Reductive Coupling Products Research Articles

First catalytic reductive coupling of 1,3-diynes to carbonyl partners: a new regio- and enantioselective C-C bond forming hydrogenation.

Upon exposure of diynes and glyoxals to cationic Rh(I) catalysts under 1 atm of hydrogen gas, regioselective condensation occurs to afford highly unsaturated enyne products without over-reduction. In the presence of chiral phosphine ligands, reductive coupling products are obtained in high enantiomeric excess at ambient temperature and pressure. The present studies are among the first examples of the electrophilic trapping of organometallic intermediates obtained transiently under the conditions of catalytic hydrogenation.

Regio‐ and Stereoselective Reductive Coupling of Bicyclic Alkenes with Propiolates Catalyzed by Nickel Complexes: A Novel Route to Functionalized 1,2‐Dihydroarenes and γ‐Lactones

Abstract7‐Oxabenzonorbornadienes derivatives 1 a–d underwent reductive coupling with alkyl propiolates CH3CCCO2CH3 (2 a), PhCCCO2Et (2 b), CH3(CH2)3CCCO2CH3 (2 c), CH3(CH2)4CCCO2CH3 (2 d), TMSCCCO2Et (2 e), (CH3)3CCCO2CH3 (2 f) and HCCCO2Et (2 g) in the presence of [NiBr2(dppe)] (dppe=Ph2PCH2CH2PPh2), H2O and zinc powder in acetonitrile at room temperature to afford the corresponding 2alkenyl‐1,2‐dihydronapthalen‐1‐ol derivatives 3 a–n with remarkable regio‐ and diastereoselectivity in good to excellent yields. Similarly, the reaction of 7azabenzonorbornadienes derivative 1 e with propiolates 2 a, b and d proceeded smoothly to afford reductive coupling products 2alkenyl‐1,2‐dihydronapthalene carbamates 3 o–p in good yields with high regio‐ and stereoselectivity. This nickel‐catalyzed reductive coupling can be further extended to the reaction of 7oxabenzonorbornene derivatives. Thus, 5,6‐di(methoxymethyl)‐7‐oxabicyclo[2.2.1]hept‐2‐ene (4) reacted with 2 a and 2 d to furnish cyclohexenol derivatives bearing four cis substituents 5 a and b in 81 and 84 % yield, respectively. In contrast to the results of 4 with 2, the reaction of dimethyl 7oxabicyclo[2.2.1]hept‐5‐ene‐2,3‐dicarboxylate (6) with propiolates 2 a–d afforded the corresponding reductive coupling/cyclization products, bicyclo[3.2.1]γ‐lactones 7 a–d in good yields. The reaction provides a convenient one‐pot synthesis of γ‐lactones with remarkably high regio‐ and stereoselectivity.

Dark- and Photoreactions of Ethanol and Acetaldehyde over TiO2/Carbon Molecular Sieve Fibers

TiO2 has been synthesized within the pores of carbon molecular sieve fibers (CMSF) in order to grow particles of quantum size. TiO2/CMSF characteristics were followed by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and UV–vis diffuse reflectance. XPS showed that all Ti cations are in a +4 oxidation state. The reduction profile of Ti cations (made by preferential O anion removal due to Ar+ sputtering), as evidenced by Ti+x/Ti+4 cations, is very similar to that already observed for well-defined TiO2 surfaces. The absence of XRD pattern indicated that TiO2 particles are in an amorphous form. UV–vis diffuse reflectance showed a considerable blue shift (ΔE=0.6–0.7 eV) of the band gap of TiO2/CMSF when compared to TiO2 (anatase). This shift translates an average particle radius of 15±2 Å. Larger TiO2 particles, outside the CMSF nanopores, are, however, observed by TEM. Dark- and photoreactions of ethanol and acetaldehyde have been investigated over TiO2/CMSF by steady state kinetics and temperature programmed desorption in UHV conditions, as well as in batch conditions at atmospheric pressure. UHV-steady state ethanol reactions have shown eightfold increase in the reaction rate at 573 K in the presence of UV when compared to dark reactions at the same temperatures. The rate constants ratio k2K2/k1K1, for the photoreactions of ethanol, is ca. 40 times higher for TiO2/CMSF than for TiO2 (powder) indicating the high selectivity of the former toward total conversion of ethanol to CO2 with minor accumulation of acetaldehyde (k1K1 and k2K2 are the rate constants for ethanol to acetaldehyde and acetaldehyde to CO2, respectively). Evidence of C–C bond dissociation is given by formaldehyde desorption during UV-acetaldehyde-TPD over TiO2/CMSF under UHV conditions. Moreover, UV-acetaldehyde-TPD indicated a twofold increase of the reductive coupling product (butadiene). The latter requiring Ti+x (x<4) to be formed translates an increase of Ti+x populations under UV illumination.

