- Selective Palladium-Catalyzed α,β-Homodiarylation of Vinyl Esters in Aqueous Medium
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A palladium-catalyzed 1,2-diarylation of vinyl esters with arylboronic acids in water has been developed. This newly elaborated protocol features a good functional group tolerance and provides one-step access to 1,2-diarylethanol derivatives under mild reaction conditions. The presented reaction can be carried out in the water at ambient temperature without the addition of any ligands, what makes this procedure environmentally benign. The transformation occurs within a single catalytic cycle and is feasible due to the modification of transition metal catalytic activity through the influence of π-acceptor olefin (benzoquinone) as well as water as a medium. Moreover, this protocol allows to generate entire compound libraries (highly profitable in medicinal chemistry) and utilizes sustainable arylboronic acids as coupling partners under mild conditions. It is also noted that the structure of boron moiety has a great impact on the reaction selectivity, the usage of sterically hindered esters of arylboronic acids influence the reaction course towards stilbenes.
- Brodzka, Anna,Koszelewski, Dominik,Ostaszewski, Ryszard,Trzepizur, Damian,Wilk, Monika
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supporting information
p. 6028 - 6036
(2021/12/10)
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- Photoredox-Catalyzed Benzylic Esterification via Radical-Polar Crossover
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Photoredox-catalyzed C-O bond formation reactions are reported. The decarboxylative esterification reaction allows the conversion of a variety of arylacetic acids into the corresponding benzyl carboxylates. Furthermore, the use of (diacetoxyiodo)benzene allows the conversion of the benzylic C-H bond through hydrogen atom transfer. The reactions were applied to the divergent transformation of pharmaceuticals via decarboxylative or C-H esterification reactions.
- Maeda, Bumpei,Sakakibara, Yota,Murakami, Kei,Itami, Kenichiro
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supporting information
p. 5113 - 5117
(2021/07/19)
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- Selective benzylic C–H monooxygenation mediated by iodine oxides
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A method for the selective monooxdiation of secondary benzylic C–H bonds is described using an N-oxyl catalyst and a hypervalent iodine species as a terminal oxidant. Combinations of ammonium iodate and catalytic N-hydroxyphthalimide (NHPI) were shown to be effective in the selective oxidation of n-butylbenzene directly to 1-phenylbutyl acetate in high yield (86%). This method shows moderate substrate tolerance in the oxygenation of substrates containing secondary benzylic C–H bonds, yielding the corresponding benzylic acetates in good to moderate yield. Tertiary benzylic C–H bonds were shown to be unreactive under similar conditions, despite the weaker C–H bond. A preliminary mechanistic analysis suggests that this NHPI-iodate system is functioning by a radical-based mechanism where iodine generated in situ captures formed benzylic radicals. The benzylic iodide intermediate then solvolyzes to yield the product ester.
- LaMartina, Kelsey B.,Kuck, Haley K.,Oglesbee, Linda S.,Al-Odaini, Asma,Boaz, Nicholas C.
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supporting information
p. 602 - 609
(2019/04/17)
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- Expanding the Substrate Specificity of Thermoanaerobacter pseudoethanolicus Secondary Alcohol Dehydrogenase by a Dual Site Mutation
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Here, we report the asymmetric reduction of selected phenyl-ring-containing ketones by various single- and dual-site mutants of Thermoanaerobacter pseudoethanolicus secondary alcohol dehydrogenase (TeSADH). The further expansion of the size of the substrate binding pocket in the mutant W110A/I86A not only allowed the accommodation of substrates of the single mutants W110A and I86A within the expanded active site but also expanded the substrate range of the enzyme to ketones bearing two sterically demanding groups (bulky–bulky ketones), which are not substrates for the TeSADH single mutants. We also report the regio- and enantioselective reduction of diketones with W110A/I86A TeSADH and single TeSADH mutants. The double mutant exhibited dual stereopreference to generate the Prelog products most of the time and the anti-Prelog products in a few cases.
- Musa, Musa M.,Bsharat, Odey,Karume, Ibrahim,Vieille, Claire,Takahashi, Masateru,Hamdan, Samir M.
