1737-19-5Relevant academic research and scientific papers
Markovnikov Wacker-Tsuji Oxidation of Allyl(hetero)arenes and Application in a One-Pot Photo-Metal-Biocatalytic Approach to Enantioenriched Amines and Alcohols
Albarrán-Velo, Jesús,Gotor-Fernández, Vicente,Lavandera, Iván
, p. 4096 - 4108 (2021/08/19)
The Wacker-Tsuji aerobic oxidation of various allyl(hetero)arenes under photocatalytic conditions to form the corresponding methyl ketones is presented. By using a palladium complex [PdCl2(MeCN)2] and the photosensitizer [Acr-Mes]ClO4 in aqueous medium and at room temperature, and by simple irradiation with blue led light, the desired carbonyl compounds were synthesized with high conversions (>80%) and excellent selectivities (>90%). The key process was the transient formation of Pd nanoparticles that can activate oxygen, thus recycling the Pd(II) species necessary in the Wacker oxidative reaction. While light irradiation was strictly mandatory, the addition of the photocatalyst improved the reaction selectivity, due to the formation of the starting allyl(hetero)arene from some of the obtained by-products, thus entering back in the Wacker-Tsuji catalytic cycle. Once optimized, the oxidation reaction was combined in a one-pot two-step sequential protocol with an enzymatic transformation. Depending on the biocatalyst employed, i. e. an amine transaminase or an alcohol dehydrogenase, the corresponding (R)- and (S)-1-arylpropan-2-amines or 1-arylpropan-2-ols, respectively, could be synthesized in most cases with high yields (>70%) and in enantiopure form. Finally, an application of this photo-metal-biocatalytic strategy has been demonstrated in order to get access in a straightforward manner to selegiline, an anti-Parkinson drug. (Figure presented.).
Nickel-Catalyzed Mono-Selective α-Arylation of Acetone with Aryl Chlorides and Phenol Derivatives
Amgoune, Abderrahmane,Derhamine, Sary Abou,Krachko, Tetiana,Monteiro, Nuno,Pilet, Guillaume,Schranck, Johannes,Tlili, Anis
supporting information, p. 18948 - 18953 (2020/09/01)
The challenging nickel-catalyzed mono-α-arylation of acetone with aryl chlorides, pivalates, and carbamates has been achieved for the first time. A nickel/Josiphos-based catalytic system is shown to feature unique catalytic behavior, allowing the highly selective formation of the desired mono-α-arylated acetone. The developed methodology was applied to a variety of (hetero)aryl chlorides including biologically relevant derivatives. The methodology has been extended to the unprecedented coupling of acetone with phenol derivatives. Mechanistic studies allowed the isolation and characterization of key Ni0 and NiII catalytic intermediates. The Josiphos ligand is shown to play a key role in the stabilization of NiII intermediates to allow a Ni0/NiII catalytic pathway. Mechanistic understanding was then leveraged to improve the protocol using an air-stable NiII pre-catalyst.
Porphyrins as Photoredox Catalysts in Csp2-H Arylations: Batch and Continuous Flow Approaches
De Souza, Aline A. N.,Silva, Nathalia S.,Müller, Andressa V.,Polo, André S.,Brocksom, Timothy J.,De Oliveira, Kleber T.
, p. 15077 - 15086 (2019/01/03)
We have investigated both batch and continuous flow photoarylations of enol-acetates to yield different α-arylated aldehyde and ketone building blocks by using diazonium salts as the aryl-radical source. Different porphyrins were used as SET photocatalysts, and photophysical as well as electrochemical studies were performed to rationalize the photoredox properties and suggest mechanistic insights. Notably, the most electron-deficient porphyrin (meso-tetra(pentafluorophenyl)porphyrin) shows the best photoactivity as an electron donor in the triplet excited state, which was rationalized by the redox potentials of excited states and the turnover of the porphyrins in the photocatalytic cycle. A two-step continuous protocol and multigram-scale reactions are also presented revealing a robust, cost-competitive, and easy methodology, highlighting the significant potential of porphyrins as SET photocatalysts.
Pinacolatoboron fluoride (pinBF) is an efficient fluoride transfer agent for diastereoselective synthesis of benzylic fluorides
Cresswell, Alexander J.,Davies, Stephen G.,Figuccia, Aude L.A.,Fletcher, Ai M.,Heijnen, Dorus,Lee, James A.,Morris, Melloney J.,Kennett, Alice M.R.,Roberts, Paul M.,Thomson, James E.
, p. 3373 - 3377 (2015/06/02)
The incorporation of alkoxy ligands within a range of alkoxyfluoroboranes and dialkoxyfluoroboranes results in fluoroborane reagents with attenuated Lewis acidity and increased ability to donate fluoride ion(s) when compared to boron trifluoride itself. Pinacolatoboron fluoride (pinBF), prepared in situ from BF3·OEt2 and bis(O-trimethylsilyl)pinacol, has been identified as an efficient fluoride donor which allows highly stereoselective SN1-type epoxide ring-opening (with retention of configuration) of a range of trans-β-methyl-substituted aryl epoxides to give the corresponding syn-fluorohydrins. The substrate scope of this transformation is more broad than the analogous protocol using boron trifluoride alone.
