensive drug is described. We have developed kinetic resolution of rac-BMEPP by transesterification using Candida rugosa lipase and vinyl acetate as the acyl donor affording the product with excellent conversion (49%) and ee (>99%). Various reaction parameters (source of enzyme, reaction media, and concentration of substrate and acylating agent) for the enzymatic kinetic resolution have been reported.     

Synthesis,electrochemical, in situ spectroelectrochemical and in situ electrocolorimetric characterization of new metal-free and metallophthalocyanines substituted with 4-{2-[2-(1-naphthyloxy)ethoxy]ethoxy} groups

The synthesis of novel metal-free and metallophthalocyanines [Ni(II), Zn(II), Co(II), Cu(II)] were prepared by cyclotetramerization of a novel 4-{2-[2-(1-naphthyloxy)ethoxy]ethoxy}phthalonitrile and the corresponding metal salts (NiCl₂, Zn(CH₃COO)₂, CoCl₂ and CuCl₂). The structures of the target compounds were confirmed using elemental analysis, IR, ¹H NMR, ¹³C NMR, UV–Vis and MS spectral data. Voltammetric and in situ spectroelectrochemical measurements show that while cobalt phthalocyanine complex gives both metal-based and ring-based redox processes, metal-free, and zinc phthalocyanines show only ring-based reduction and oxidation processes. All complexes decomposed and coated on the electrode as nonconductive film at positive potential window of the electrolyte. An in situ electrocolorimetric method has been applied to investigate color of the electro-generated anionic and cationic forms of the complexes.