- Photocatalytic carbanion generation from C-H bonds-reductant free Barbier/Grignard-type reactions
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We report a redox-neutral method for the generation of carbanions from benzylic C-H bonds in a photocatalytic Grignard-type reaction. The combination of photo- and hydrogen atom transfer (HAT) catalysis enables the abstraction of a benzylic hydrogen atom, generating a radical intermediate. This radical is reduced in situ by the organic photocatalyst to a carbanion, which is able to react with electrophiles such as aldehydes or ketones, yielding homobenzylic secondary and tertiary alcohols.
- Berger, Anna Lucia,Donabauer, Karsten,K?nig, Burkhard
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p. 10991 - 10996
(2019/12/28)
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- DTBB-Catalysed dilithiation of styrene and its methyl-derivatives: Introduction of two electrophilic reagents
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The reaction of styrene and some methyl-substituted styrenes 1 with lithium and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB) in the presence of several electrophiles [Me3SiCl, Me2CO, Et2CO, (CH2)5CO, Pr2CO], in THF, at temperatures ranging from -78 to 0°C, gave, after hydrolysis, products 2 resulting from addition of lithium to the olefinic double bond and successive trapping with the electrophilic reagent. When a carbonyl compound was used as electrophile, mixtures of the monoaddition-reduction compounds 3 and 4 were obtained as by-products, which could be easily separated from the diaddition products 2.
- Yus, Miguel,Martínez, Pedro,Guijarro, David
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p. 10119 - 10124
(2007/10/03)
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- Generation of allylic and benzylic organolithium reagents from the corresponding ester, amide, carbonate, carbamate and urea derivatives
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The reaction of different allylic and benzylic non-enolisable esters or amides (1), carbonates (4), carbamates (6, 7) and ureas (8) with an excess of lithium powder and a catalytic amount of naphthalene (10%) in the presence of an electrophile [(i)PrCHO, (t)BuCHO, PhCHO, Me2CO, Et2CO, (CH2)5CO, Ph2CO, Me3SiCl] in THF at different temperatures (-78, -30 or 0°C) leads, after hydrolysis with water to the corresponding allylated or benzylated products (2).
- Alonso, Emma,Guijarro, David,Martinez, Pedro,Ramon, Diego J.,Yus, Miguel
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p. 11027 - 11038
(2007/10/03)
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- Reactivity and Selectivity in the Oxidation of Styrene Derivatives. IV. Studies on the Oxidation of Substituted β,β-Dimethylstyrenes
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The liquid phase oxidation of substituted (p-MeO-, p-Cl-, m-CF3-) 2-aryl-3-methyl-but-2-enes, of 1,1-diphenyl-2-methyl-propene, of 1-ethoxy-2-methyl-1-phenyl-propene and of 9-isopropylidene-fluorene with pure oxygen was investigated in chlorobenzene solution and in presence of cumene and of cumene hydroperoxide in the temperature range 65-125°C. The product yields were determined gaschromatographically. The differences of the activation energies of epoxide formation and the parallel reactions were calculated. They amount to 19-48 kJ/mol. The epoxide selectivity increases with increasing temperature and increasing concentration of olefin. The relative chain propagation constants (kpC=C) were determined by competitive oxidation with cumene. The kpC=C values of substituted β,β-dimethylstyrenes can be correlated by a LFE-relationship with the ionisation energies of the olefins.
- Suprun
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p. 247 - 255
(2007/10/03)
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- Reductive opening of 2-phenyl-1,3-dioxolanes by a naphthalene-catalysed lithiation: Synthetic applications
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The reaction of 2-phenyl-1,3-dioxolanes 1a,b with an excess of lithium powder in the presence of a catalytic amount of naphthalene (4 mol %) in tetrahydrofuran at -40°C followed by successive reaction with an electrophile and final hydrolysis with water at the same temperature yields the corresponding monoprotected 1,2-diols 2aa-2bf. The same process but allowing to rise the temperature to 20°C before the hydrolysis affords alcohols 3aa-3bd. The use of 2,2-diphenyl-1,3-dioxolane 1d, under similar reaction conditions as for compounds 2, permits the isolation of 2,2-diphenylalcohols 11da-11dc, resulting from the reaction with two different electrophiles. A mechanistic rationalization for all processes is given.