COMPOUND HAVING BRANCHED ALKYL OR BRANCHED ALKENYL, OPTICALLY ISOTROPIC LIQUID CRYSTAL MEDIUM AND OPTICAL ELEMENT
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Paragraph 0322; 0330; 0331, (2013/05/09)
The first object of the invention is to provide a liquid crystal compound that is stable to heat, light and so on, and has a large optical anisotropy, a large dielectric anisotropy and a low melting point. The second object is to provide a liquid crystal medium that is stable to heat, light and so on, has a broad temperature range of a liquid crystal phase, a large optical anisotropy and a large dielectric anisotropy, and exhibits an optically isotropic liquid crystal phase. The third object is to provide a variety of optical elements containing the liquid crystal medium, which can be used in a broad temperature range and has a short response time, a high contrast and a low driving voltage. A liquid crystal compound with branched alkyl or branched alkenyl as represented by formula (1), a liquid crystal medium (a liquid crystal composition or a polymer/liquid crystal composite material) containing the liquid crystal compound, and an optical element containing the liquid crystal medium are described. In formula (1), R1 is branched alkyl of C3-20 or branched alkenyl of C3-20. The ring A1, A2, A3, A4 or A5 is 1,4-phenylene or 1,3-dioxane-2,5-diyl, for example. Z1, Z2, Z3 and Z4 are independently a single bond or C1-4 alkylene, for example. Y1 is fluorine, for example, m, n and p are independently 0 or 1, and 1≤m+n+p≤3.
Palladium-catalyzed mono-α-arylation of acetone with aryl imidazolylsulfonates
Ackermann, Lutz,Mehta, Vaibhav P.
supporting information; experimental part, p. 10230 - 10233 (2012/09/22)
Set the ace(tone): A palladium catalyst derived from the bidentate XantPhos ligand and Pd(OAc)2 has enabled broadly applicable mono-α-arylations of acetone to be performed with air- and moisture-stable aryl imidazolylsulfonates as most user-friendly electrophiles (see scheme). Copyright
Palladium-catalyzed mono-α-arylation of acetone with aryl halides and tosylates
Hesp, Kevin D.,Lundgren, Rylan J.,Stradiotto, Mark
supporting information; experimental part, p. 5194 - 5197 (2011/06/10)
We report the first example of selective Pd-catalyzed mono-α- arylation of acetone employing aryl chlorides, bromides, iodides, and tosylates. The use of appropriately designed P,N-ligands proved to be the key to controlling the reactivity and selectivity. The reaction affords good yields with substrates containing a range of functional groups at modest Pd loadings using Cs2CO3 as the base and employing acetone as both a reagent and the solvent.(Figure Presented)
β-fluoroamphetamines via the stereoselective synthesis of benzylic fluorides
Cresswell, Alexander J.,Davies, Stephen G.,Lee, James A.,Roberts, Paul M.,Russell, Angela J.,Thomson, James E.,Tyte, Melloney J.
supporting information; experimental part, p. 2936 - 2939 (2010/09/10)
A range of substituted aryl epoxides undergo efficient ring-opening hydrofluorination upon treatment with 0.33 equiv of BF3-OEt 2 in CH2Cl2 at -20 -°C to give the corresponding syn-fluorohydrins, consistent with a mechanism involving a stereoselective SN1-type epoxide ring-opening process. The benzylic fluoride products of these reactions are valuable templates for further elaboration, as demonstrated by the preparation of a range of aryl-substituted β-fluoroamphetamines.
Mass spectrometric investigations on phenylacetic acid derivatives, IV: Loss of ortho-substituents from ionized phenyl-2-propanones upon electron impact
Striegel,Mayer,Wiegrebe,Schlunegger,Siegrist,Aebi
, p. 751 - 760 (2007/10/02)
In the gas phase, the phenyl-2-propanone molecules 2a-4a lose upon electron impact chloro-, bromo-, and iodo-radicals specifically at the orthopOsition of the phenyl group giving rise to strong (M-Hal.)+-ions (70/12 eV; 1st and 2nd FFR) of identical structure as confirmed by their MIKE-CAD-spectra. The daughter ions at m/z 133 from o-chlorophenyl-2-propanone (2a) and 2,2-dimethyl-2,3-dihydro[b]furane (11) are structurally similar but not identical (similarity index 99.8). The collisionally activated (2nd FFR) (M-Br.)+-ions from o-bromophenyl-2-propanone (3a) and 1-bromo-1-phenyl-2-propanone (12) produce virtually congruent spectra. The most impOrtant subsequent fragmentation of the (M-Hal-)+-ions from 2a-4a is the loss of CO which incorporates the C-atom of the carbonyl group exclusively (13C labelling). Mechanistic aspects of the fragmentation sequences are discussed (Figs. 5 and 8).
ELECTRFLUORATION EN POSITION BENZYLIQUE DANS LE SULFOLANE
Laurent, Eliane,Marquet, Bernard,Tardivel, Robert
, p. 115 - 126 (2007/10/02)
The use of sulfolane as a solvent instead of acetonitrile in the electrofluorination of benzylic derivatives 1, (R=H, Cl) gives greater yields of benzylic fluorides 2, since the formation of acetamide byproducts 4 is prevented.However, the parallel fluorination of the aromatic nucleus is not avoided under these conditions.
