‘Reductive Heck reaction’ of 6-halopurines

Alkenylation of 9-benzyl-6-halopurines with alkenes does not proceed under conventional Heck conditions. However, in the presence of triethylammonium formate a mixture of the corresponding saturated products was obtained. In contrast to the classical Heck reaction, the regioselectivity of this process is low giving a mixture of both α- and β-products regardless of the electronic nature of the substituent on the double bond of the alkene.     

Reductive dissolution of microparticulate manganese oxides

Electrochemical dissolution of immobilised microparticulate Mn(III,IV) oxides in slightly acidic solution (pH 4.4) was found to be a very general reaction, which is responsible for well-defined voltammetric peaks. Dissolution of six Mn(III,IV) oxides is initiated by the reduction of Mn(IV) to Mn(III) in the solid phase, which is followed by a massive dissolution via further reduction of Mn(III) to Mn(II), which finally yields soluble Mn²⁺. The reactivity of manganese oxides depends on their structure: the most reactive are amorphous (δ-MnO₂) and layered structures (birnessite); more resistant toward reductive dissolution are α- and λ-MnO₂ and electrochemical manganese dioxide; and least reactive is β-MnO₂. Reductive dissolution of LiMn₂O₄ resembles that of λ-MnO₂, whereas CaMnO₃ dissolves via a different reaction mechanism.     

Synthesis of new tripodal receptors—a ‘PET’ based ‘off-on’ recognition of Ag

A new set of tripodal receptors based upon an aromatic platform have been synthesized in high yields. The compounds have been characterized by spectroscopic techniques and by single crystal X-ray crystallography. These receptors are found to have good extraction ability and high transport rate for Ag(I). The receptor with imine linkages exhibits weak fluorescence emission bands at λ_max=413 and 540 nm, upon excitation at λ_max=365 nm. The fluorescence spectrum of the receptor shows enhancement in the intensity of the signal at 413 nm on binding with the Ag⁺ cation. No such significant changes are observed with other metal ions. An absorption at ∼365 nm is typical of an intraligand (π-π^∗) transition involving the imine chromophore, which produces a weak emission band at 413 nm due to quenching caused by PET from a neighboring -OH group. Participation of OH group in coordination to the metal ion reduces PET and an enhancement of fluorescence intensity is observed, signaling recognition of the metal ion.     

2′-Lipid-modified oligonucleotides via a ‘Staudinger-Vilarrasa’ reaction

We report a new access to 2′-amido-2′-deoxyuridine via a Staudinger-Vilarrasa coupling reaction for the preparation of lipid-modified oligonucleotides. One or two lipidic moieties were inserted within the oligonucleotidic sequence (LONs) leading to a repertoire of original antagomir-like molecules targeting micro RNA (miRNA or miR). Melting temperature (Tm) experiments revealed that the stability of the duplexes depends on the lipid position and the number of lipid moieties inserted within the oligonucleotide sequence. Single lipid conjugations of positions 11 and 19 of LONs targeting miR-122 do not destabilize the duplexes.     

‘Sugaring’ carbosilane dendrimers via hydrosilylation

Two new pathways to introduce carbohydrate derivatives into dendritic carbosilane structures were explored. Pathway one utilised alcoholysis of a chlorosilane with a protected hydroxyethyl glycoside resulting in Si-O linkages. Pathway two proceeds via a hydrosilylation reaction of a protected allyl glycoside with a carbosilane containing Si-H end groups in the presence of a platinum catalyst, thus leading to Si-C linked structures.     

羰基氧化物RR^1COO的电子结构

本文采用6-31G基组的abinitio方法对羰基氧化物RR^1COO(R,R^1=H,F,CH~3)进行几何构型优化计算,研究其基态的电子结构。结果表明,RR^1COO的稳定结构为双自由基型,其单重态和双重态的相对稳定性受取代基的影响。H~2COO、H(CH~3)COO和(CH~3)~2COO的基态为单重态(^1A),HFCOO和F~2COO的基态为三重态(^3A),HFCOO和H(CH~3)COO的顺式结构比反式稳定。     

