Symmetrical Ketones Research Articles

Asymmetric induction in Darzens condensation by means of (−)-8-phenylmenthyl and (−)-menthyl auxiliaries

Asymmetric Darzens condensation of benzaldehyde and various ketones has been investigated. The condensation of acetophenone, propiophenone and symmetric ketones with (–)-8-phenylmenthyl halogenoacetates 3a,b afforded the corresponding glycidic esters cis-12, cis-13 and 15–19 in 77–96% de, respectively, as the major products. Aza-Darzens condensation between N-benzylideneaniline and 3a occurred to give the trans-aziridine 21 as the major isomer in >85% de. The stereochemistry of the major diastereoisomers of cis-12 and 18 was confirmed by their conversion into the known optically active diols 22 and 24. The configuration of the major product of cis-12 was determined to be 2R,3R and that of 18 to be 2R. The geometric and disastereofacial selectivities were understandable in terms of the open-chain or non-chelated antiperiplanar transition state model in the initial aldol-type reaction.

Reactions of normal alcohols in the presence of a dehydrogenating iron catalyst

A oxidizing condensation of normal alcohols C4 to C12 in the gas phase over Fe3O4 catalyst containing Cr, Si and K oxides was studied. The reactions were carried out in a continuous process at atmospheric pressure. Initially the alcohols undergo dehydrogenation to aldehydes and esters, and at higher temperatures symmetric ketones containing 2n - 1 atoms of carbon in a molecule are formed. A mechanism for the reaction is proposed.

Carbonylative coupling of organozinc reagents in the presence and absence of aryl iodides: synthesis of unsymmetrical and symmetrical ketones

The utility of the palladium(0) catalysed reaction of the iodoalanine-derived organozinc reagent 6a with functionalised aryl iodides, under a carbon monoxide atmosphere, to give protected 4-aryl-4-oxo α-amino acids 8, is illustrated by a short synthesis of L-kynurenine 4. Treatment of functionalised organozinc reagents with catalytic tetrakis(triphenylphosphine)palladium(0) under an atmosphere of carbon monoxide in the absence of any electrophile leads to the formation of symmetrical functionalised ketones 9 in good yields. This reaction is illustrated by a one-step synthesis of protected (2S,6S)-4-oxo-2,6-diaminopimelic acid 9a from commercially available compounds. It has been established that adventitious molecular oxygen plays a key role in the formation of the symmetrical ketones 9, and that rigorous exclusion of oxygen can result in substantially higher yields of ketones 8 in the cross-coupling with some aromatic iodides.

Thermal analysis of long-chain ketones and the extrapolated equilibrium melting for polyethylene

Abstract The thermodynamic quantities of fusion for long-chain symmetrical ketone homologues were studied by DSC measurements. The carbon numbers in the chain measured were from 23 to 63. A heat-flux-type DSC was used because of its relatively high sensitivity at slow scanning rates. In addition to these, the heat capacities of ketones in the solid and liquid states were measured, for which sapphire was used as a standard material. Although the symmetrical ketones have almost the same crystal system and lattice constants as those of odd n-alkane crystals, known as model compounds for polyethylene, ketones have no high-temperature modifications. In view of these points, the purpose of this paper is to examine the linearity of the entropies of fusion, ΔSm(T0m) at the equilibrium melting temperature T0m for n = infinity, calculated using the DSC data measured with ketones, also considering the contributions of another entropy term, R ln n as pointed out by Flory and Vrij in 1963. It is concluded that not only the heats of fusions, ΔHm(T0m), but also ΔSm(T0m) satisfactorily indicate a linearity. Furthermore, it seems reasonable to conclude that the validity of the term R ln n is not clearly shown in these analyzed results.

A Mixed Aldol Condensation-Michael Addition Experiment

This article describes the anlysis of the recrystallized products of a mixed aldol condensation between symmetrical ketones and aromatic aldehydes.

A C2 Symmetric Chiral Ketone for Catalytic Asymmetric Epoxidation of Unfunctionalized Olefins

A <i>C</i>₂ Symmetric Chiral Ketone for Catalytic Asymmetric Epoxidation of Unfunctionalized Olefins

Synthesis of 1,3-diarylacetones from N-(arylacetyl)benzotriazoles via arylketene intermediates

Several 1-acylbenzotriazoles were synthesized and treated with sodium hydride to afford symmetrical ketones via the dimerization of intermediate ketenes followed by hydrolysis and the loss of carbon dioxide. © 1996 John Wiley & Sons, Inc.

