- Influence of phase transfer catalyst structure on the E : Z ratio in the O-alkylation of an enolate
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Both C- vs. O-alkylations and Z vs. E enol ether formation from 2-methyl-1,3-diphenylpropane-1,3-dione (1) can be influenced by the structure of the phase transfer catalyst. O-Methylation is the major process in the PTC reaction of 1 with dimethyl sulfate
- Dehmlow,Kaiser,Bollhoefer
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- Structural insights into the desymmetrization of bulky 1,2-dicarbonyls through enzymatic monoreduction
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Benzil reductases are dehydrogenases preferentially active on aromatic 1,2-diketones, but the reasons for this peculiar substrate recognition have not yet been clarified. The benzil reductase (KRED1-Pglu) from the non-conventional yeast Pichia glucozyma showed excellent activity and stereoselectivity in the monoreduction of space-demanding aromatic 1,2-dicarbonyls, making this enzyme attractive as biocatalyst in organic chemistry. Structural insights into the stereoselective monoreduction of 1,2-diketones catalyzed by KRED1-Pglu were investigated starting from its 1.77 ? resolution crystal structure, followed by QM and classical calculations; this study allowed for the identification and characterization of the KRED1-Pglu reactive site. Once identified the recognition elements involved in the stereoselective desymmetrization of bulky 1,2-dicarbonyls mediated by KRED1-Pglu, a mechanism was proposed together with an in silico prediction of substrates reactivity.
- Rabuffetti, Marco,Cannazza, Pietro,Contente, Martina Letizia,Pinto, Andrea,Romano, Diego,Hoyos, Pilar,Alcantara, Andres R.,Eberini, Ivano,Laurenzi, Tommaso,Gourlay, Louise,Di Pisa, Flavio,Molinari, Francesco
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supporting information
(2021/01/25)
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- Versatile CuI/Pd0 dual catalysis for the synthesis of quaternary α-allylated carbonyl compounds: Development, mechanistic investigations and scope
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We report herein a versatile cooperative dual catalysis reaction based on a CuI/Pd0 system. Mechanistic investigation shows that every component plays a crucial role in determining the reaction outcome. The reaction is successfully extended to various substrates; such as α,β-unsaturated ketones, malonates and coumarins. The strategy tolerates different substitution patterns and affords good yields for each family of substrates.
- Nahra, Fady,Mace, Yohan,Boreux, Arnaud,Billard, Francois,Riant, Olivier
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supporting information
p. 10970 - 10981
(2014/09/17)
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- Clemmensen reduction. XII The synthesis and acidolysis of some diaryl-substituted cyclopropane-1,2-diols. The possible involvement of a cyclopropyl cation
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The generation of a number of 1,2-diarylcyclopropane-1,2-diols is reported. Reaction of these in situ with acid gives, primarily, an α,β-unsaturated ketone in which the aryl substituent attached to the double bond is that which is best able to stabilize a benzylic cation. It is proposed that the reaction proceeds by O-protonation of the cyclopropane- 1,2-diol, followed by loss of water and opening of the resulting cyclopropyl cation and final deprotonation. Such initial O-protonation contrasts with the C-protonation normally observed in the acidolysis of cyclopropanols and other dialkyl- and alkylaryl-cyclopropane-1,2-diols.
- Davis, Brian R.,Hinds, Mark G.
