Reaction of polyperoxides with triphenylphosphine

The triphenylphosphine deoxygenation of the polyperoxides, poly(styrene peroxide), poly(methyl methacrylate peroxide), and poly(alpha-methylstyrene peroxide) proceed via the phosphorane intermediates, which in the presence of moisture hydrolyze to give the respective diols. At higher temperatures and under dry conditions the phosphorane decomposes into epoxide and triphenylphosphine oxide. The reaction has been studied by H-1-, C-13-, and P-31-NMR spectroscopy. The results obtained are consistent with a concerted insertion of the biphile, triphenylphosphine, into the peroxy bond and this reaction pathway seems to be new as far as the chemistry of polyperoxides is concerned. Though the aim of this investigation was to test the selective deoxygenation of polyperoxide by triphenylphosphine as a method of preparing polyethers, it turned out to be a fruitful method of synthesis of stereospecific diols. (C) 1997 John Wiley & Sons, Inc.

Reactivity of some tetra substituted furans and thiophenes towards BF3-Et(2)O catalysed Diels-Alder reaction

Some tetra substituted furans and thiophenes were reacted with methyl acrylate under BF3-etherate catalysed Diels-Alder conditions. While the derivatives of furan underwent Diels-Alder reaction in a facile manner, an observation of 2,5-dimethyl-3,4-dianisylthiophene undergoing Diels-Alder reaction with methyl acrylate is remarkable. (C) 1997, Elsevier Science Ltd.

Studies of moisture induced crosslinking in a novel vinyl ether maleic anhydride copolymer

A novel vinyl ether, 2,2-dimethyl-4-vinyioxymethyl-1,3-dioxol (DMVMD), that has a dimethyl ketal protected vicinal diol functionality was synthesizied from readily available starting materials, such as glycerol, acetone and acetylene. Copolymerisation of DMVMD with maleic anhydride (MAH) in various molar ratios was carried out using a free radical initiator. The composition of the copolymer was established by conductometric titration, and was found to be 1:1 irrespective of the monomer feed composition thus establishing its alternating nature. The copolymer formed clear free standing films upon solvent casting which became insoluble upon prolonged exposure to ambeint atmosphere. The insolubility is ascribed to moisture induced crosslinking. A plausible mechanism for the crosslinking involves the hydrolysis of some of the anhydride groups, followed by acid catalysed deketalization, and then by the reaction of the alcoholic groups, thus generated, with the residual anhydride to give ester crosslinks. This hypothesis was confirmed both by model reactions and insitu FT-IR studies.

Interesting reaction of 2,2 '-binaphthol with 1,2-dibromoethane: Synthesis of a novel spirodienone

2,2'-Binaphthol 1 reacts with 1,2 dibromoethane in the presence of potassium carbonate to give rise to a novel spirodienone system 3 and its structure has been confirmed by X-ray analysis.

Ultrafast Microwave-Assisted Route to Surfactant-Free Ultrafine Pt Nanoparticles on Graphene: Synergistic Co-reduction Mechanism and High Catalytic Activity

We demonstrate an ultrafast method for the formation of, graphene supported Pt catalysts by the co-reduction of graphene oxide and Pt salt using ethylene glycol under microwave irradiation conditions. Detailed analysis of the mechanism of formation of the hybrids indicates a synergistic co-reduction mechanism whereby the presence of the Pt ions leads to a faster reduction of GO and the presence of the defect sites on the reduced GO serves as anchor points for the heterogeneous nucleation of Pt. The resulting hybrid consists of ultrafine nanoparticles of Pt uniformly distributed on the reduced GO susbtrate. We have shown that the hybrid exhibits good catalytic activity for methanol oxidation and hydrogen conversion reactions. The mechanism is general and applicable for the synthesis of other multifunctional hybrids based on graphene.

Regioselective synthesis of bicyclo[4.2.1]nonane-2,8-diones via BF3.Et2O mediated intramolecular diazo ketone insertion reaction

Treatment of the diazo diones 11a-d with boron trifluoride diethyl etherate furnished the bicyclo[4.2.1]nonane-2,g-diones 15a-d in a highly regioselective manner. (C) 1999 Elsevier Science Ltd. All rights reserved.

Synthesis of chiral bicyclo[4.3.1]decanes via an intramolecular carbonyl ene-reaction

Synthesis of chiral bicyclo[4.3.1]decanes via an intramolecular acid catalysed type II ene reaction of chiral (5-isopropenylcyclohex-2-enyl)acetaldehydes derived from (R)-carvone is described. (C) 1999 Elsevier Science Ltd. All rights reserved.