Preparation of polyfunctional ketones by a cobalt(II) mediated carbonylation of organozinc reagents

Functionalized organozinc halides can be efficiently carbonylated under atmospheric pressure in the presence of cobalt(II) bromide in THF:NMP leading to polyfunctional symmetrical ketones in 56–80 % yield.

Pathway for the Catalytic Conversion of Carboxylic Acids to Hydrocarbons over Activated Alumina

Pure saturated carboxylic acids ranging from C 4 to C 12 were pyrolyzed at a WHSV of 0.46 h -1 over activated alumina at 450 °C and atmospheric pressure. The carboxylic acids produced symmetrical ketones that further degraded to methyl ketones and hydrocarbons presumably via a y-hydrogen transfer mechanism. The lower molar mass carboxylic acids yielded greater percentages of symmetrical ketones than the higher molar mass carboxylic acids. The organic liquid pyrolysate of butanoic acid (C 4 ) contained 78% 4-heptanone whereas the organic liquid pyrolysate of dodecanoic acid (C 12 ) contained negligible amounts of diundecyl ketone and greater percentages of hydrocarbons. Further pyrolysis of ketone-containing product yielded hydrocarbons. Similar compositions of the pyrolytic products from dodecanoic acid and diundecyl ketone revealed that virtually all of the carboxylic acid degraded to hydrocarbons via the symmetrical ketone. Monoenes were the major hydrocarbon products from ketones and were formed by γ-hydrogen transfer rearrangement, and/or reduction (disproportionation) to alcohol followed by dehydration. Methyl ketones had a distinct preference for reduction to monoenes (containing the same number of carbon atoms) following the latter route.

The acidity and tautomerism of β-diketones in aqueous solution

The acidity and keto–enol tautomerism of a series of symmetrical β-diketones (RCOCH2COR (1): R = methyl (a), phenyl (b), 3-pyridinyl (c), 4-pyridinyl (d), 3-(N-methyl)pyridinio (e), and 4-(N-methyl)pyridinio (f)) and two series of unsymmetrical β-diketones (RCOCH2COCH3(7a–7f) and RCOCH2COC6H5(8a–8f)) have been investigated in aqueous solution at 25 °C and ionic strength 0.1. Values of [Formula: see text] were measured spectrophotometrically, and the acidities of the enols [Formula: see text] were obtained from the analysis of the pH dependence of the buffer catalysis for the general acid-catalyzed protonation of the enolateconjugate bases. These data in turn allowed the calculation of the acidities of the keto tautomers [Formula: see text] and the equilibrium constants for enolization (KE = [Enol]/[Keto]). In general, KEis greater for the symmetrical ketones(1) than for the corresponding R-substituted unsymmetrical ketones (7 and 8). KEis much more sensitive to the nature of the R substituent in these three series of β-diketones than in the corresponding series of β-keto esters and amides. Correlations between [Formula: see text] for 8 and 7 combined with the known acidities of the corresponding β-keto esters and amides provide the first accurate estimates of the acidities of dimethyl malonate (pKa = 13.0)and malonamide (pKa = 12.5) in aqueous solution. Keywords: acidity, tautomerism, β-diketones.

ChemInform Abstract: Asymmetric Synthesis of Silanes with a Stereogenic Center at Silicon via Hydrosilylation of Symmetric Ketones with Prochiral Diaryl Silanes Catalyzed by BINAP‐Rh(I) Complexes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Facile syntheses of C2-symmetrical HIV-1 protease inhibitors.

With the goal of obtaining inexpensive yet potent anti-AIDS drugs, simple inhibitors of HIV-1 protease were synthesised. The C2-symmetrical pseudopeptidic substrate analogues can be prepared as inhibitors for HIV-1 protease starting from symmetrical ketones 3a-d by a facile four-step synthesis. After bromination of 3a-d to alpha,alpha'-dibromoketones 4a-d, we synthesised the diamino compounds 6a-c by Gabriel synthesis, which were then coupled with Z-valine to yield inhibitors including a central hydroxy group 8a-d a-i by azidation, reduction with LiAlH4 and coupling of the beta,beta'-diaminohydroxy compounds with appropriate peptides. The first set of compounds showed only weak inhibition whereas the latter reach Ki values of up to 3.0 microM.

