1007-03-0Relevant articles and documents
An efficient and transition metal free protocol for the transfer hydrogenation of ketones as a continuous flow process
Sedelmeier, Joerg,Ley, Steven V.,Baxendale, Ian R.
, p. 683 - 685 (2009)
We report the efficient reduction of a selection of ketones to the corresponding secondary alcohols using only catalytic amounts of LiOtBu in iPrOH facilitated by using a continuous flow reactor.
Mandell et al.
, p. 1616 (1978)
On the Mechanism of the Reduction of Some Ketones by Organotin Hydrides.Hydride Transfer, Electro-Transfer-Hydrogen-Atom Abstraction, or Free Radical Addition.
Tanner, Dennis D.,Diaz, Gilberto E.,Potter, Alan
, p. 2149 - 2154 (1985)
Three aromatic-aliphatic ketones, cyclopropyl phenyl ketone, α,α,α-trifluoroacetophenone and α-fluoroacetophenone, are reduced by triphenyltin hydride by an initiated homolytic reaction to yield organic stannoxides.The reactivity is is not markedly dependent upon solvent polarity.The unitiated reduction with triphenyltin hydride of the more reactive electronegatively substituted fluorinated alkyl-aromatic ketones show a solvent-dependent reactivity.The reactivity increases as the solvent becomes more polar.Both homolytic and heterolytic processes occur in the more polar solvents.The homol ytic reaction appears to be initiated by an electron-transfer process, and the propagation sequence, likewise, contains an electron-transfer step.It appears that in the propagation step the donor-acceptor ability of the reagents determine whether the homolityc reaction proceeds by a radical addition of a tin to the carbonyl oxygen or whether electron transfer occurs prior to tin-oxygen bond formation.A consideration of the timing of these processes suggests a merged mechanism where the donor-acceptor ability of the reagents determines the extent of electron transfer in or after the transition state.
Molecularly Defined Manganese Pincer Complexes for Selective Transfer Hydrogenation of Ketones
Perez, Marc,Elangovan, Saravanakumar,Spannenberg, Anke,Junge, Kathrin,Beller, Matthias
, p. 83 - 86 (2017)
For the first time an easily accessible and well-defined manganese N,N,N-pincer complex catalyzes the transfer hydrogenation of a broad range of ketones with good to excellent yields. This cheap earth abundant-metal based catalyst provides access to useful secondary alcohols without the need of hydrogen gas. Preliminary investigations to explore the mechanism of this transformation are also reported.
Evidence for heterolytic cleavage of a cyclic oxonium ylide: Implications for the mechanism of the Stevens [1,2]-shift
Hosseini, Seyedeh Nargess,Johnston, Jeffrey R.,West
, p. 12654 - 12656 (2017)
Formation and rearrangement of several oxonium ylides containing cyclopropylcarbinyl migrating groups were studied. Efficient ring-contraction by [1,2]-shift to form cyclopropane-substituted cyclobutanones was observed, with no competing cyclopropane fragmentation. Substitution with the hypersensitive mechanistic probe (trans,trans-2-methoxy-3-phenylcyclopropyl)methyl led to cyclopropane fragmentation via an apparent heterolytic pathway, providing the first evidence for ion pair intermediates from ylide cleavage, and suggesting a possible alternative heterolytic mechanism for the Stevens [1,2]-shift.
Practical (asymmetric) transfer hydrogenation of ketones catalyzed by manganese with (chiral) diamines ligands
Wang, Ding,Bruneau-Voisine, Antoine,Sortais, Jean-Baptiste
, p. 31 - 36 (2018)
The reduction of ketones with 2-propanol as reductant was achieved using an in-situ generated catalytic system based on manganese pentacarbonyl bromide, as metal precursor, and ethylenediamine as ligand. The reaction proceeds in high yield at 80 °C, in 3 h, with 0.5 mol% of catalyst. In the presence of chiral (1R,2R)-N,N′-dimethyl-1,2-diphenylethane-1,2-diamine, as the ligand, sterically hindered alcohols were produced with enantiomeric excess up to 90%.
Polylithiation of thioethers: A versatile route for polyanionic synthons
Yus, Miguel,Gutiérrez, Ana,Foubelo, Francisco
, p. 4411 - 4422 (2001)
The successive reaction of phenyl vinyl thioether (1) with n-butyllithium and an electophile [E1=PhCHO, (CH2)4CO, (CH2)5CO] in THF at - 78°C gives, after hydrolysis, the expected methylenic hydroxy thioethers (2). Deprotonation of 2 with n-butyllithium followed by a DTBB-catalysed lithiation and reaction with a second electrophile [E2=tBuCHO, PhCHO, Me2CO, (CH2)5CO], at - 78°C, gives after hydrolysis the corresponding methylenic diols 3. The same diols can be prepared starting from 1 in a one-pot process without isolation of the hydroxy thioether 2. The same methodology was applied to the cyclopropyl phenyl thioether (4), cyclopropyl 1,3-diols 5 {E1=tBuCHO, PhCHO, [Me(CH2)4]2CO, (CH2)5CO, (CH2)7CO; E2=tBuCHO, Me2CO, (CH2)5CO} being isolated in moderate yields. The successive treatment of bis(phenylthio)methane (7) with: (a) n-butyllithium at 0°C, (b) a carbonyl compound [E1=tBuCHO, Me2CO, Et2CO, (CH2)5CO] at - 40°C, (c) lithium and catalytic amount of DTBB (5%) and (d) a second carbonyl compound [E2=iPrCHO, tBuCHO, Me2CO, Et2CO, (CH2)5CO] both at - 78°C leads, after hydrolysis, to the expected dihydroxy thioethers 8. When after step (d), a second DTBB-catalysed lithiation is performed at temperatures ranging between - 78 and 20°C, the corresponding allylic alcohols 9 were isolated. Finally, treatment of alcohols 9 with a few drops of 6 M hydrochloric acid gives dienes 10 in almost quantitative yields.
