3073-51-6Relevant articles and documents
Effects of Structure on Rates and Quantum Yields in Photoreduction of Fluorenone by Amines. Catalysis and Inhibition by Thiols
Stone, Paul G.,Cohen, Saul G.
, p. 3435 - 3440 (1982)
Rate constants, kir, quantum yields, φred, and effects of thiol have been studied in the photoreduction of fluorenone by amines in benzene.Hydroxyethylamines show increased φred as compared with unsubstituted ethyl analogues, φred ca.0.8 with triethylamine, but ca.2, the maximum theoretical value, with triethanolamine and 2-(diethylamino)ethanol.Abstraction is predominantly from unsubstituted ethyl groups in the latter, and increased kir and φred are attributed to solvation by hydroxyl, present only at the reaction site, of polar intermediates or transition states.Secondary amines have high kir and low φred, 0.01-0.2, attributed to predominant abstraction of H from N and disproportionation of ketyl and aminyl radicals.This reduction is strongly catalyzed by aliphatic thiol, as aminyl radical abstracts H from S and thiyl radical abstracts H from α-C of amine.Primary amines have low kir and φred.This reduction is not catalyzed by thiol, indicating that H is not abstracted by triplet fluorenone from N of primary aliphatic amines.Aniline inhibits this reduction, but aniline plus thiol leads to strong catalysis.Triplet fluorenone abstracts H from N of aniline, anilino radical abstracts H from S of thiol, and thiol abstracts H from α-C of amine, leading to effective reduction.Thiol catalysis may be diagnostic for the formation of aminyl radicals.Inhibition and catalysis by thiols are discussed.
Vanadium(I) chloride and lithium vanadium(I) dihydride as selective epimetallating reagents for π- and σ-bonded organic substrates
Eisch, John J.,Fregene, Paul O.
scheme or table, p. 4482 - 4492 (2009/05/07)
Subvalent vanadium(I) salts, of empirical formulas, VCl, vanadium(I) chloride and LiVH2, lithium vanadium(I) dihydride, whose efficient preparation, structural constitution and mode of reaction toward certain organic substrates have been described in a preceding article, are here evaluated in their reactions toward a wide variety of π- and σ-bonded organic substrates, namely carbonyl, imine, azo, alkene, 1,3-diene, nitrile π-bonds and C-X, C-O, C-N and N-N σ-bonds. Compared with the high reactivity of CrCl and LiCrH2 reagents in attacking both types of bonds, the VCl and LiVH2 reagents were much milder and selective in epimetallating π-bonds, often forming the 1:1 adduct of LiVH2 and π-bonded substrate as the major product. Finally, the vanadium reagents showed little tendency to cleave C-O, C-S and C-N bonds and a smaller scope in cleaving C-X bonds than their chromium counterparts. Because of their selectivity these vanadium reagents offer the following preparative promise: 1) smooth McMurry carbonyl coupling to their reductive dimers; 2) deoxygenation of epoxides; 3) selective aromatic C-X reduction; 4) high yields of epimetallated carbonyls or imines as intermediates to α-hydroxy and α-amino acids; 5) 1,4-reductions of 1,3-alkadienes; 6) reductive dimerization of nitriles to ketones; 7) 1,4 or 1,n-epimetallations leading to acyloins or indoles; and 8) reductive dimerizations of azines to produce unusual imidazole derivatives. In explaining the greater kinetic stability of the 1:1 LiVH2 adduct with carbonyl or imine substrates it is pointed out that such epimetallated adducts from LiVH2 would likely be diamagnetic, whereas such adducts from LiCrH2 have an unpaired electron on the Cr center and hence would rupture, so that the electron would be on the C center. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
Vanadium(I) chloride and lithium vanadium(I) dihydride as epimetallating reagents for unsaturated organic substrates: Constitution and mode of reaction
Eisch, John J.,Fregene, Paul O.,Doetschman, David C.