One-Electron Activation of CO by a Rhodium(II) Porphyrin Bimetalloradical Complex and Concerted Reactions of Two (RhCO)• Units

A rhodium(II) porphyrin bimetalloradical complex, •Rh(CH2)6Rh• (1) reacts with CO and ethene to form an ethanedionyl reductive coupling product, Rh(CH2)6Rh(μ-C(O)C(O)) (2), and an ethylene-bridged complex, Rh(CH2)6Rh(μ-CH2CH2) (4), respectively. Reaction of 1 with 1,3-butadiene proceeds by a 1,4-addition to yield a four-carbon-bridged complex, Rh(CH2)6Rh(μ-CH2CHCHCH2) (5). 1H NMR spectra of 2 and 4 manifest the inherent chirality of two-carbon-bridged tethered diporphyrin complexes. Solutions of 1 and CO react with H2O, CH3CH2OH, and H2 to produce multifunctionalized formyl complexes HRh(CH2)6RhCHO (6), H(O)CRh(CH2)6RhC(O)OCH2CH3 (7), and H(O)CRh(CH2)6RhCHO (8), respectively, but fail to react to an observable extent with methane. Reactivity studies indicate that solutions of 1 and CO function as a source of a species that contains two carbonyl groups (•[OCRh(CH2)6RhCO]•) (3) that are activated toward one-electron reactions at the carbonyl carbon. Reactions of 3 with substrates (H2O, C2H5OH, H2) are discu...

Reactivity of Lanthanide(II) Acetylides Generated from Lanthanide-Benzophenone Complexes and 1-Alkynes.

Ytterbium and samarium-benzophenone complexes react with 1-alkynes to generate lanthanide. (II)acetylides having diphenylmethoxo ligand. It has been found that these acetylides act as reductants as well as nucleophiles, depending on the electrophiles used. Thus, their reaction with aldehydes and aliphatic ketones gives propargylic alcohols in good yields, while, with aromatic ketones and alkyl halide, the reductive coupling products are obtained selectively.

Stereoselective Formation oftrans-Decalin andcis-Decalin Skeletons via Hydroxy Group Directed Cyclization Induced by Samarium(II) Iodide

By treating the anti-hydroxyketones (1 and 2) and the syn-hydroxyketones (4 and 5) with samarium(II) iodide, the ketone-olefin coupling cyclizations took place in a stereocontrolled manner to give the trans-decalin diol (3) and the epimeric mixtures of the cis-decalin diols (6 and 7) respectively. The observed stereochemistries on the reductive coupling products are established by chelation of the samarium(III) cation generated in the process, with the hydroxyl groups incorporated in the starting materials.

Organocerium reagents from iodine activated cerium metal and organic iodides: Their reactions with carbonyl compounds

Cerium metal activated by a trace of iodine reacted smoothly with alkyl, allyl, and aryl iodides to give the corresponding organocerium reagents. The reaction of the organocerium reagents thus prepared in situ with carbonyl compounds gave not only Grignard-type adducts but also reduction and reductive coupling products.

Intramolecular rearrangements of sulfines coordinated to platinum. A unique equilibrium between oxidative-addition stereoisomers cis-(E)- and cis-(Z)-bis(triphenylphosphine)(methylthio)(arylsulfine)platinum(II) and the two stereoisomers of the reductive coupling product bis(triphenylphosphine)[aryl(methylthio)sulfine]platinum(0). Crystal and molecular structure of bis(triphenylphosphine)(9-sulfinylfluorene)platinum(0)-0.5-benzene