Reductive coupling of carbonyl compounds using lanthanum metal

We found that lanthanum metal was an excellent agent for the reduction of carbonyl compounds in the presence of a catalytic amount of iodine. When carbonyl compounds were treated with lanthanum metal in the presence of a catalytic amount of iodine, the reductive coupling of the carbonyl compounds proceeded efficiently to afford the corresponding vic‐diols in moderate to good yields. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:81–85, 2000     

Synthesis and fragmentation of new 2‐phosphabicyclo[2.2.2]octene 2‐oxides

The substitution pattern of the 2‐phosphabicyclo[2.2.2]octene framework and the skeleton itself were varied to obtain new cycloadducts usable in phosphorylations and to study their ability to undergo fragmentation. Thus, an N‐methyl and several P‐trialkylphenyl derivatives ( 7 and 9 , respectively) were synthesized, together with two diaza species ( 8 ) whose stereostructure was evaluated by single crystal X‐ray analysis. Mechanistic studies on the UV light‐mediated photolysis of the P‐aryl phosphabicyclooctenes ( 9 ) in the presence of methanol supports the suggestion of a novel addition–elimination reaction path. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:626–632, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10052     

Si—H Functional Polysilanes via a Homogeneous Reductive Coupling Reaction

A polysilane copolymer with reactive Si—H side groups was obtained through a homogeneous coupling reaction of dichlorodiphenylsilane with dichloromethylsilane. The reaction was carried out in a tetrahydrofuran (THF) solution of a sodium‐potassium alloy complex with 18‐crown‐6 with a well defined composition of alkali metal ion pairs (Mt⁺/crown ether, Mt^–) at –75°C. The product was characterized using ¹H NMR, ¹³C NMR, FT‐IR and UV/Visible spectroscopies and gel permeation chromatography. The results were compared with those obtained by the heterogeneous coupling reaction of the same monomers.     

UFU (‘Ullmann-Finkelstein-Ullmann’): a new multicomponent reaction

We developed conditions to carry out the first ‘one-pot’ Ullmann-Finkelstein-Ullmann multicomponent reaction reported. This reaction allows the one-pot synthesis of dissymmetrical para-disubstituted benzene scaffold from 1-bromo-4-iodobenzene and two N-nucleophiles. CuI/N,N′-dimethyl-cyclohexane-1,2-diamine was used as a catalyst/ligand couple, K₃PO₄ as a base and the reaction was performed in dioxane.     

Synthesis of ‘inside-outside’ medium-sized rings via ring-closing metathesis

Functionalized and unfunctionalized dienes were synthesized from lactones 7 and 6, respectively, which were subjected to ring-closing metathesis (RCM) using Grubbs’ catalysts. These dienes provide a systematic study of the stereochemical requirements for efficient cyclization. Moreover, it has been established that, within a uniquely defined oxabicyclo[3.3.0]octane template, medium sized rings bearing an ‘in-out’ intrabridgehead stereochemical relationship can been synthesized in good yield.     

LiAlH4/silica chloride as a new chemoselective system for reduction of carbonyl compounds and phosphine oxides

LiAlH₄/silica chloride system was used as an efficient and chemoselective reductant for organic substrates. The reduction of phosphine oxides was achieved with this system. Good chemoselectivity in reduction of aldehydes and ketones in the presence of other carbonyl compounds was observed.     

Organic bonding to silicon via a carbonyl group: new insights from atomic-scale images

The ability to covalently attach organic molecules to semiconductor surfaces in a controllable and selective manner is currently receiving much attention due to the potential for creating hybrid silicon-organic molecular-electronic devices. Here we use scanning tunneling microscopy (STM) and density functional theory calculations to study the adsorption of a simple ketone [acetone; (CH(3))(2)CO] to the silicon (001) surface. We show both bias and time-dependent STM images and their agreement with total energy DFT calculations, simulated STM images, and published spectroscopic data. We investigate the stability of the resulting adsorbate structures with respect to temperature and applied STM tip bias and current. We demonstrate the ability to convert from the kinetically favored single-dimer alpha-H cleavage adsorbate structure to thermodynamically favored bridge-bonded adsorbate structures. This can be performed for the entire surface using a thermal anneal or, for individual molecules, using the highly confined electron beam of the STM tip. We propose the use of the carbonyl functional group to tether organic molecules to silicon may lead to increased stability of the adsorbates with respect to current-voltage characterization. This has important implications for the creation of robust single-molecule devices.     