Chemistry of dihydrogen complexes containing only phosphorus co-ligands

A series of new dicationic dihydrogen complexes of ruthenium of the type cis-[(dppm)(2)Ru(eta(2)-H-2)(L)][BF4](2) (dppm = Ph2PCH2PPh2; L = phosphite) have been prepared by protonating the precursor hydride complexes cis-[(dPPM)(2)Ru(H)(L)][BF4] using HBF4.Et2O. The precursor hydride complexes have been obtained from trans-[(dppm)(2)Ru(H)(L)][BF4][(L = phospfiite) via a rare acid-catalysed isomerization reaction in six coordinate species. The trans-[(dppm)(2)Ru(H)(L)][BF4] complexes (L = phosphine) upon protonation gave the isomerized derivatives, however, further addition of acid resulted in a five-coordinate species, [(dppm)(2)RuCl](+) presumably via an intermediate phosphine dihydrogen complex. The electronic as well as the steric properties of the co-ligands seem to strongly influence the structure-reactivity behaviour of this series of complexes.

Chemistry of tetrathiomolybdate: Applications in organic synthesis

The utility of tetrathiomolybdate in a variety of organic transformations is presented in this account. The sulfur transfer ability of tetrathiomolybdate is exploited in the synthesis of organic disulfides under mild reaction conditions. The induced internal redox reactions associated with tetrathiomolybdate have been thoroughly exploited in developing various methodologies, which include the reduction of organic azides, synthesis of diselenides, cyclic imines, thioamides, and thiolactams. In addition, novel deprotection strategies using tetrathiomolybdate have been developed to cleave the propargyl and propargyloxy carbonyl (POC) protecting groups. Tetrathiomolybdate mediated tandem sulfur transfer-reduction-Michael reactions have been applied to the synthesis of sulfur containing bicyclic systems. Furthermore, the reactions in the solid state and the reactions in water medium assisted by tetrathiomolybdate have greatly simplified the synthesis of organic disulfides.

Direct and sensitized (energy and electron transfer) geometric isomerization of stilbene within zeolites: a comparison between solution and zeolite as reaction media

The trans- and cis-stilbenes upon inclusion in NaY zeolite are thermally stable. Direct excitation and triplet sensitization results in geometric isomerization and the excited state behavior under these conditions are similar to that in solution. Upon direct excitation, a photostationary state consisting of 65% cis and 35% trans isomers is established. Triplet sensitization with 2-acetonaphthone gave a photostationary state consisting of 63% cis and 37% trans isomers. These numbers are similar to the ones obtained in solution. Thus, the presence of cations and the confined space within the zeolite have very little influence on the overall chemistry during direct and triplet sensitization. However, upon electron transfer sensitization with N-methylacridinium (NMA) as the sensitizer within NaY, isomerization from cis-stilbene radical cation to trans-stilbene occurs and the recombination of radical ions results in triplet stilbene. Prolonged irradiation gave a photostationary state (65% cis and 35% trans) similar to triplet sensitization. This behavior is unique to the zeolite and does not take place in solution. Steady state fluorescence measurements showed that the majority of stilbene molecules are close to the N-methylacridinium sensitizer. Diffuse reflectance flash photolysis studies established that independent of the isomer being sensitized only trans radical cation is formed. Triplet stilbene is believed to be generated via recombination of stilbene radical cation and sensitizer radical anion. One should be careful in using acidic HY zeolite as a medium for photoisomerization of stilbenes. In our hands, in these acidic zeolites isomerization dominated the photoisomerization. (C) 2002 Elsevier Science B.V. All rights reserved.

The reaction of aspirin with base

Aspirin anion appears to exist only fleetingly, rearranging via acetyl transfer to the ortho carboxylate group, as indicated by IR, UV and NMR. The resulting mixed anhydride cyclises to the more stable bicyclic orthoacetate isomer, a process facilitated by time and increasing pH. Mechanistic possibilities are discussed to explain these intriguing observations. (C) 2011 Elsevier Ltd. All rights reserved.

Kinetics of hydrogen evolution on submicron size Co, Ni, Pd and CoNi alloy powder electrodes by d.c. polarization and a.c. impedance studies

Submicron size Co, Ni and Co-Ni alloy powders have been synthesized by the polyol method using the corresponding metal malonates and Pd powder by reduction of PdOx in methanol. The kinetics of the hydrogen evolution reaction ( HER) in 6 M KOH electrolyte have been studied on electrodes made from the pressed powders. The d.c. polarization measurements have resulted in a value close to 120 mV decade(-1) for the Tafel slope, suggesting that the HER follows the Volmer-Heyrovsky mechanism. The values of exchange current density (i(o)) are in the range 1-10 mA cm(-2) for electrodes fabricated in the study. The a.c. impedance spectra measured at several potentials in the HER region showed a single semicircle in the Nyquist plots. Exchange current density (i(o)) and energy transfer coefficient (alpha) have been calculated by employing a nonlinear least square-fitting program.