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p. 309 - 319
(2007/10/03)
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- Additivity of the Electronic Meta-Substituent Effect in 3,5-Disubstituted Cumyl Radicals Assessed by the EPR D Parameter of 1,3-Arylcyclopentane-1,3-diyl Triplet Diradicals
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The D parameter (EPR zero-field splitting) of the 3,3′,5,5′-tetrasubstituted triplet diradicals 6 (X = X′ = H, NO2, CH3, OAc, OCH3, NH2, and OH) were determined in a MTHF matrix at 77 K and serves as a spectrosc
- Adam, Waldemar,Harrer, Heinrich M.,Maas, Wiebke
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p. 7263 - 7265
(2007/10/03)
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- Photochemistry of nonconjugated diketones: internal self-quenching and energy transfer
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The triplet state behavior of nine α,ο-dibenzoylalkanes indicates the occurrence of a rapid quenching interaction between the two carbonyl groups.This quenching is fastest (k=3E7 s-1) in dibenzoylbutane, is slightly slower (ca.E7 s-1) in dibenzoylethane, dibenzoylpentane, and 2,2-dibenzoylpropane, but is absent in 1,3-dibenzoylpropane.It also occurs in several "mixed" 1,4-diaroylbutanes incorporating p-ethylbenzoyl or p-methoxybenzoyl chromophores.This internal self-quenching is interpreted as the intramolecular counterpart of the well-know bimolecular self-quenching of aryl ketones, although no exact mechanism can be proposed.Such internal quenching does not occur as rapidly, if at all, in three "turned around" diketones: δ-(p-acetylphenyl)valerophenone, δ-(p-acetylphenoxy)valerophenone, and γ-(p-acetylphenoxy)butyrophenone.This fact, together with the varying rates of internal self-quenching in the dibenzoylalkanes, indicates the necessity for a very specific and close orientation of the two carbonyl groups for self-quenching.In the mixed diketones containing a p-alkylbenzoyl group, triplet excitation appears to be fully equilibrated between the two chromophores.However, in those containing a p-methoxybenzoyl group, excitation does not fully equilibrate before triplet decay, as evidenced by different quenching efficiencies for products from the two carbonyls.Analysis indicates intramolecular energy transfer rate constants -1.These are sufficiently lower than in other bichromophoric systems to suggest relatively slow energy hopping in the polymers of phenyl vinyl ketone.Key words: nonconjugated diketones, dibenzoylalkanes, sefl-quenching, energy transfer, triplet ketones.
- Wagner, Peter J.,Frerking, Harlan W. Jr.
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p. 2047 - 2061
(2007/10/03)
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- Diastereo- and regioselective synthesis of diquinanes and related systems from tricyclo[3.3.0.02,4]octanes by chemical electron transfer (CET)
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A new synthetic methodology for diquinanes by one-electron oxidation of tricyclo[3.3.0.02,4]octanes and subsequent stereocontrolled rearrangement is provided. The latter compounds are conveniently accessible through acid-catalyzed isopyrazole cycloaddition, followed by hydrogenation and photoextrusion of molecular nitrogen. The oxidative rearrangement of the tricyclooctanes proceeds catalytically and cleanly to afford regio- and diastereoselectively the corresponding diquinanes.
- Adam,Heidenfelder,Sahin
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p. 1163 - 1170
(2007/10/02)
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- Synthesis and Thermolysis of Ketal Derivatives of 3-Hydroxy-1,2-dioxolanes
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3--3,4,4,5-tetramethyl-5-phenyl-1,2-dioxolane (2), 3-methoxy-3,4,4,5-tetramethyl-5-phenyl-1,2-dioxolane (3), and 3-acetoxy-3,4,4,5-tetramethyl-5-phenyl-1,2-dioxolane (4) were synthesized from the corresponding 3-hydroxy-1,2-dioxolane (1a) under basic conditions. 3-Acetoxy-4,4-dimethyl-3,5,5-triphenyl-1,2-dioxolane (5) was also synthesized via this approach.Under acidic conditions, 3-hydroxy-1,2-dioxolane 1a underwent quantitative decomposition to phenol and 3,3-dimethyl-2,4-pentanedione.This competing degradation was dependent on the nature of the substituents at position-5.Methyl groups at position-5 slowed the degradative rearrangement whereas phenyl groups favored it. 3-Methoxy- and 3-(allyloxy)-4,4,5,5-tetramethyl-3-phenyl-1,2-dioxolanes (6, 7) were synthesized under acidic conditions from the appropriate 1,2-dioxolane precursors and the corresponding alcohols.At 60 deg C, derivatized 1,2-dioxolanes 2-7 were found to be more stable than the corresponding 3-hydroxy-1,2-dioxolanes.The first order rate constants for the thermolysis of 1,2-dioxolanes 2-7 were determined.Product studies showed that thermolysis of 2-5 yielded pairs of ketones and derivatized carboxylic acids.In addition to R-group migration products, an acetoxy migration product was observed for the thermolysis of 4.Thermolysis of 6 at 60 deg C in benzene yielded methyl benzoate and pinacolone, quantitatively.Thermolysis of 7 yielded products analogous to those for 6.No evidence for internal trapping of radicals by the carbon-carbon double bond of the allyloxy group in 7 was found.The thermolysis appeared to proceed with peroxy bond homolysis as the rate-determining step.Subsequent β-scissions of the intermediate 1,5-oxygen diradical with interesting rearrangements that show a high preference for alkyl vs phenyl migration account for the observed product distributions.The results suggest that the β-scission/rearrangement mechanism may not be concerted but rather stepwise to yield 1,3-diradical and carbonyl fragments.