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p. 798 - 805
(2018/02/21)
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- Oxidation of alkylarenes by nitrate catalyzed by polyoxophosphomolybdates: Synthetic applications and mechanistic insights
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Alkylarenes were catalytically and selectively oxidized to the corresponding benzylic acetates and carbonyl products by nitrate salts in acetic acid in the presence of Keggin type molybdenum-based heteropolyacids, H3+xPVxMo12-xO40 (x = 0-2). H 5PV2Mo10O40 was especially effective. For methylarenes there was no over-oxidation to the carboxylic acid contrary to what was observed for nitric acid as oxidant. The conversion to the aldehyde/ketone could be increased by the addition of water to the reaction mixture. As evidenced by IR and 15N NMR spectroscopy, initially the nitrate salt reacted with H5PV2Mo10O 40 to yield a NVO2+[H 4PV2Mo10O40] intermediate. In an electron-transfer reaction, the proposed NVO2 +[H4PV2Mo10O40] complex reacts with the alkylarene substrate to yield a radical-cation-based donor-acceptor intermediate, NIVO2[H4PV 2Mo10O40]-ArCH2R+.. Concurrent proton transfer yields an alkylarene radical, ArCHR., and NO2. Alternatively, it is possible that the NVO 2+[H4PV2Mo10O 40] complex abstracts a hydrogen atom from alkylarene substrate to directly yield ArCHR. and NO2. The electron transfer-proton transfer and hydrogen abstraction scenarios are supported by the correlation of the reaction rate with the ionization potential and the bond dissociation energy at the benzylic positions of the alkylarene, respectively, the high kinetic isotope effect determined for substrates deuterated at the benzylic position, and the reaction order in the catalyst. Product selectivity in the oxidation of phenylcyclopropane tends to support the electron transfer-proton transfer pathway. The ArCHR. and NO2 radical species undergo heterocoupling to yield a benzylic nitrite, which undergoes hydrolysis or acetolysis and subsequent reactions to yield benzylic acetates and corresponding aldehydes or ketones as final products.
- Khenkin, Alexander M.,Neumann, Ronny
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p. 6356 - 6362
(2007/10/03)
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- Substituent Effect Studies of Aryl-Assisted Solvolyses. I. The Acetolysis of 2,2-Bis(substituted phenyl)ethyl p-Toluenesulfonates
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The substituent effect on the acetolysis of 2,2-bis(substituted phenyl)ethyl p-toluenesulfonates at 90.10 deg C can be described accurately in terms of the Yukawa-Tsuno (LArSR) relationship, giving a ρ value of -4.44 and an r value of 0.53. The substituent effect correlation of this system carrying two aryls is quite comparable to that of the 2-methyl-2-phenylpropyl system carrying a single aryl group, suggesting the close similarity in the structure of the transition states between the systems. The results can be reasonably accounted for on the basis of the accepted mechanism of this reaction, involving a rate-determining aryl-assisted transition state where only one aryl group of the two β-aryl groups participates.
- Fujio, Mizue,Maeda, Yasuyuki,Goto, Mutsuo,Saeki, Yoshihiro,Mishima, Masaaki,Tsuno, Yuho
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p. 3015 - 3020
(2007/10/02)
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- Substituent Effect Studies of Aryl-Assisted Solvolyses. II. The Acetolysis of 2-Phenyl-2-(substituted phenyl)ethyl p-Toluenesulfonates
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The substituent effect on the acetolysis of 2-phenyl-2-(substituted phenyl)ethyl p-toluenesulfonates had a nonlinear LArSR correlation and was explicable in terms of a competitive aryl-assisted mechanism involving the X-substituted phenyl-assisted (kXM) pathway and the unsubstituted phenyl-assisted (kXN) pathway. By the application of the iterative nonlinear least-squares method based on the LArSR Eq., the substituent effect on the overall kt was dissected into the best-fit kM correlation of ρM=-3.53 with rM=0.60, and the kN correlation of ρN=-0.88 with ?0. The ρM and rM values for the effects of assisting aryl substituents are quite close to those of the 2-methyl-2-phenylpropyl system and the small ρN value with unexalted ?0 constant for the unassisting aryls is compatible to the remote β-aryl effect. The relative rates of competing pathways dissected based on the substituent effect analysis agreed completely with the ratio of respective aryl migration products determined by the 13C-tracer method. Exact rate-product correlation demonstrates that this system involves two discrete aryl-assisted pathways, kXM and kXN, which do not cross over.
- Fujio, Mizue,Maeda, Yasuyuki,Goto, Mutsuo,Saeki, Yoshihiro,Mishima, Masaaki,Tsuno, Yuho
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p. 3021 - 3029
(2007/10/02)
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- A novel synthesis of esters via substitution of the benzotriazolyl group in 1-(benzotriazol-1-yl)alkyl esters with organozinc reagents
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Aldehydes are converted by thionyl chloride and benzotriazole into 1-(1-chloroalyl)benzotriazoles which react with sodium carboxylates to give 1-(benzotriazol-1-yl)alkyl esters. 3. In the alternative route, 3 are prepared by substitution of one of the acetoxy groups in acylals with benzotriazole. The benzotriazolyl moiety in 3 is substituted by an alkyl, an aryl or an alkynyl group upon treatment with an organic reagent in a new versatile synthesis of esters 4.