Organometallic chemistry of diphosphazanes. Part 15. Half-sandwich cyclopentadienyl ruthenium complexes of achiral and chiral diphosphazanes

Reaction of [CpRu(PPh3)(2)Cl] (1) {Cp = eta(5)-(C5H5)} with X2PN(CHMe2) PYY' {X = Y = Y' = Ph (L-1); X = Y = Ph, Y' = OC6H4Me-4 (L-4); X = Y = Ph, Y' = OC6H3Me2- 3,5 (L-5); X = Y = Ph, Y' = N2C3HMe2 (L-6)} yields the cationic chelate complexes, [CpRu(eta(2)-(X2PN(CHMe2) PYY')) PPh3] Cl. On the other hand, the reaction of 1 with X2PN(CHMe2)PYY' {X = Ph, YY' = O2C6H4(L-3)} gives the complex, [CpRu(eta(1)-L-2)(2)PPh3] Cl. Both types of complexes are formed with X2PN(CHMe2) PYY' {X = Ph, YY' = O2C6H4 (L-3)}. The reaction of 1 with (R),(S)-(H12C20O2) PN(CHMe2) PPh2 (L-7) yields both cationic and neutral complexes, [CpRu{eta(2)-(L-7)} PPh3] Cl and [CpRu{eta(1)-(L-7)}(2)PPh3] Cl and [CpRu{eta(2)-(L-7)}Cl]. The reactions of optically pure diphosphazane, Ph2PN(*CHMePh) PPhY (Y = Ph (L-8); Y = N2C3HMe2-3,5 (L-9)) with 1 give the neutral and cationic ruthenium complexes, [CpRu{eta(2)-(Ph2PN(R) PPhY)} Cl] and [CpRu{eta(2)-(Ph2PN(R)PPhY)} PPh3] Cl. "Chiral-at-metal" ruthenium complexes of diphosphazanes have been synthesized with high diastereoselectivity. The absolute configuration of a novel ruthenium complex, (SCSPRRu)-[(eta(5)-C5H5) Ru*{eta(2)-(Ph2PN(*CHMePh)P*Ph( N2C3HMe2-3,5))} Cl] possessing three chiral centers, is established by X-ray crystallography. The reactions of [CpRu{eta(2)-(L-8)} Cl] with mono or diphosphanes in the presence of NH4PF6 yield the cationic complexes, [CpRu{eta(2)-(L-8)}{eta(1)-(P)}] PF6 {P = P(OMe)(3), PPh3, Ph2P(CH2)(n)PPh2 (n = 1 or 2)}.

Reaction of La2CuO4 with binary metal oxides in the solid state: Metathesis, addition, and redox metathesis pathways

Investigation of the reaction of La2CuO4 with several binary metal oxides in the solid state at elevated temperatures has revealed three different reaction pathways. Reaction of La2CuO4 with strongly acidic oxides such as Re2O7, MoO3, and V2O5 follows a metathesis route, yielding a mixture of products: La3ReO8/La2MoO6/LaVO4 and CuO. Oxides such as TiO2, MnO2, and RuO2 which are not so acidic yield addition products: La2CuMO6 (M = Ti, Mn, Ru). SnO2 is a special case which appears to follow a metathesis route, giving La2Sn2O7 pyrochlore and CuO, which on prolonged reaction transform to the layered perovskite La2CuSnO6. The reaction of La2CuO4 with lower valence oxides VO2 and MoO2, on the other hand, follows a novel redox metathesis route, yielding a mixture of LaVO4/LaCuO2 and La2MoO6/Cu, respectively. This result indicates that it is the redox reactivity involving V-IV + Cu-II --> V-V + Cu-I and Mo-IV + Cu-II --> Mo-VI + Cu-0, and not the acidity of the binary oxide, that controls the nature of the products formed in these cases. The general significance of these results toward the synthesis of complex metal oxides containing several metal atoms is discussed.

Structure, function, and mechanism of HhaI DNA methyltransferases

A vast amount of literature has accumulated on the characterization of DNA methyltransferases. The HhaI DNA methyltransferase, a C5-cytosine methyltransferase, has been the subject of investigation for the last 2 decades. Biochemical and kinetic characterization have led to an understanding of the catalytic and kinetic mechanism of the methyltransfer reaction. The HhaI methyltransferase has also been subjected to extensive structural analysis, with the availability of 12 structures with or without a cofactor and a variety of DNA substrates. The mechanism of base flipping, first described for the HhaI methyltransferase, is conserved among all DNA methyltransferases and is also found to occur in numerous DNA repair enzymes. Studies with other methyltransferase reveal a significant structural and functional similarity among different types of methyltransferases. This review aims to summarize the available information on the HhaI DNA methyltransferase.