- Baumstark, A. L.,Vasquez, P. C.,Chen, Y.-X.
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p. 6692 - 6696
(2007/10/02)
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- Electronic Substituent Effects on the Acid-Catalyzed + + 2> Cycloaddition of Isopyrazoles with Cyclopentadiene and the Photochemical and Thermal Denitrogenation of the Resulting 1,4-Diaryl-7,7-dimethyl-2,3-diazabicyclohept-2-ene Azoalk
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Eight symmetrically disubstituted 3,5-diaryl-4,4-dimethylisopyrazoles 6 with para and meta substituents (OMe, Me, H, F, Cl, Br, CN, NO2) and two unsymmetrically para-substituted derivatives (OMe and NO2; Me and CO2Me) were synthesized from the correspondi
- Adam, Waldemar,Harrer, Heinrich M.,Nau, Werner M.,Peters, Karl
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p. 3786 - 3797
(2007/10/02)
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- Photochemical Reaction of 3-Hydroxy-1-(o-methylaryl)alkan-1-ones: Formation of Cyclopropane-1,2-diols and Benzocyclobutenols through β- and γ-Hydrogen Abstractions
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Irradiation of 3-hydroxy-2,2-dimethyl-1-(o-methylaryl)-alkan-1-ones 1a-h having a bulky alkyl group or an aryl group on C-3 in methanol gave trans- and cis-cyclopropane-1,2-diols 2a-g and 3a, c-f, h and benzocyclobutenols 4a-h through β- and γ-hydrogen abstractions.Irradiation of 3-hydroxy-2,2-dimethyl-1-(o-methylphenyl)-alkan-1-ones 1i-k having ethyl, methyl or no substituent at C-3 gave benzocyclobutenols 4i-k and 1,3-diketones 5i, j, but no cyclopropane-1,2-diols.The cyclopropane-1,2-diols were sensitive to air and readily oxidized to the corresponding 1,3-diketones.Irradiation of 3-hydroxy-4,4-dimethyl-1-(o-methylaryl)pentan-1-ones 8a, b having a methyl group or no substituent on C-2 gave benzocyclobutenols 9a, b, the peroxide 10 and phthalides 11a, b. 3-Hydroxy-2,2-dimethyl-1,3-diphenylpropan-1-one 12a and 3-hydroxy-2,2,4-trimethylpentan-1-one 12b also underwent photocyclization through β-hydrogen abstraction to give cyclopropane-1,2-diols 13a, b and 14.
- Yoshioka, Michikazu,Miyazoe, Satoru,Hasegawa, Tadashi
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p. 2781 - 2786
(2007/10/02)
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- Synthesis of 4,4-Dimethyl-3,4-dihydro-3,3,5-trisubstituted-2H-pyrazoles and N-Benzoyl Derivatives: Method for "Hydrolysis" of Unreactive Amides and Carbamates
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Addition of organolithium reagents to 4,4-dimethyl-3,5-disubstituted-4H-pyrazoles produced a series of 4,4-dimethyl-3,4-dihydro-3,3,5-trisubstituted-2H-pyrazoles, 2-6, in good yield.The reaction was stereoselective: addition of organolithium compounds occurred only to carbon-3 of 4,4-dimethyl-3-alkyl-5-aryl-4H-pyrazoles.The 3,4-dihydro-2H-pyrazoles were found to be of high sensitivity to oxygen.For long term storage and ease of handling, N-benzoyl derivatives were synthesized.Removal of protecting group could not be accomplished by use of many standard sets of conditions.Deprotection was accomplished in high yield by reaction of the N-benzoyl-4,4-dimethyl-3,4-dihydro-3,3,5-trisubstituted-2H-pyrazoles with anhydrous potassium t-butoxide in toluene in the presence of a phase transfer catalyst (18-Crown-6).Cleavage of a N-carbamate derivative was also achieved by this phase transfer approach.This methodology should be applicable to the hydrolysis of unreactive amides and carbamates in general.
- Baumstark, Alfons L.,Choudhary, Anil,Vasquez, Pedro C.,Dotrong, My
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p. 291 - 294
(2007/10/02)
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- Convenient, High-Yield Method for the Methylation of 1,3-Diketones
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A general method for the facile dimethylation of 1,3-diketones is presented.The method involves the use of readily available, inexpensive reagents and is carried out under mild conditions.Monomethylation may be carried out by slight modification (simplification) of the procedure.Several examples are presented which show that the method is applicable to alkylations with primary halides as well.Isolated yields for monoalkylation are approximately 95percent while those for dialkylation are ca. 90percent.Alkylation is taking place by the reaction of the enolates of 1,3-diketones with alkyl halides.
