- Benzyl C–O and C–N Bond Construction via C–C Bond Dissociation of Oxime Ester under Visible Light Irradiation
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A photoredox benzyl activation was developed via formidable C(sp3)–C(sp3) bond dissociation of 1-aryl acetone oxime esters, which were easily prepared from benzyl ketones. Further coupling with O- and N- nucleophiles successfully forged important benzyl ether and amines derivatives in one pot. In this process, different substitutions on oxime esters were found compatible and various primary and secondary alcohols and amines, as well as amides showed good performance as nucleophiles. Mechanistic studies by control experiments, electrochemical measurements and in-situ NMR spectra proposed a N–O bond interruption/C–C bond fragmentation/oxidation sequence to provide the key cation intermediate for the next electrophilic SN process. The features of mild condition, short reaction time and broad substrate scope made this new strategy much promising in the transformation of benzyl compounds, which might be valuable in last-stage functionalizations.
- Fan, Xiuwei,Lei, Tao,Liu, Zan,Yang, Xiu-Long,Cheng, Yuan-Yuan,Liang, Ge,Chen, Bin,Tung, Chen-Ho,Wu, Li-Zhu
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p. 1551 - 1558
(2019/09/09)
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- Metal Free, Direct and Selective Deoxygenation of α-Hydroxy Carbonyl Compounds: Access to α,α-Diaryl Carbonyl Compounds
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An efficient, metal free, direct and selective deoxygenation of α-hydroxy carbonyl compounds is achieved with the aid of catalytic amount of aqueous HClO4 (70 %) and triethylsilane as hydride source. A variety of α-hydroxy-α,α-diaryl carbonyl compounds are selectively deoxygenated to give α,α-diaryl carbonyl compounds in good to excellent yields. Intermediacy of α-keto carbenium ion is proposed on the basis of some control experiments and atmospheric pressure chemical ionization mass spectral analysis.
- Kumar, Anil,Sandeep,Venugopalan, Paloth
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- Ni-Catalyzed Reductive C-O Bond Arylation of Oxalates Derived from α-Hydroxy Esters with Aryl Halides
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A Ni-catalyzed reductive cross-coupling of α-hydroxycarbonyl compounds modified with oxalyl groups and aryl halides has been developed that furnishes α-aryl esters under mild conditions and tolerates a variety of functionalized aryl halides bearing electron-withdrawing and -donating groups. This work highlights C-O bond fragmentation on secondary alkyl carbon centers that generates α-carbonyl radicals.
- Gao, Mengyu,Sun, Deli,Gong, Hegui
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supporting information
p. 1645 - 1648
(2019/03/11)
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- Two efficient pathways for the synthesis of aryl ketones catalyzed by phosphorus-free palladium catalysts
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Allylic alcohols, 1-buten-3-ol, 1-penten-3-ol and 1-octen-3-ol, reacted with aryl iodides (iodotoluene, 4-iodotoluene, 4-iodophenol and 4-iodanisole) under Heck reaction conditions to form corresponding saturated aryl ketones in one step. The same products were obtained in a two-step tandem reaction consisted of the Heck coupling of allylic alcohols with aryl iodides, followed by hydrogenation. Reactions were catalyzed by phosphorus-free palladium precursors modified with the menthol-substituted imidazolium chlorides. Formation of crystalline palladium nanoparticles, of the diameter up to 65 nm, in the reaction mixture was evidenced by TEM.
- Wirwis,Feder-Kubis,Trzeciak
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- Regioselective 1,2-Diol Rearrangement by Controlling the Loading of BF3·Et2O and Its Application to the Synthesis of Related Nor-Sesquiterene- and Sesquiterene-Type Marine Natural Products
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The regiocontrolled rearrangement of 1,2-diols has been achieved by controlling the loading of BF3·Et2O. Its applicability is showcased by the divergent synthesis of austrodoral, austrodoric acid, and 8-epi-11-nordriman-9-one, as well as a formal synthesis of siphonodictyal B and liphagal. A new light is shed on piancol-type rearrangements that will be useful in diversity-oriented synthesis of related natural products.