experimental part, p. 2825 - 2835 (2009/04/07)
Subvalent vanadium(I) salts, of empirical formulas, VCl, vanadium(I) chloride and LiVH2, lithium vanadium(I) dihydride, can be conveniently prepared in THF solution, starting at -78 °C, by treating either VCl3 or VCl4 with an appropriate number of equivalents of nBuLi. As judged by the stability of solutions or solid samples of LiVH2, the preparation of LiVH2 from VCl4 is the preferred method. Individual physical characterization of solid samples of VCl or of LiVH2, admixed with their LiCl by-product, was carried out after removal of all volatiles in vacuo and by the following measurements: 1) gasometric protolysis with glacial acetic acid and measurement of the H 2 evolved in the oxidation of VI to VII; 2) infrared spectroscopic search for V-H bands; and 3) examination for unpaired electrons by EPR activity. Such measurements applied to VCl lend strong support for a VI oxidation state but only probable evidence for paramagnetism and for the association of VCl units. Similar measurements applied to LiVH 2 give unambiguous gasometric and IR evidence favoring the LiVH 2 stoichiometry and the biradical nature of the VH2 anion with a linear array of H-V-H atoms. Chemical characterization of both VCl and LiVH2 toward individual organic substrates, such as olefins, ketones, epoxides and organic halides, yielded convincing evidence that organic radical mechanisms are involved, both for the proven biradical, LiVH2, as well as for the diamagnetic VCl. Finally, the question of why LiVH2 prepared from VCl4 is more stable than the LiVH2 obtained from VCl3 is addressed in terms of the actual coordination sphere of the VH2 anion in THF solution and in the solid state. Preliminary studies comparing the reactivities of LiVH2 and LiCrH2 toward organic substrates indicate that LiVH2 is the distinctly more moderate and usefully selective reductant. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
Samarium/N-bromosuccinimide-induced reductive dimerization of carbonyl compounds
Banik, Bimal K.,Banik, Indrani,Samajdar, Susanta,Cuellar, Rogelio
, p. 2319 - 2322 (2007/10/03)
Stereoselective reductive coupling of carbonyl compounds has been achieved using samarium/N-bromosuccinimide in methanol. The combination of these agents has proved a powerful addition to the arsenal of samarium-based reductants currently utilized.
Facile reduction of aromatic aldehydes, ketones, diketones and oxo aldehydes to alcohols by an aqueous TiCl3/NH3 system: Selectivity and scope
Clerici, Angelo,Pastori, Nadia,Porta, Ombretta
, p. 3326 - 3335 (2007/10/03)
A simple and rapid procedure for the almost quantitative reduction of aromatic aldehydes, ketones, diketones and oxo aldehydes to alcohols by use of TiCl3/NH3 in aqueous methanol solution is reported. The reducing system distinguishes between different classes of aldehydes and/or ketones, and many functionalities that usually do not survive under reducing conditions are tolerated well. The concept of reversal of chemoselectivity has also been developed. A mechanism based on two sequential one-electron transfers from TiIII to the carbonyl carbon atom is proposed, the second SET becoming operative only in the presence of ammonium ion (either added or formed in situ). Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
Samarium-induced alkyl halide mediated reductive coupling of ketones
Ghatak, Anjan,Becker, Frederick F.,Banik, Bimal K.
, p. 3793 - 3796 (2007/10/03)
Reductive coupling of aromatic ketones was achieved by samarium metal in the presence of alkyl halides. (C) 2000 Published by Elsevier Science Ltd.