- Gil, Juan F.,Ramon, Diego J.,Yus, Miguel
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p. 9535 - 9546
(2007/10/02)
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- REACTIONS OF OXIRANES WITH ALKALI METALS: INTERMEDIACY OF RADICAL-ANIONS
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Reaction of oxiranes with alkali metals in aprotic solvents yields a variety of products depending on the nature of the metal and the structure of the oxirane.Deoxygenation to olefins is the major reaction in case of lithium.Rearrangement to carbonyl compounds, reduction to alcohols and formation of dimeric products occur when oxiranes are treated with sodium.All the reactions could be rationalised by a mechanism involving an initial single electron transfer leading to the formation of radical-anion intermediate.
- Gurudutt, K. N.,Pasha, M. A.,Ravindranath, B.,Srinivas, P.
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p. 1629 - 1632
(2007/10/02)
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- Photochemistry of Phenyloxiranes in Neutral Media: Reactions of Some Styrene Epoxides
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The epoxides 1 and 2 on photoirradiation in alcohols (MeOH, EtOH, PriOH) containing Na2CO3 undergo cleavage of the C-O bond exclusively to give the respective phenylacetaldehydes which provide benzyl radicals on rapid photodecarbonylation.These radicals readily combine with ketyl radicals derived from alcohols to give phenyl substituted alcohols.However, a similar irradiation of the epoxide 3 affords products involving the scission of both C-O and C-C bonds.A suitable mechanism has been proposed to explain the formation of these products.
- Sonawane, H. R.,Sethi, S. C.,Merchant, S. N.
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p. 940 - 943
(2007/10/02)
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- PHOTOSUBSTITUTION OF BENZYL HYDROGENS WITH ALCOHOLIC MOIETIES. SELECTIVE FORMATION OF ALKYLBENZENE CARBINOLS
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Irradiations of alkylbenzene compounds with various alcohols in an air atmosphere, resulted in substitution of the benzyl hydrogens with alcoholic moieties in a very selective mode.
- Pasternak, Mordechai,Morduchowitz, Abraham
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p. 3439 - 3442
(2007/10/02)
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- PHOTOCHEMICAL OXIDATION AND DIMERIZATION OF ALKYLBENZENES. SELECTIVE REACTIONS OF THE ALKYL SIDE GROUPS
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Irradiations of alkylbenzene compounds in an oxygen atmosphere result exclusively in oxidation reactions, while in a less oxidative environment dimerization processes predominate.Under all conditions studied, the reactions took place only at one benzyl position.
- Pasternak, Mordechai,Morduchowitz, Abraham
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p. 4275 - 4278
(2007/10/02)
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- ELECTROCHEMICAL ADDITIONS OF THE ALLYL AND THE BENZYL GROUPS OF ALLYL AND BENZYL HALIDES TO ACETONE.
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Electrolysis of allyl chloride and five molar excess of acetone in hexamethylphosphoric triamide containing 0. 5 M tetrabutylammonium perchlorate gave an addition product, 2-methyl-4-penten-2-ol, in a 53% yield. Allyl groups of 1-chloro-2-methyl-2-propene, 1-chloro-2-butene(3), 3-chloro-1-butene(4), 1-chloro-3-methyl-2-butene(5), and 3-chloro-3-methyl-1-butene(6), and benzyl groups of benzyl chloride, benzyl bromide, and 1-chloro-1-phenylethane can similarly be added to acetone by electrolysis to give the corresponding alcohols in fair to good yields. Among these electrochemical reactions, those of 3, 4, 5 and 6 with acetone give respectively two isomeric homoallyl alcohols, one of the isomers is not accessible by the usual chemical reaction between allylic organometallics and acetone.
- Satoh,Suginome,Tokuda
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p. 1791 - 1794
(2007/10/02)
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