Chiral (salen)Co(III) catalyst for the synthesis of cyclic carbonates

A catalyst system comprised of a Co(III)(salen) complex and a Lewis base is investigated for the reaction of CO2 and a variety of epoxides to form cyclic carbonates. Application of this catalyst system in the kinetic resolution of propylene oxide is also discussed.     

An efficient procedure for the preparation of (E)-alpha-alkylidenecycloalkanones mediated by a CeCl(3) x 7H(2)O-NaI system. Novel methodology for the synthesis of (S)-(-)-pulegone

2-Alkylidenecycloalkanones are powerful synthons used as the key intermediates in many important syntheses. Because of their potential, a general method of preparation from readily available starting materials, under very mild conditions, was considered to be worthwhile. Cerium(III) chloride heptahydrate in combination with sodium iodide in refluxing acetonitrile promotes a regio- and stereoselective beta-elimination reaction to (E)-2-alkylidenecycloalkanones in 2-(1-hydroxyalkyl)cycloalkanones. The synthetic value of the present procedure is demonstrated by the synthesis of monoterpene (S)-(-)-pulegone (8) in its optically active form.     

A method for the synthesis of nickel(0) bis(carbene) complexes

A new method leading to Ni(NHC)2 (NHC = IMes, IPri, SIPr(i), SIBu(t)) complexes in moderate to good yields, involves the reaction of NHC (pre-formed or generated in situ) with Ni(CH3)2(tmed), tmed = N,N'-tetramethylethylenediamine; in one case, the intermediate Ni[I(Me2)Pr(i)]2(CH3)2, I(Me2)Pr(i) = N,N'-diisopropyl-4,5-dimethylimidazol-2-ylidene, has been isolated and structurally characterised.     

Method for the determination of chromium (VI) as chromium (VI)-dibenzyidithiocarbamate

Dibenzyldithiocarbamic acid (DBDC) exhibits the ability to speciate between chromium(VI) and chromium(III), since only the chromium(VI) will form complexes with DBDC. The complex is then extracted into an organic solvent and assayed using an ultraviolet-visible (UV-VIS) spectrophotometer at 498.8 nm. Using 250 ml of aqueous sample detection limits less than 1 ng/ml are possible, while the linear range extends to 500 gmg/ml when working at 498.8 nm. Oxidation of the chromium(III) to chromium (VI) using cerium (IV) enables the determination of total chromium and subsequently the chromium (III) in solution. Evaluation of the method with a standard reference material produced only 4.81 part per thousand error in the determination of chromium(VI).     

Analysis of the spin lattice model for the spin-gapped layered compounds Na(3)Cu(2)SbO(6) and Na(2)Cu(2)TeO(6) on the basis of electronic structure calculations

The spin lattice model for the spin-gapped layered magnetic solids Na3Cu2SbO6 and Na2Cu2TeO6 was examined by evaluating the three spin exchange interactions of their Cu2MO6 (M = Sb, Te) layers in terms of spin dimer analysis based on extended Hückel tight binding calculations and mapping analysis based on first principles density functional theory electronic band structure calculations. For both compounds, our calculations show that the two strongest spin exchange interactions, that is, the Cu-O...O-Cu super-superexchange (J2) and the Cu-O-Cu superexchange (J1) interactions, form alternating chains that interact weakly through the Cu-O-Cu superexchange (J3) interactions. The dominant one of the three spin exchange interactions is J2, and it is antiferromagnetic in agreement with the fact that both of the compounds are spin gapped. For Na3Cu2SbO6 and Na2Cu2TeO6, the superexchange J1 is calculated to be ferromagnetic, hence, leading to the alternating chain model in which antiferromagnetic and ferromagnetic spin exchange interactions alternate. This picture does not agree with the recent experimental analysis, which showed that the temperature-dependent magnetic susceptibilities of both compounds should be described by the alternating chain model in which two antiferromagnetic spin exchange interactions of different strengths alternate.     

Methods for the synthesis of haloimidazoles (review)

Published information on methods for the synthesis of haloimidazoles is summarized and classified.     

Methods for the synthesis of cinnolines (review)

This review analyses the principal approaches to the synthesis of the cinnoline nucleus, used as synthetic precursors of arenediazonium salts, arylhydrazones, and arylhydrazines, and also reductive methods for the synthesis of polycondensed derivatives of cinnoline. The mechanisms of the transformations and the possibilities and limitations of the various methods are discussed. Special attention is paid to methods based on the cyclization of derivatives of arenediazonium salts, which have been developed substantially in recent years. In memory of A. A. Potekhin __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 643–667, May, 2008.     

