- N,N′-Dichlorobis(2,4,6-trichlorophenyl)urea (CC-2): An efficient reagent for conversion of oximes to ketones
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A method for the rapid conversion of oximes into the corresponding carbonyl compounds using N,N′-dichlorobis (2,4,6-trichlorophenyl)urea (CC-2) at room temperature is described. The method is economical as the solid by-product bis(2,4,6-trichlorophenyl)urea could be removed by filtration and recycled after re-chlorination.
- Gupta, Arvind K.,Acharya, Jyotiranjan,Pardasani, Deepak,Dubey, Devendra K.
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p. 411 - 414
(2008/02/12)
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- Investigations into the selective oxidation of vicinal diols to α-hydroxy ketones with the NaBrO3/NaHSO3 reagent: PH dependence, stoichiometry, substrates and origin of selectivity
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The NaBrO3/NaHSO3 reagent is one of the few oxidizing agents that chemoselectively oxidizes vicinal diols to α-hydroxy ketones with little overoxidation to the corresponding vicinal-dione or dicarboxylic acid. Oxidation reactions performed with this reagent showed strong pH dependence. cis-Vicinal diols reacted faster than trans-vicinal diols to the α-hydroxy ketone product. Hydroxy functional groups at axial ring positions were more readily oxidized than equatorial hydroxy groups. The application of the NaBrO3/NaHSO3 reagent for the chemoselective oxidation of vicinal diols was limited to simple systems and failed with more complex monosaccharide compounds probably due to acid catalyzed dehydrogenation reactions. Despite the simple reaction set-up and good selectivity towards the α-hydroxy ketone product, the actual oxidation reaction mechanism is highly complex and postulated to involve at least six different equilibria with a plethora of bromine containing species. A possible oxidation reaction mechanism is discussed.
- Bierenstiel, Matthias,D'Hondt, Paul J.,Schlaf, Marcel
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p. 4911 - 4917
(2007/10/03)
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- Ozonolyses of 1-alkyl-substituted 1-tert-butylethylenes and highly methylated methylenecycloalkanes. The influence of the substituent steric bulk on the direction of cleavage of the primary ozonides
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Ozonolyses of 1-alkyl-substituted 1-tert-butylethylenes and of highly methylated methylenecycloalkanes were conducted in the presence of trifluoroacetophenone (7) in ether. The ozonolysis of 2,2,6-trimethyl-1-methylenecyclohexane provided only the crossed-ozonide 10 derived from capture of formaldehyde O-oxide with the ketone 7 in 42% yield, while in the case of the relevant 2,2,5-trimethyl-1-methylenecyclopentane the alternative crossed-ozonide 15e derived from cycloaddition of 2,2,5-trimethylcyclopentanone O-oxide with the ketone 7 was the sole isolable product. The total energies of two possible cycloreversion processes for the primary ozonide 12c and for 12e, calculated at B3LYP/6-31G**//B3LYP/3-21G* level of theory, seem to reproduce the observed difference in the regiochemistry of fragmentation between these two primary ozonides.
- Kawamura, Shin-Ichi,Yamakoshi, Hideyuki,Abe, Manabu,Masuyama, Araki,Nojima, Masatomo
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p. 891 - 896
(2007/10/03)
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- Oxidation of α-Substituted Cyclohexanols by Nitric Acid
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The influence of α-substituents on the oxidative cleavage of cyclohexanol by nitric acid in the presence of copper(II) and vanadium(V) ions has been investigated.Following the initial oxidation to give the cyclohexanone, further reaction, leading to ring opening of the ketone, requires at least one α-hydrogen.Thus 2,2,6,6-tetramethylcyclohexanol is converted to the corresponding ketone whilst 2,2,6-trimethylcyclohexanol is oxidised to a mixture of dicarboxylic acids.The mechanisms of the oxidations are discussed and enolisation is shown to be the key to oxidative cleavage.For ketones that can give two alternative enols, reaction occurs predominantly via the more stable tautomer.
- Smith, John R. Lindsay,Thomas, C. Barry,Whittaker, Mark
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p. 2191 - 2194
(2007/10/02)
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- The chemistry of thujone. XVI. Versatile and efficient routes to safronitrile, β-cyclogeranonitrile, β-cyclocitral, damascones, and their analogues
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Thujone, a waste by-product of the Canadian forest industry, has been utilized as a starting material to develop a versatile synthetic route to the damascones (rose oil ketones) and related analogues.The synthetic sequence provides a route to β-cyclocitral (45), the latter having been previously converted to β-damascone (2).In addition, thujone-drived intermediates are converted to β-damascenone (48) and to intermediates that can be utilized for the preparation of damascone analogues.In conjunction with the above, an efficient route to safronitrile (42), β-cyclogeranonitrile (43), and β-cyclocitral (45) from 2,6-dimethylcyclohexanone has been developed.In summary, these studies afford an attractive versatile route to these important perfumery materials.