Photoinduced Palladium-Catalyzed Dicarbofunctionalization of Terminal Alkynes
Yang, Zhen,Koenigs, Rene M.
, p. 3694 - 3699 (2021)
Herein, a conceptually distinct approach was developed that allowed for the dicarbofunctionalization of alkynes at room temperature using simple, bench-stable alkyl iodides and a second molecule of alkyne as coupling partner. Specifically, the photochemical activation of palladium complexes enabled this strategic dicarbofunctionalization via addition of alkyl radicals from secondary and tertiary alkyl iodides and formation of an intermediate palladium vinyl complex that could undergo subsequent Sonogashira reaction with a second alkyne molecule. This alkylation–alkynylation sequence allowed the one-step synthesis of 1,3-enynes including heteroarenes and biologically active compounds with high efficiency without exogenous photosensitizers or oxidants and now opens up pathways towards cascade reactions via photochemical palladium catalysis.
A Novel Mechanism for the Conversion of α-Cyclopropylbenzyl Alcohol into γ-Trimethylsilylbutyrophenone
Hwu, Jih Ru
, p. 452 - 453 (1985)
Mechanistic studies of the reaction between α-cyclopropylbenzyl alcohol and methyl-lithium followed by hexamethyldisilane indicate that disproportionation of intermediate (4) with trimethylsilyl anion as catalyst provides cyclopropyl phenyl ketone; in situ 1,4-addition of trimethylsilyl anion to the latter compound leads to the major product, γ-trimethylsilylbutyrophenone (2).
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Shono,T. et al.
, p. 421 - 425 (1968)
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Ligand Effect in Alkali-Metal-Catalyzed Transfer Hydrogenation of Ketones
Alshakova, Iryna D.,Dudding, Travis,Foy, Hayden C.,Nikonov, Georgii I.
, (2019)
This work unveils the reactivity patterns, as well as ligand and additive effect on alkali-metal-base-catalyzed transfer hydrogenation of ketones. Crucially to this reactivity is the presence of a Lewis acid (alkali cation), as opposed to a simple base effect. With aryl ketones, the observed reactivity order is Na+>Li+>K+, whereas for aliphatic substrates it follows the expected Lewis acidity, Li+>Na+>K+. Importantly, the reactivity pattern can be drastically changed by adding ligands and additives. Kinetic, labelling, and competition experiments as well as DFT calculations suggested that the reaction proceeds through a concerted direct hydride-transfer mechanism, originally suggested by Woodward. The lithium cation was found to be intrinsically more active than heavier congeners, but in the case of aryl ketones a decrease in reaction rate was observed at ≈40 percent conversion with lithium cations. Noncovalent-interaction analysis revealed that this deceleration effect originated from specific noncovalent interactions between the aryl moiety of 1-phenylethanol and the carbonyl group of acetophenone, which stabilize the product in the coordination sphere of lithium and thus poison the catalyst. The ligand/additive effect is a complicated phenomenon that includes a combination of several factors, such as the decrease of activation energy by ligation (confirmed by distortion/interaction calculations of N,N,N’,N’-tetramethylethylenediamine, TMEDA) and the change in relative stabilization of reagents and substrates in the solution and the coordination sphere of the metal. Finally, we observed that lithium-base-catalyzed transfer hydrogenation can be further facilitated by the addition of an inexpensive and benign reagent, LiCl, which likely operates by re-initiating the reaction on a new lithium center.
Tunable System for Electrochemical Reduction of Ketones and Phthalimides
Chen, Gong,Qiao, Tianjiao,Wang, Yaxin,Zhang, Jian,Zhao, Jianyou
supporting information, p. 3297 - 3302 (2021/10/14)
Herein, we report an efficient, tunable system for electrochemical reduction of ketones and phthalimides at room temperature without the need for stoichiometric external reductants. By utilizing NaN3 as the electrolyte and graphite felt as both the cathode and the anode, we were able to selectively reduce the carbonyl groups of the substrates to alcohols, pinacols, or methylene groups by judiciously choosing the solvent and an acidic additive. The reaction conditions were compatible with a diverse array of functional groups, and phthalimides could undergo one-pot reductive cyclization to afford products with indolizidine scaffolds. Mechanistic studies showed that the reactions involved electron, proton, and hydrogen atom transfers. Importantly, an N3/HN3 cycle operated as a hydrogen atom shuttle, which was critical for reduction of the carbonyl groups to methylene groups.
Amino Acid-Functionalized Metal-Organic Frameworks for Asymmetric Base–Metal Catalysis
Newar, Rajashree,Akhtar, Naved,Antil, Neha,Kumar, Ajay,Shukla, Sakshi,Begum, Wahida,Manna, Kuntal
supporting information, p. 10964 - 10970 (2021/03/29)
We report a strategy to develop heterogeneous single-site enantioselective catalysts based on naturally occurring amino acids and earth-abundant metals for eco-friendly asymmetric catalysis. The grafting of amino acids within the pores of a metal-organic framework (MOF), followed by post-synthetic metalation with iron precursor, affords highly active and enantioselective (>99 % ee for 10 examples) catalysts for hydrosilylation and hydroboration of carbonyl compounds. Impressively, the MOF-Fe catalyst displayed high turnover numbers of up to 10 000 and was recycled and reused more than 15 times without diminishing the enantioselectivity. MOF-Fe displayed much higher activity and enantioselectivity than its homogeneous control catalyst, likely due to the formation of robust single-site catalyst in the MOF through site-isolation.