Reductive coupling of carbon monoxide in a rhenium carbonyl complex with pendant Lewis acids

Phosphinoborane ligands impart unique reactivity to a rhenium carbonyl cation relative to simple phosphine complexes. Addition of either triethylborohydride or a platinum hydride (that can be formed from H2) forms a rhenium boroxycarbene. This carbene, which crystallizes as a dimer, disproportionates over a period of days to afford the starting cation and a structurally unprecedented boroxy(boroxymethyl)carbene, in which a new C-C bond has been formed between two reduced CO ligands. This product of C-C bond formation can be independently synthesized by addition of 2 equiv of hydride to the rhenium carbonyl cation.     

Reductive amination of carbonyl compounds using NaBH4 in a Brønsted acidic ionic liquid

Reductive amination of carbonyl compounds using sodium borohydride is conducted in the Brønsted acidic ionic liquid, 1-methyl imidazolium tetrafluoroborate ([HMIm][BF₄]). The ionic liquid plays the dual role of solvent as well as catalyst for efficient conversion of aldehydes and ketones to amines in excellent yields without the formation of side products.     

Efficient production of raspberry ketone via ‘green’ biocatalytic oxidation

For the development of a ‘green’ oxidation method, the transformation of 4-(p-hydroxyphenyl)butan-2-ol (rhododendrol) into 4-(p-hydroxyphenyl)butan-2-one (raspberry ketone) was used as a model reaction. Different lyophilized cells of Rhodococcus spp. have been screened for their ability to perform the desired oxidation. Rhodococcus equi IFO 3730 and R. ruber DSM 44541 were able to use acetone as a hydrogen acceptor in a hydrogen transfer-like process. The oxidation can be performed at substrate concentrations up to 500 g/L.     

Absolute rate constants of decay of aryl-substituted carbonyl oxides

The decay kinetics of a series of carbonyl oxides (CbO)—4-methylbenzophenone oxide, 2,5-dimethylbenzophenone oxide, 4-chlorobenzophenone oxide, 2-bromobenzophenone oxide, and acetophenone oxide—were studied by the pulse photolysis technique in acetonitrile, benzene,n-decane, andn-pentane. The absorption spectra were studied, and the absorption coefficients and absolute rate constants of CbO decay were determined. The absorption maxima observed in the spectra of carbonyl oxides range within 405±25 nm. The decay rate constant was found to depend on both the CbO structure and the medium. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 677–681, April, 1999.     

Reductive coupling of carbonyl compounds to pinacols by using low-valent cerium

Aldehydes and ketones, on treatment with a low-valent cerium reagent, undergo reductive dimerization to produce the corresponding pinacols in high yield.     

Effects of the substituents on the reactivity of carbonyl oxides. A theoretical study on the reaction of substituted carbonyl oxides with water

The reactions between fifteen carbonyl oxides and water have been investigated with the aim of contributing to a better understanding of the effects of the substituents in the reactivity of carbonyl oxides. We have employed density functional theory and large scale ab initio methods (CCSD(T), CASSCF, and CASPT2), combined with transition state theory, to investigate the addition of water to carbonyl oxide and, for those carbonyl oxides having a methyl substituent in syn, the hydrogen transfer from the methyl group to the terminal oxygen of carbonyl oxide. In this case, the water acts as a catalyst and this reaction can contribute to the atmospheric formation of a hydroxyl radical. Carbonyl oxides with electron withdrawing substituents and zwitterionic character have low energy barriers and react fast, whereas carbonyl oxides with electron releasing substituents have high energy barriers and react slowly. The position of the substituents plays also an important role and carbonyl oxides having a hydrogen atom substituent in syn react faster than carbonyl oxides having a hydrogen atom substituent in anti. The differences in the reactivity of different substituted carbonyl oxides raise up to ten orders of magnitude and the branching ratios for the two different reactions investigated are also reported.