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIntramolecular rearrangements of sulfines coordinated to platinum. A unique equilibrium between oxidative-addition stereoisomers cis-(E)- and cis-(Z)-bis(triphenylphosphine)(methylthio)(arylsulfine)platinum(II) and the two stereoisomers of the reductive coupling product bis(triphenylphosphine)[aryl(methylthio)sulfine]platinum(0). Crystal and molecular structure of bis(triphenylphosphine)(9-sulfinylfluorene)platinum(0)-0.5-benzeneJohan W. Gosselink and Gerard Van KotenCite this: Inorg. Chem. 1981, 20, 3, 877–884Publication Date (Print):March 1, 1981Publication History Published online1 May 2002Published inissue 1 March 1981https://doi.org/10.1021/ic50217a047RIGHTS & PERMISSIONSArticle Views37Altmetric-Citations16LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (952 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Reactions of organic halides and cyanides with bis(tricyclohexylphosphine)nickel(0)

The reactions of the complex bis(tricyclohexylphosphine)nickel(0) (Ni(PCy 3) 2) with organic halides and cyanides RX (R  CH 3, X  I, CN; R  C 2H 5, X  Br, I, CN; R  C 3H 7, X  Br, CN; R  C 6H 5, X  Cl, CN), all involving fission of the RX bond, have been studied in toluene at various temperatures. Oxidative addition of the bromides produces the stable complexes [Ni IBr(PCy 3) 2] 2 and Ni II (H)(Br)(PCy 3) 2. Methyl iodide affords phosphonium salts of a nickel(II) complex. The organic products of these reactions involve alkanes, alkenes, benzene, and reductive coupling products RR. Except for the methyl and phenyl derivatives the distribution of organic products is rather insensitive to the functional group X. The reactions are discussed in terms of molecular and radical mechanisms. The reactivity of Ni(PCy 3) 2 is compared with that of Ni(PEt 3) 3 and Ni(PMe 3) 4.

ChemInform Abstract: PHOTOREACTIONS OF FLAVANONES

AbstractFlavanon (Ia) und seine Derivate (Ib)‐(Id) gehen beim Bestrahlen in Benzol oder ,anderen inerten Lösungsmitteln in die entsprechenden 2‐Hydroxychalkone (IIa)‐(IId) über, deren Ausb. unter anderem vom verwendeten Lösungsmittel abhängen.

Photoreactions of Flavanones

Abstract Parent and substituted flavanones undergo photochemical opening of the pyrone ring to give corresponding 2′-hydroxychalcones in benzene, pyridine, acetonitrile etc., the yields varying from 0 to 70% with substituents. The reaction is depressed by the addition of 1,3-pentadiene, nitrosobenzene, or acrylonitrile. On the other hand, flavanone and 4-chromanone undergo photoreduction in 2-propanol to give reductive coupling products and solvent adducts as isomeric mixtures. 7,8-Benzoflavanone does not undergo photoreduction in 2-propanol but the ring opening reaction instead. Mechanisms have been discussed in terms of the relative contribution and π,π* character in the lowest triplet states.

Reductive coupling of aromatic compounds

Benzene mixed with hydrogen fluoride and a platinum or rhodium catalyst is hydrogenated at room temperature and 1–5 atm pressure to yield cyclohexane and a reductive coupling product, phenylcyclohexane, the latter amounting to as much as 25% by weight of the hydrogenation products. Similarly, reductive coupling products are obtained from phenol or chlorobenzene, the former giving cyclohexylidine diphenol and the latter a mixture of monochlorinated phenylcyclohexanes. Results are consistent with the assumption that these reactions proceed by way of cycloalkene intermediates which react with unchanged aromatic compound to form the reductively coupled products. Readily available equipment for such hydrogenations is described.

Mechanism of Chloroplatinic acid Catalyzed Reduction of Alkyl Halides by Hydrosilanes

The chloroplatinic acid catalyzed reduction of alkylhalides by organosilicon hydrides has been assumed to proceed through a quasi-free-radical mechanism. This paper presents evidence to support such assumption. Namely, (1) selectivity found in this reduction is comparable with that effected in peroxide catalyzed reductions ; (2) some benzylic halides give the corresponding reductive coupling products (3) the characteristic color of diphenylpicrylhydrazyl in triethylsilane fades rapidly in the presence of chloroplatinic acid; and (4) the Hammett correlation for the relative rates of substituted chloroform (X-CC13) toward triethylsilane in the presence of chloroplatinic acid gives a ρ* value of +0.28, which essentially agrees with the value of +0. 29 previously found for the reaction of triethylsilyl radicals.