- Kutney, James P.,Gunning, Philip J.,Clewley, Robin G.,Somerville, John,Rettig, Steven J.
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p. 2094 - 2114
(2007/10/02)
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- ALKYLATION OF KETONES BY USE OF SOLID KOH IN DIMETHYLSULFOXIDE
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A mixture of solid KOH in dimethyl sulfoxide has a strong basicity, but only a low nucleophilicity and is used for α-methylation of ketones.With this simple and inexpensive reagent complete methylation with yields up to 90percent can be achieved.
- Langhals, Elke,Langhals, Heinz
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p. 859 - 862
(2007/10/02)
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- A Convenient Procedure for Complete Methylation of the α-Positions of Some Ketones
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2,2,6,6-Tetramethylcyclohexanone (2a), Pivalophenone (4a), and other complete methylated ketones can be prepared by a simple procedure.Therefore the ketone was treated with methyl iodide and powdered KOH in the presence of catalytical amounts of crown-6.
- Lissel, Manfred,Neumann, Beate,Schmidt, Stefan
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p. 263 - 264
(2007/10/02)
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- Steric and Stereoelectronic Effects in the Hydrogenolysis and Birch Reduction of Some Hindered Tertiary-Benzylic Carbinols
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3-(4'-Methoxyphenyl)pentan-3-ol (3a) and 3-(4'-methoxyphenyl)-2,4-dimethylpentan-3-ol (3b) underwent catalytic hydrogenolysis over 10percent palladium/charcoal at moderate temperatures and pressures.The more hindered tertiary-benzylic carbinols 3-(4'-methoxyphenyl)-2,2,4-trimethylpentan-3-ol (6), 3-(4'-methoxyphenyl)-2,2,4,4-tetramethylpentan-3-ol (3c), 1-(4'-methoxyphenyl)-2,2,6,6-tetramethylcyclohexan-1-ol (8) and 1-(1',1'-dimethylethyl)-6-methoxy-2,2-dimethyl-1,2,3,4-tetrahydronaphthalen-1-ol (10) were completely resistant to hydrogenolysis, even under vigorous conditions.While the hindered tertiary-benzylic carbinols (6), (8) and (10) readily underwent Birch reduction, the analogous di-t-butyl anisyl carbinol (3c) was unchanged.The failure of (3c) to undergo Birch reduction is probably due to a hitherto unrecognized stereoelectronic effect: the C-OH bond of (3c) is constrained to lie more or less in the plane of the benzene ring, and addition of an electron to the benzene ring of the derived oxyanion (31) is inhibited in this conformation.
- Collins, David J.,Jacobs, Howard A.
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p. 1989 - 2004
(2007/10/02)
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- ENANTIOSELECTIVE CARBOXYLATION OF A PROCHIRAL ENOLATE IN THE PRESENCE OF A CHIRAL LITHIUM AMIDE
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The prochiral lithium 2,2,6-trimethylcyclohexenolate (2) was prepared from ketone 1 by deprotonation with lithium (S,S)-α,α'-dimrthyldibenzylamide (4).Reaction of 2 with carbon dioxide at low temperature followed by methylation with methyl iodide yielded
- Hogeveen, H.,Menge, W. M. P. B.
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p. 2767 - 2770
(2007/10/02)
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- ALKYLATION DIRECTE DE CETONES ET D'ALDEHYDES EN PRESENCE DE POTASSE SOLIDE EN SUSPENSION
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Dehydrated solid KOH, suspended in aprotic solvents, is used as a base for ketone and aldehyde alkylation.The best solvent as regards yields and selectivity is DME.The quantity of KOH depends on the carbonyl compound acidity.This method gives as good results as less convenient homogeneous conditions.
- Artaud, I.,Torossian, G.,Viout, P.
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p. 5031 - 5038
(2007/10/02)
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- Oxidation of Thioketenes by Singlet Oxygen
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Oxidation of di-tert-butylthioketene (1) and 1,1,3,3-tetramethyl-2-(thiocarbonyl)cyclohexane (2) by singlet oxygen has been investigated and has been found to exhibit a unique behavior different from that of ketenes and ketenimines.Oxidation of 1 in methylene chloride yielded the corresponding thioketene S-oxide (3), thioketone S-oxide (4), and trans-2,2,7,7-tetramethyl-4-octene-3,6-dione (5), and that in methanol gave 3, 4, methyl 1-tert-butyl-3,3-dimethyl-2-oxobutanesulfinate (6), and 1-methoxy-3,3-dimethylbutanone (7).Similar oxidation of 2 in methylene chloride gave 1,1,3,3-tetramethyl-2-(thiocarbonyl)cyclohexane S-oxide (8), 2,2,6,6-tetramethylcyclohexanethione S-oxide (9), and 2,2,6,6-tetramethylcyclohexanone (10), and in methanol methyl 3,3,7,7-tetramethyl-2-oxocycloheptanesulfinate (11) and 10 were formed.Formation of the above products has been rationalized to arise through the involvement of zwitterionic intermediates (12) resulting from the attack of singlet oxygen on the sulfur lone pair of the thioketene functionality.The difference in behavior between 1 and 2 is suggested to be due to the difference in the nature of cleavage of the suspected intermediate α-peroxythiolactone.Reasons for the variation in the product distribution with respect to temperature and solvent are yet to be understood.