Organometallic chemistry sans organometallic reagents: Modulated electron-transfer reactions of sub valent early transition metal salts
Eisch, John J.,Shi, Xian,Alila, Joseph R.,Thiele, Sven
, p. 1175 - 1187 (2007/10/03)
The potential of low-valent, early transition-metal reagents as selective reductants in organic chemistry has been foreshadowed by intensive research on the ill-defined and heterogeneous subvalent titanium intermediates generated in the McMurry reaction and its numerous variants. As part of a long-term research effort to develop soluble, well-defined transition-metal reductants of modulated and selective activity toward organic substrates, the THF-soluble reductant, titanium dichloride, has been thoroughly examined, as well as the analogous ZrCl2 and HfCl2 reagents, all of which are readily obtainable by the alkylative reduction of the Group 4 tetrachloride by butyllithium in THF. Noteworthy is that such interactions of MCl4, with butyllithium in hydrocarbon media lead, in contrast, to M(III) or M(IV) halide hydrides. Analogous alkylative reductions in THF applied to VCl4, CrCl3, and MoCl5 have yielded reducing agents similar to those obtained from MCl4 but gradated in their reactivity. Such reductants have proved capable of coupling carbonyl derivatives, benzylic halides, acetylenes and certain olefins in a manner consistent with an oxidative addition involving a two-electron transfer (TET). Such a reaction pathway is consistent with the observed stereochemistry for pinacol formation from ketones and for the reductive dimerization of alkynes. In contrast to the reaction of CrCl3 with two equivalents of butyllithium, which leads to a CrCl intermediate, the interaction of CrCl3 in THF with four equivalents of butyllithium at -78°C yields a reagent of the empirical formulation, LiCrH4 · 2 LiCl · 2 THF, as supported by elemental and gasometric analysis of its protolysis. This hydridic reductant cleaves a wide gamut of o carbon-heteroatom bonds (C-X, C-O, C-S and C-N), towards which the CrCl reductant is unreactive. The type of cleavage and/or coupled products resulting from the action of "LiCrH4" on these substrates is best understood as arising from single-electron transfer (SET). In light of the aforementioned findings, the gradated reducing action noted among TiCl2, ZrCl2, HfCl2 and CrCl, as well as the contrasting reducing behavior between CrCl and LiCrH4, there is no doubt that future research with early transition metals will continue to yield novel reductants of modulated and site-selective reactivity. VCH Verlagsgesellschaft mbH,.
Nickel(0)-induced geminal bond cleavages leading to carbon-carbon double bonds: Intermediacy of nickel(0)-carbene complexes as a unifying hypothesis
Eisch, John J.,Qian, Yun,Singh, Mona
, p. 207 - 217 (2007/10/03)
The possibility of effecting geminal bond cleavages of organic monomers with nickel(0) complexes to achieve olefinic dimers has been investigated both in stoichiometric reactions between monomers of the type R2CE2 and R2C=E and the complexes (Cod)2Ni, (Et3P)4Ni and (Bpy)(Cod)Ni and in nickel(0)-catalytic α-elimination reactions of α-lithioorganic sulfones, RR′C(Li)(SO2R″). Substrates for the stoichiometric geminal bond cleavages comprised geminal dihalides, aminomethyl sulfides, cyclopropenes, thioketones and ketones. Reductive dimerization to the olefin or its hydroxy derivatives was found to occur to a varying degree in most cases, including the catalytic decomposition of the α-lithioorganic sulfones. Accordingly, this method offers considerable promise in organic synthesis. A gamut of known nickel(0) chemistry, results of chemical-trapping and spectroscopic evidence are marshaled in support of the proposal that such geminal bond cleavages and reductive coupling processes most likely proceed via nickel(0)-carbene intermediates of the type R2C=Ni · Ln.
Arene Hydrides, Reaction of Anthracene Hydride (Anion of 9,10-Dihydroanthracene) with Diaryl Ketones. Base-Induced Fragmentation of the Carbonyl Adduct
Sommer, Andreas,Stamm, Helmut,Woderer, Anton
, p. 387 - 390 (2007/10/02)
With benzophenone (1a) and fluorenone (1b) anthracene hydride (AH-) rapidly forms the anions 3a, b of the corresponding tertiary alcohols 4a, b, the intense colour of the reaction mixture indicating the presence of the ketyls 2a, b.Excess of AH- converts 3a, b into the diarylcarbinols.A mechanism is proposed for this ketone reduction.
Transferts d'electrons assistes par les metaux de transition: influence de la nature du cation metallique sur la reduction de composes carbonyles en milieu aprotique
Fournier, Francoise,Fournier, Michel
, p. 881 - 890 (2007/10/02)
The pinacolisation of ketones is enhanced when a bivalent transition metal cation is present.This phenomenon is general and occurs with Cr2+, Mn2+, Fe2+, Co2+, Zn2+ but not with Ni2+.The cathodic reduction leads to α-glycols with a good yield, without any resin production, and at a less negative potential than that of the ketone itself.The distribution of all isolated compounds is dependent on the Lewis character-acidity and complexing power of the metallic cation.Thus, for the dimerization, the greatest specificity is generally observed when Fe2+ is present.For the chalcone, the better stereoselectivity is obtained with Zn2+.No evidence of initial carbonyl complex of the metal ion was shown.
