- Hydrotalcite-catalyzed alkylation of 2,4-pentanedione
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A synthetic anionic clay, hydrotalcite (Mg/Al = 2.8), calcined under dry air at 450°C has proved to be an efficient catalyst for the selective C-monoalkylation of 2,4-pentanedione with reactive alylating reagents.
- Cativiela,Figueras,Garcia,Mayoral,Zurbano
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- Extended reaction scope of thiamine diphosphate dependent cyclohexane-1,2-dione hydrolase: From C-C bond cleavage to C-C bond ligation
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ThDP-dependent cyclohexane-1,2-dione hydrolase (CDH) catalyzes the CC bond cleavage of cyclohexane-1,2-dione to 6-oxohexanoate, and the asymmetric benzoin condensation between benzaldehyde and pyruvate. One of the two reactivities of CDH was selectively knocked down by mutation experiments. CDH-H28A is much less able to catalyze the CC bond formation, while the ability for CC bond cleavage is still intact. The double variant CDH-H28A/N484A shows the opposite behavior and catalyzes the addition of pyruvate to cyclohexane-1,2-dione, resulting in the formation of a tertiary alcohol. Several acyloins of tertiary alcohols are formed with 54-94% enantiomeric excess. In addition to pyruvate, methyl pyruvate and butane-2,3-dione are alternative donor substrates for CC bond formation. Thus, the very rare aldehyde-ketone cross-benzoin reaction has been solved by design of an enzyme variant.
- Loschonsky, Sabrina,Wacker, Tobias,Waltzer, Simon,Giovannini, Pier Paolo,McLeish, Michael J.,Andrade, Susana L. A.,Müller, Michael
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supporting information
p. 14402 - 14406
(2015/02/19)
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- Novel C2-symmetric chiral O,N,N,O-tetradentate 2,2-bipyridyldiolpropane ligands: Synthesis and application in asymmetric diethylzinc addition to aldehydes
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First synthesis of C2-symmetric chiral O,N,N,O-tetradentate 2,2-bipyridyldiolpropane ligands is described. The Mukaiyama-Michael reaction was applied as an important reaction for the synthesis of 2,2-bipyridylpropane 9. Among the ligands synthesized, ligand 11 exhibits excellent chiral induction (up to 97% ee) in diethylzinc addition to various aldehydes. The use of additional Lewis acid such as Ti(OiPr)4 in diethylzinc addition reaction is not required for the present catalytic system.
- Shih, Yi-Shan,Boobalan, Ramalingam,Chen, Chinpiao,Lee, Gene-Hsian
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p. 327 - 333
(2014/04/03)
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- Synthesis and biological evaluation of new curcumin derivatives as antioxidant and antitumor agents
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Twenty-four new compounds were prepared, taking curcumin as a lead, in order to explore their antioxidant and antitumor properties. The capacities of these derivatives to scavenge the 2,2′-azinobis(3-ethylbenzothiazoline-6- sulfonic acid) radical cation (ABTS.+), and to protect human red blood cells (RBCs) from oxidative haemolysis were investigated. In addition, the percentage viability of different cell lines (Hep G2, WI38, VERO and MCF-7) was tested. The result of the antitumor testing was generally in accordance with those of the antioxidant assays. Compounds which bear o-methoxy substitution to the 4-hydroxy function in the phenyl ring (7g, 5g and 3g) exhibited significantly higher ABTS.+-scavenging, antihaemolysis, and antitumor activities than other derivatives. In addition, molecular modelling studies were carried out for biologically active and inactive compounds, to study the structure-activity relationship, with the aim to elucidate which portions of the molecules are critical for the antioxidant and antitumor activity.
- Bayomi, Said M.,El-Kashef, Hassan A.,El-Ashmawy, Mahmoud B.,Nasr, Magda N. A.,El-Sherbeny, Magda A.,Badria, Farid A.,Abou-Zeid, Laila A.,Ghaly, Mariam A.,Abdel-Aziz, Naglaa I.
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p. 1147 - 1162
(2013/04/10)
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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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- Surface-mediated Solid-phase Reaction. Part 2. Highly Selective Mono- and Di-C-alkylation of 1,3-Dicarbonyl Compounds on the Surface of Alumina
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Highly selective mono- and di-C-alkylation of 1,3-dicarbonyl compounds with different, structurally varied alkyl halides has been achieved in high yields through a simple solvent-free reaction on the surface of alumina impregnated with sodium or potassium alkoxide.
- Ranu, Brindaban C.,Bhar, Sanjay
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p. 365 - 368
(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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- 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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- 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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- Chemistry of 1,3-Glycol Derivatives. IV. Mechanism of the Solvolyses of 2,4-Pentanediol Derivatives and the Reactions of the Proposed Intermediate Acetoxonium Ions with Carbanions and Hydride
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Regio- and stereochemical studies of the solvolyses of various kinds of 2,4-pentanediol derivatives, including 2-acetoxy-4-tosylates, cyclic orthoformates and orthoacetates, have been done and the previously proposed mechanism has been partially revised. The reactions of the proposed intermediate acetoxonium ions with carbanions and with a hydride ion have also been studied.
- Itoh, Osamu,Iwakoshi, Naoki,Saitoh, Toshihide,Katano, Hiroaki,Fujisawa, Yoshiki,et al.
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p. 177 - 181
(2007/10/02)
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- Reactions of Mercury(II) Acetate with Nitrogen Compounds. Part 9. Oxidations of the Bis-(4-nitrophenylhydrazone)s of Some 1,3-Diketones with Mercury(II) Acetate and Lead(IV) Acetate
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Oxidation of bis-(4-nitrophenylhydrazone)s of 1,3-diketones containing an α-CH between the hydrazone chains resulted in cyclization with fragmentation, giving pyrazoles.The reaction is considered to involve dehydrogenation of the conjugated tautomeric enamine form of the bis-hydrazone, giving a cis-azo-hydrazono-alkene intermediate.When the postulated azo-hydrazono-alkene intermediate had trans-stereochemistry, unfavourable for cyclization, as in the oxidation of cycylohexa-1,3-dione bis-(4-nitrophenylhydrazone), the azo-alkene was stable and was the main product.When the conjugated enamine tautomeric form of the 1,3-bis-hydrazone cold not exist, as with 3,3-dimethylpentane-2,4-dione bis-(4-nitrophenylhydrazone), pyrazoles were not formed and the hydrazone chains behaved as isolated monohydrazones.
- Butler, Richard N.,James, John P.
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p. 553 - 555
(2007/10/02)
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- Hydrogenolysis of Small Cycloalkanes, VII. Selective Hydrogenation of 1,1-Disubstituted Cyclopropane Derivatives
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On hydrogenation of 1,1-disubstituted cyclopropane derivatives 1 hydrogenolysis of the C-2-C-3 bond to yield 2 is promoted by electron releasing groups (R =alkyl, CH2OH, OR).On the other hand the presence of electron attracting substituents (R = CO2R, COR, CN) causes opening of the C-1-C-2 bond and formation of products 3. 1,1-Bis(trifluoromethyl)cyclopropane could not be hydrogenated.
- Groeger, Claus,Musso, Hans,Rossnagel, Ingrid
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p. 3621 - 3628
(2007/10/02)
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