- Katritzky,Rachwal,Rachwal
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- Benzotriazole: A novel synthetic auxiliary
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Benzotriazole and aldehydes react reversibly to give addition products: in the presence of amines and other NH-compounds water can be eliminated to form products of type Bt-CHR-NR′R″. The latter are versatile intermediates for the preparation of primary, secondary, and tertiary amines and in the alkylation of hydroxylamines, hydrazines, amides, thioamides, and sulfonamides. Polyfunctional amines and other polyfunctional compounds can also be prepared, and they enable significant extending of Mannich reaction. Similar oxygen compounds Bt-CRR′-OR″ enable new syntheses of ethers and esters. Reactions in which benzotriazole is eliminated rather than substituted open up new pathways to enamines, enol ethers, and nitrones. The methodology is capable of extension to a variety of vinylogous systems including benzenoid and heteroaromatic derivatives. In addition to acting as a versatile leaving group, benzotriazolyl residues activate neighboring CH bonds to proton loss and a variety of such applications is described.
- Katritzky, Alan R.,Rachwal, Stanislaw,Hitchings, Gregory J.
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p. 2683 - 2732
(2007/10/02)
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- Product Study of Some One-Electron Oxidations of Bibenzyl and 4-Ethylbibenzyl. Evidence against Carbon-Carbon Bond Cleavage of the Bibenzyl Radical Cation in Solution
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The oxidations of bibenzyl (1) and (or) 4-ethylbibenzyl (2) have been investigated under a variety of conditions, all of which should involve the intermediacy of bibenzyl radical cations: (a) reaction with ceric ammonium nitrate (CAN) in AcOH or CH3CN-H2O; (b) anodic oxidation in AcOH -CH3CN or (CH3)2CO-H2O; (c) photochemical oxidation by CAN in CH3CN; (d) photochemical autoxidation catalyzed by 9,10-dicyanoanthracene or by CAN in CH3CN.Nearly exclusive formation of side chain substituted products is observed for the chemical and electrochemical oxidations when the reactions are carried out in AcOH, CH3CN or AcOH-CH3CN, whereas extensive formation of C-C bond cleavage products occurs in the same processes when aqueous solvents are used.In the photochemical reactions, autoxidation produces both cleavage and side chain substituted products, whereas only the latter forms in the CAN-induced reaction in the absence of dioxygen.Evidence based on product analysis suggests that in these reactions no significant C-C bond breaking takes place at the state of bibenzyl radical cation.Cleavage products, where observed, nearly certainly derive from first-formed side chain substitution products
- Baciocchi, Enrico,Bartoli, Donatella,Rol, Cesare,Ruzziconi, Renzo,Sebastiani, Giovanni V.
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p. 3587 - 3593
(2007/10/02)
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- DENITROHYDROGENATION OF ALIPHATIC NITRO COMPOUNDS AND A NEW USE OF ALIPHATIC NITRO COMPOUNDS AS RADICAL PRECURSORS
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Aliphatic nitro groups are replaced by hydrogen on treatment with tributyltin hydride which proceeds via free radical chain processes.As the nitro group is selectively denitrated and other reducible groups are not affected with tributyltin hydride, this reaction can be used as a method for removing the nitro group from polyfunctional compounds.The radical intermediates generated via denitration can be also used for the carbon-carbon bond forming reactions.
- Ono, Noboru,Miyake, Hideyoshi,Kamimura, Akio,Hamamoto, Isami,Tamura, Rui,Kaji, Aritsune
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p. 4013 - 4024
(2007/10/02)
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- The Reactions of Cerium(IV) Ammonium Nitrate and Cobalt(III) Acetate with 1,2-Diphenylethanes in Acetic Acid. Evidence against the Involvement of Radical Cations in the Side-chain Oxidation of Alkylbenzenes by Co(OAc)3
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The oxidation of 1,2-diphenylethane and 2,3-dimethyl-2,3-diphenylbutane by cerium(IV) ammonium nitrate and Co(OAc)3 in acetic acid shows that a radical cation mechanism is plausible only in the reaction of the former oxidant.
- Baciocchi, Enrico,Ruzziconi, Renzo
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p. 445 - 446
(2007/10/02)
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