- Choudhary, Anil,Baumstark, Alfons L.
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p. 688 - 690
(2007/10/02)
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- ACYLATION OF α-BROMINATED KETONES IN THE PRESENCE OF ZINC
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The acylation of α-bromo ketones in the presence of zinc takes place preferentially at the O-reaction center of the intermediate organozinc compound.
- Fotin, V. V.,Shchepin, V. V.,Sinani, S. V.
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p. 1744 - 1746
(2007/10/02)
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- THE REACTIONS OF N-BENZOYLPEROXYCARBAMIC ACID WITH AZINES AND IMINES
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N-Benzoylperoxycarbamic acid (BPC) was found to react generally with imines and azines to form oxaziridines rather than N-oxides.The imine products were stable, but those found from azines apparently were unstable and converted to ketones or aldehydes plus diazo compounds.
- Paredes, Rodrigo,Bastos, Holger,Montoya, Raul,Chavez, Alba Lucia,Dolbier, William R.,Burkholder, Conrad R.
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p. 6821 - 6830
(2007/10/02)
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- Azo Bridges from Azines, VI. - Substituted Isopyrazoles as Electron-deficient Dienes for the Synthesis of 2,3-Diazabicycloheptenes and their Photochemistry
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The ++2> cycloaddition of isopyrazoles (4H-pyrazoles) 3c-e and cyclopentadiene, norbornene, and norbornadiene leads to the azo-bridged products 5, 8, 11, and 12c-e.Irradiation of 5e, 8e, and 11e expectedly produces the tricycles 13, 15, and 17 by loss of nitrogen.In contrast, as a result of the parallel arrangement of the C=C/N=N bonds, the isomers 12c-e are transformed nearly quantitatively into diazetidines 14, 16, and 18; despite the pronounced photolability of the diazabicycloheptene moiety in 12, cycloaddition is preferred over nitrogen elimination.
- Beck, Karin,Huenig, Siegfried
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p. 477 - 484
(2007/10/02)
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- Oxidative cyclization of some 1,3-Dioximes with Lead Tetraacetate
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Oxidation of 1,3-dioximes 1 with lead tetraacetate gives di-N-oxides of pyrazolines 4 or pyrazoles 5 or N-oxides of oxadiazines 7 as the main reaction products.The reaction mechanism is discussed.
- Stephanidou-Stephanatou, J.
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p. 293 - 295
(2007/10/02)
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- Stereoselectivity in the Hydride Reduction of Acyclic Diketones (1,2-, 1,3-, 1,4-, and 1,5-Induction)
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Diketones 2, 5, 9, and 19 as well as hemiketal 22 react with lithium aluminum hydride to give mixtures of d,l- and meso-diols.The stereochemical assignment of the diols can be obtained either by direct comparison with authentic samples (1,2-diols) or by NMR differentiation of diastereotopic groups (1,3- and 1,5-diols) or by stereospecific cyclization to the sila-heterocycles 12 and 13 (1,4-diols).The 1,2- and 1,4-diketones preferably produce meso-diols, whereas 1,3- and 1,5-diketones mostly lead to d,l-isomers.These alternating stereoselectivities can be explained by a stepwise reduction generating complexes of types 24 - 27 which are attacked by excess hydride via a diastereoface differentiating mode.
- Maier, Guenther,Roth, Cornelia,Schmitt, Reinhart K.
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p. 704 - 721
(2007/10/02)
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- The Beckmann Reaction of Phenyl-substituted 1,3-Dioximes
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The 1,3-diketones 1a - c react with hydroxylammonium choride to give isoxazolin-5-ols 2a - c predominantly, in addition to dioximes 3a and b, respectively.The anti (E,E) configuration of the dioximes was established by UV and 1H NMR.By Beckmann reaction of 3a, b and d, 4H-pyrazole N-oxides 4a, b and d were formed.The amphi (Z,E) configuration of 1,3-bis(hydroxyimino)-1,3-diphenyl-2-propanone (6) was established by 13C NMR.
- Gnichtel, Horst,Boehringer, Ulrich
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p. 1507 - 1513
(2007/10/02)
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