- Wang, Jun-Li,Li, Hui-Jing,Wang, Hong-Shuang,Wu, Yan-Chao
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supporting information
p. 3811 - 3814
(2017/07/26)
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- Dynamic Reductive Kinetic Resolution of Benzyl Ketones using Alcohol Dehydrogenases and Anion Exchange Resins
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Dynamic reductive kinetic resolutions of racemic 3-arylalkanones have been performed by the proper combination of an alcohol dehydrogenase and a basic anionic resin. The best results were found for the bioreduction with the alcohol dehydrogenase type A from Rhodococcus ruber DSM 44541 overexpressed in Escherichia coli (E. coli/ADH-A) and the commercially available evo-1.1.200, while the Amberlite IRA-440 C and the DOWEX-MWA-1 resins allowed efficient in situ racemizations. Reaction conditions were optimized in terms of enzyme source and loading, type and amount of resin, pH, temperature and reaction times, obtaining a series of (R,R)-substituted propan-2-ols with good conversions and both diastereoselectivity and stereoselectivity. As a proof of concept, the subsequent intramolecular cyclization of a selected propan-2-ol substrate afforded a valuable isochroman heterocycle without any loss of the optical purity.
- Méndez-Sánchez, Daniel,Mangas-Sánchez, Juan,Busto, Eduardo,Gotor, Vicente,Gotor-Fernández, Vicente
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p. 122 - 131
(2016/01/25)
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- Control of the Chemoselectivity of Metal N-Aryl Nitrene Reactivity: C-H Bond Amination versus Electrocyclization
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A mechanism study to identify the elements that control the chemoselectivity of metal-catalyzed N-atom transfer reactions of styryl azides is presented. Our studies show that the proclivity of the metal N-aryl nitrene to participate in sp3-C-H bond amination or electrocyclization reactions can be controlled by either the substrate or the catalyst. Electrocyclization is favored for mono-β-substituted and sterically noncongested styryl azides, whereas sp3-C-H bond amination through an H-atom abstraction-radical recombination mechanism is preferred when a tertiary allylic reaction center is present. Even when a weakened allylic C-H bond is present, our data suggest that the indole is still formed through an electrocyclization instead of a common allyl radical intermediate. The site selectivity of metal N-aryl nitrenes was found to be controlled by the choice of catalyst: Ir(I)-alkene complexes trigger electrocyclization processes while Fe(III) porphyrin complexes catalyze sp3-C-H bond amination in substrates where Rh2(II) carboxylate catalysts provide both products.
- Kong, Chen,Jana, Navendu,Jones, Crystalann,Driver, Tom G.
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supporting information
p. 13271 - 13280
(2016/10/22)
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- Ruthenium(IV) porphyrin catalyzed highly selective oxidation of internal alkenes into ketones with Cl2pyNO as terminal oxidant
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A new method for the conversion of internal alkenes into ketones without cleavage of CC bond by using dichlororuthenium(IV) meso-tetrakis(2,6- dichlorophenyl)porphyrin [RuIV(TDCPP)Cl2] as catalyst and 2,6-dichloropyridine N-oxide(Cl2pyNO) as oxidant is developed.
- Wang, Zhi-Ming,Sang, Xue-Ling,Che, Chi-Ming,Chen, Jian
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supporting information
p. 1736 - 1739
(2014/03/21)
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- Origin of regioselectivity in the reactions of nitronate and enolate ambident anions
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The reactions of nitronates of ring-substituted phenylnitromethanes and enolates of ring-substituted 1-phenyl-2-propanones with MeOBs gave exclusively the O-methylated and C-methylated products, respectively. DFT calculations suggested that two factors, n
- Sakata, Tomomi,Seki, Natsuko,Yomogida, Kozue,Yamagishi, Hiroko,Otsuki, Akino,Inoh, Chie,Yamataka, Hiroshi
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p. 10738 - 10744
(2013/02/25)
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- Unexpected extension of usage of PPh3/CBr4, a versatile reagent: Isomerization of aromatic allylic alcohols
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The PPh3/CBr4-catalyzed isomerization of 2-aromatic allylic alcohols into the corresponding saturated aldehydes or ketones has been achieved at room temperature in good to excellent yields under mild and metal-free conditions. This new methodology has been applied successfully to the synthesis of ibuprofen in four steps.