Sequential Pd(II)-Pd(0) catalysis for the rapid synthesis of coumarins

Electrophilic palladium-catalyzed cycloisomerization of brominated aryl propiolates produces brominated coumarins. The brominated coumarins can be diversified by reduction of the Pd(II) catalyst to Pd(0) followed by Suzuki, Sonogashira, Heck, or Hartwig-Buchwald coupling. Thus, a single loading of precatalyst can be used to conduct sequential reactions, allowing the synthesis of functionalized coumarins. Extension of this methodology toward the synthesis of coumarin libraries is discussed.     

Poly(difluorophosphazene): A New Intermediate for the Synthesis of Poly(organophosphazenes)

Although many poly(organophosphazenes) have been synthesized, new preparative pathways are needed, especially for polymers that contain alkyl side groups. A new development involves the use of poly(difluorophosphazene), (NPC1₂) instead of poly-(dichlorophosphazene), (NPC1²)_n, as a substrate for reactions with organometallic reagents. This approach has allowed the preparation of a new class of poly(organophosphazenes) that possess substituent groups linked to the skeleton through direct phosphorus-carbon bonds. The synthesis of uncrosslinked poly-(difluorophosphazene) and its reactions with alkoxides and amines are also reviewed.     

New chemo-enzymatic approaches for the synthesis of (R)- and (S)-bufuralol

Both enantiomers of bufuralol are pharmaceutically important molecules. While the (S)-isomer with a higher β-blocking activity is recommended for hypertension treatment, the (R)-enantiomer can be used as marker of hepatic activity. In this paper two new alternative approaches are described for their chemo-enzymatic synthesis, providing both highly enantiomerically enriched stereoisomers of the target molecule (ee 96–98%). One route is based on the baker’s yeast mediated stereoselective biotransformation of α-substituted ketones, and the other one on the lipase mediated kinetic resolution of the racemic bromoethanol.     

Evaluation of the photocurrent value for poly(2,5-dicyano- p -phenylene-vinylene)-co-(p-phenylene-vinylene) (DCN-PPV/PPV)

Journal of Solid State Electrochemistry - A method to obtain poly(2,5-dicyano-p-phenylene-vinylene)-co-(p-phenylene-vinylene) (DCN-PPV/PPV) block copolymer was developed. The structural...     

The importance of the ene reaction for the C(2)-C(6) cyclization of enyne-allenes

The present study establishes the ene reaction as a competing reaction mechanism to the diradical mechanism for the thermal C(2)-C(6) cyclization of enyne-allenes which possess bulky substituents at the alkyne terminus. Both reaction routes are found to possess nearly equal free energies of activation. As shown by our computations, primary H/D isotope effects could be used for a definite decision about the mechanism. Concerning the regioselectivity of the cyclization reactions of enyne-allenes our study resolves a long-standing deviation between theoretical results and experimental findings.     

The Solubility of Bis(cyclopentadienyl)samarium(II) and Implications for the Reaction of Samarium Metal with Bis(cyclopentadienyl)mercury(II)

Bis(cyclopentadienyl)samarium(II) has been shown to be insoluble in thf : ether mixtures, hence it cannot be isolated as a soluble product from the reaction of samarium with HgCp₂ in thf : ether.     

2-(2-Thiazolylazo)-p-cresol(TAC) as a Reagent for the Spectrophotometric Determination of Lead(II)

Abstract

The reaction between lead(II) and 2-(2-Thiazolylazo)-p-Cresol(TAC) in the presence of TERGITOL NPX (4 mg/ml) at an apparent pH 9.0–10.0 results in an intensely colored complex which is stable for at least 4 hr.

The composition of the complex is 1:2 cation: TAC and the log of the formation constant is 11.92 ± 0. 40. Beer's law is obeyed up to 6.0μg.ml^?1 of lead(II) at 650nm.

The apparent molar absorptivity at 650 nm is 2.07 × 10⁴ 1. mole^?1.cm^?1 and the detection limit was obtained as 10.0 ng.ml^?1 of lead(II).

The method is applied to determination of lead(II) in copper-base alloy.     

2-(2-Thiazolylazo)-pcresol (TAC) as a reagent for the spectrophotometric determination of titanium (IV)

The reaction between titanium(IV) and 2-(2-thiazolylazo)-p-cresol-(TAC) in aqueous methanol media at apparent pH 4.0–5.6 results in a intensely coloured complex that is stable for at least 2 h. The combining ratio is 1 1 cation TAC. Beer's law is obeyed up to 5.0 g/ml titanium(IV) at 580 nm. The apparent molar absorptivity at 580 nm is 9.82.10³ l.mole^–1.cm^–1 and the detection limit obtained was 5 ng/ml titanium (IV). A spectrophotometric method for the simultaneous determination of titanium and iron with TAC is proposed.