- Rao, V. Jayathirtha,Ramamurthy, V.,Schaumann, E.,Nimmesgern, H.
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p. 615 - 621
(2007/10/02)
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- Effets de cryptands et activation de bases. VI. Reactions d'organo-lithiens.
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Utilization of the cryptand shows the need of electrophilic catalysis by the Li(1+) ion in the nucleophilic addition of organolithium compounds to ketones, esters, or carboxylic acids.When nucleophilic addition is inhibited, organolithium reagents enolyze ketones or esters.When activated by cryptation of Li(1+), organolithium reagents attack ethers in a few minutes.With alkyl halides, only elimination takes place: exchange and nucleophilic substitution are not observed any longer in the presence of the cryptand.Generally speaking, the cryptand seems to enhance the basicity of the organolithium reagent, and nucleophilicity does not manifest itself any more.
- Perraud, Robert,Handel, Henri,Pierre, Jean-Louis
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p. 283 - 288
(2007/10/02)
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- C-NITROSO COMPOUNDS-XXXV REACTION OF ORGANOMETALLIC COMPOUNDS WITH 1-CHLORO-1-NITROSO-2,2,6,6-TETRAMETHYLCYCLOHEXANE
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Reaction of Grignard reagents and organolithium compounds (RM) with the congested 1-chloro-1-nitroso-2,2,6,6-tetramethylcyclohexane 1 leads to the formation of significant amounts of the reduction product 2,2,6,6-tetramethylcyclohexanone oxime 3 (61-90percent) together with the corresponding oxime O-R ether 4 (0-11percent).Attack on nitrogen is unimportant as shown by very low yields of nitrone.Formation of the products is rationalised with a pathway involving transfer of an electron from RM to 1.This leads-after separation of MCl-to a radical pair consisting of R. and the relatively stable iminoxy radical 2 (Schemes 1 and 2).Combination of these radicals explains formation of oxime ether 4 and nitrone 5, while reaction of iminoxy radical 2 with excess of RM can give oxime 3.Reactive radicals R. (i.e.Me,Ph, and to a minor extent n-Bu) are furthermore capable of abstracting hydrogen from the solvent (diethyl ether, toluene, or cumene), and the solvent derived radicals can also combine with 2 on oxygen, under formation of oxime ether (26percent of 6a).The corresponding benzyl- and cumyl ethers 6b and 6c are only formed in trace amounts because dimerisation of benzyl radicals (7percent) and cumyl radicals (22percent) is favoured.
- Schenk, C.,de Boer, Th. J.
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p. 1843 - 1846
(2007/10/02)
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- Gas-phase Thermolysis of a Thioketen-S-Oxide
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The unimolecular gas-phase thermolytic decomposition of 1,1,3,3-tetramethyl-2-thiocarbonylcyclohexane S-oxide (3) has been studied as a function of temperature by a flash vacuum thermolysis (f.v.t.) technique.The products detected are the carbenes (4) and (5), the ketone (6), the keten (7), the thioketone (8), and the thioketen (9).The product ratio is highly dependent on the thermolysis temperature.The thermolysis of (3) is mechanistically rationalized by assuming the existence of only two concurrent primary processes, which are (a) extrusion of atomic oxygen, leading to the thioketen (9), and (b) electrocyclic ring closure into the corresponding three-membered oxathiiran (10).The latter is dominant at lower temperatures, whereas higher thermolysis temperatures favour atomic oxygen extrusion.At further elevated temperatures additional concurrent primary reactions, i.e. extrusions of SO and CSO leading to the carbenes (5) and (4), respectively, are observed.Owing to an apparently very short half-life of the oxathiiran (10), only the decomposition products of the three-membered ring compound have been detected.These are the thioketone (8), formed by rearrangement of (10) into the α-thiololactone (11) followed by loss of CO, minor amounts of the ketone (6), formed analogously, and the keten (7), as a result of simple sulphur extrusion.
- Carlsen, Lars,Egsgaard, Helge,Schaumann, Ernst
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p. 1206 - 1211
(2007/10/02)
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