- Gong, Wanchun,Liu, Yun,Xue, Jijun,Xie, Zhixiang,Li, Ying
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p. 1597 - 1599
(2013/02/23)
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- Baeyer-Villiger monooxygenase-catalyzed kinetic resolution of racemic α-alkyl benzyl ketones: enzymatic synthesis of α-alkyl benzylketones and α-alkyl benzylesters
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The application of three BVMOs for the enantioselective oxidation of 3-phenylbutan-2-ones with different substituents in the aromatic moiety is described. By choosing the appropriate biocatalyst and substrate combination, chiral ketones and esters can be obtained with excellent enantiopurities. This methodology could also be applied to the resolution of racemic α-alkyl benzylketones with longer alkyl chains as well as with two substituted α-substituted benzylacetones. A kinetic analysis revealed that the BVMOs studied effectively convert all tested compounds showing that the enzymes are tolerant towards the substrate structure while being highly enantioselective. These properties render BVMOs as valuable biocatalysts for the preparation of compounds with high interest in organic synthesis.
- Rodriguez, Cristina,Gonzalo, Gonzalo de,Torres Pazmino, Daniel E.,Fraaije, Marco W.,Gotor, Vicente
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experimental part
p. 1168 - 1173
(2009/10/02)
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- Arenediazonium o-benzenedisulfonimides in Heck-type arylation of allylic alcohols
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Arenediazonium o-benzenedisulfonimides were reacted with primary and secondary allylic alcohols. The reactions, carried out in aqueous ethanol in the presence of palladium(II) acetate as precatalyst and sodium hydrogen carbonate as base, gave the arylation products with good overall conversion. In all cases, the major products were the β-arylated carbonyl derivatives. The o-benzene-disulfonimide was recovered in high yield from all the reactions, and it was recycled for the preparation of other salts. Georg Thieme Verlag Stuttgart.
- Barbero, Margherita,Cadamuro, Silvano,Dughera, Stefano
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p. 3443 - 3452
(2008/02/12)
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- Use of conjugated dienones in cyclialkylations: Total syntheses of arucadiol, 1,2-didehydromiltirone, (±)-hinokione, (±)-nimbidiol, sageone, and miltirone
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Functionalized hydrophenanthrenes can be prepared using a cyclialkylation-based strategy. These annulations are highly dependent on the directing effects of the arene substitutents and on conformational considerations. The utility of this methodology was featured in the syntheses of six diterpenoids.
- Majetich, George,Liu, Shuang,Fang, Jing,Siesel, David,Zhang, Yong
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p. 6928 - 6951
(2007/10/03)
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- Intramolecular aryl rearrangement in the photolysis of alken-1-yl aryl methyl phosphates
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Upon UV-irradiation of alken-1-yl aryl methyl phosphates in methanol a cationic migration of an aryl group to a neighbouring olefinic moiety to produce arylalkanone and arylalken-1-yl methyl ether has been observed.
- Nakamura, Mitsunobu,Okamoto, Yoshiki,Takamuku, Setsuo
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p. 209 - 210
(2007/10/03)
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- Nickel-catalyzed direct electrochemical cross-coupling between aryl halides and activated alkyl halides
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The electrochemical reduction of a mixture of aryl halides and activated alkyl halides in DMF in the presence of catalytic amount of NiBr2bipy leads to cross-coupling products in good to high yields. The method applies to the synthesis of α-aryl ketones, α-aryl esters, and allylated compounds from readily available organic halides. Optimization of the process has been obtained by slowly adding the most reactive organic halide (usually the activated alkyl halide) during the electrolysis which is best conducted at 70 °C when aryl bromides are involved.
- Durandetti, Muriel,Nedelec, Jean-Yves,Perichon, Jacques
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p. 1748 - 1755
(2007/10/03)
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- A novel method of arylation of α-chloroketones
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α-Arylated ketones were obtained in moderate to good yields by one-step electroreductive coupling of α-chloroketones and arylhalides in DMF and in the presence of a Al- or Zn-sacrificial anode and a catalytic amount of a nickel complex.
- Durandetti,Sibille,Nedelec,Perichon
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p. 145 - 151
(2007/10/02)
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- New Method for Generation of β-Oxido Carbenoid via Ligand Exchange Reaction of Sulfoxides: A Versatile Procedure for One-Carbon Homologation of Carbonyl Compounds
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A new procedure for one-carbon homologation of carbonyl compounds is described.The method is based on the rearrangement of β-oxido carbenoid which is generated via the ligand exchange reaction of the sulfinyl group of α-chloro β-hydroxy sulfoxide with tert-butyllithium.Addition of the carbanion of aryl 1-chloroalkyl sulfoxides to carbonyl compounds gave the adducts in good yields.The β-oxido carbenoid rearrangement of the adducts gave one-carbon homologated carbonyl compounds having an α-alkyl substituent.A similar reaction of the adducts derived from carbonyl compounds with chloromethyl p-tolyl sulfoxide yielded a procedure for a methylene insertion.The stereochemistry of the β-oxido carbenoid rearrangenment is also discussed.
- Satoh, Tsuyoshi,Itoh, Norifumi,Gengyo, Kaoru,Takada, Sae,Asakawa, Naoyuki,et al.
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p. 11839 - 11852
(2007/10/02)
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- Photochemical reactivity of α-phenyl β,γ-enones. Singlet 1,3-acyl shift, triplet aromatic di-?-methane (DPM) rearrangement and triplet aryl-carbonyl bridging
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The photochemistry of the series of α-phenyl β,γ-enones 6-10 has been studied under conditions of both direct (λ 300 nm) and triplet-sensitized irradiation with the aim of determining the reactivity patterns of these "multi"-chromophoric systems.Upon direct irradiation, the reactants exhibit the typical photoreactions of β,γ-enones, viz. the 1,3-acyl shift, affording the corresponding (E)- and (Z)-5-phenyl-4-hexen-3-ones, decarbonylation of the radicals formed by α-cleavage and recombination of the resulting alkyl radicals and, in addition, a new type of reaction from the triplet-excited state yielding small amounts of the corresponding acetophenones.The acetophenones are thought to be formed by initial β-bridging between the carbonyl and the phenyl group, followed by extrusion of the C4H6 fragment from the 1,4- or 1,3-oxa-diradical.Upon sensitized irradiation, the o-methoxy- and p-cyano-substituted reactants 9 and 10 exhibit the di-?-methane rearrangement, leading to mixtures of the corresponding cis- and trans-1-acetyl-1-methyl-2-phenylcyclopropanes, with quantum yields of 0.03 and 0.10, respectively.The formation of the 1,3-AS and decarbonylation products illustrates the occurrence of α-cleavage, whereas the acetophenones and di-?-methane products are formed via initial aryl-carbonyl and aryl-vinyl bridging, respectively.The inability of the other α-phenyl β,γ-enones to undergo photocyclopropanation is discussed in terms of excitation-energy partition.In the o-methoxy and p-cyano-substituted reactants, the excitation energy may be predominantly concentrated in the aryl moiety in contrast to the other two systems in which the excitation energy may be mainly localized on the β,γ-enone moiety.Subsequent triplet-energy dissipation by a free-rotor mechanism would then account for the stability of these systems.This was observed for (E)-7 which, upon triplet sensitization, affords only the (Z) isomer, whereas this process is degenerate for the other substrates studied.
- Koppes, Margareth J. C. M.,Beentjes, Peter C. J.,Cerfontain, Hans
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p. 313 - 324
(2007/10/02)
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- The Allopolarization Principle and its Applications, VI. The Alkylation of Enolate Anions: Polarity and Regioselectivity
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The O/C methylation ratio in the reaction of sodium enolates with dimethylsulfate depends on the polar (electronic) effect of substituents.The relative ?-charge density Px/y = lx/ly can be used as a measure for the polarity of ambifunctional anions; in case of enolate anions PO/C = lO/lC.The change of the regioselectivity Sf = log QO/QC in the alkylation of enolates is a function of a change in the polarity PO/C; ΔSf=f(ΔPx/y).The polar effect of substituents influences the charge control during the alkylation process via a change of the polarity of the enolate system: The higher the polarity of the anion, the stronger the charge control and the higher the yield of enol ether (O-alkylation). - Keywords: Alkylation, Enolate Anions
- Gompper, Rudolf,Vogt, Hans-Hubert,Wagner, Hans-Ulrich
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p. 1644 - 1652
(2007/10/02)
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- The Allopolarization Principle and its Applications, IV. Substituent Effects in the Methylation of Enolate Anions
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The ratio of O- and C-methylated products in the reaction of the sodium salts of acetophenones 1, propiophenones 3, phenylacetones 5, β-dicarbonyl compounds 12, α-cyanocarbonyl compounds 13, acetaldehyde, propionaldehyde, and diethylketone with dimethyl sulfate, methyl iodide, and trimethyl phosphate in HMPTA has been determined with regard to the effect of substituents.In some cases the influence of solvents, concentration and temperature has also been studied.
- Gompper, Rudolf,Vogt, Hans-Hubert
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p. 2866 - 2883
(2007/10/02)
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