Symmetry demand in polar excited state formation of 9,9′-bianthryl in clusters with some ketones

Laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectra have been studied for clusters of 9,9′-bianthryl (BA) with acetone, diethyl ketone, and methyl–ethyl ketone. Two different kinds of clusters have been observed in clusters containing the symmetric ketones. One shows broad LIF and DF spectra which are characteristic to the polar excited state of BA. The other shows sharp LIF bands and short lifetime which indicate the absence of the electron transfer.

Simultaneous determination of the heat capacity and the heat of the transitions for long-chain compounds with a heat-flux type DSC

The heat capacity method of DSC measurements, for which sapphire was used as a standard, was applied to determine simultaneously the heat of the transitions and the heat capacity for long-chain compounds. A heat-flux DSC was used because of its relatively high sensitivity at slow scanning rates. The data were analyzed with a computer system. Measurements on indium were performed to obtain information about factors affecting the accuracy. Fairly satisfactory results were obtained for the heat of melting and the heat capacity at heating rates of 0.5 and 2 K min −1. Long-chain symmetrical ketones were also used to test the reliability of the measurement because their thermal behavior is very simple. Solution-grown crystals of henpentacontane and dopentacontane clearly showed high-temperature modifications with a high heat capacity. Analysis by the present method indicates that the heat capacities of these modifications have a relatively large contribution to the overall change in enthalpy from the stable crystal at room temperature to the liquid.

The solubility limit of a solid solutions for the systems of long-chain symmetrical ketones in ann-alkane matrix

The systems of long-chain symmetrical ketones inn-alkane matrices form solid solutions for a low concentration range of the ketone, when the number of carbon atoms n in a ketone molecule Kn is equal to or lower than that in an-alkane molecule. The Kn examined were K25 to K39. The purity of all the samples used was very high. The solubility limit of these solid solutions was determined with DSC measurements. Above the solubility limit (the critical concentration) the systems changed to eutectic mixtures. The relationships for the solubility limit were derived, taking into consideration the lateral two-dimensional and the longitudinal positioning along the chain axes and the correlating energies. The multiplicity of the longitudinal positioning led to a remarkable increase in the solubility limit of the systems of Kn/Cn′ (n′>n). The present result points to the importance of the entropy of mixing and also for the stability of long-chain crystals.

Asymmetric synthesis of silanes with a stereogenic centre at silicon via hydrosilylation of symmetric ketones with prochiral diaryl silanes catalysed by binap–RhIcomplexes

Reaction of (1-naphthyl)phenylsilane with symmetric aliphatic ketones catalysed by (R)-Cybinap–RhI gave the corresponding (R)-(alkoxy)(1-naphthyl)phenylsilane in >99% enantiomeric excess.

Electrochemical synthesis of symmetrical ketones from acid chlorides

The electrochemical reduction of aroyl or arylacetyl chlorides was performed in an undivided cell fitted with a stainless steel anode and a nickel foam cathode. The electrolyses were carried out at constant current in acetonitrile as solvent, leading to the corresponding symmetrical ketones.

Cycloadditions, 43[1]. Cyclobutanones via Photoreactions of Chromium‐Carbene Complexes with Olefins and Dienes – A Comparison with the Traditional Ketene Method

AbstractPhotolysis of chromium‐carbene complexes 1 in the presence of olefins and dienes yields cyclobutanones 4 and 5 with varying stereoselectivity. Under oxidative conditions lactones 6, 7, 8, and 10 are obtained as byproducts. Thermal reactions of ketenes 3 with olefins and dienes yield the same cyclobutanones with usually equal selectivities. In the case of 2,3‐dihydro‐1,4‐dioxin as olefin, diene 9 is obtained as a byproduct. Cycloaddition reactions of 1a or 3a with 1,2‐dimethylenecyclopentane (11) yield the spirocyclic cyclobutanones 12 and 13. The symmetric ketone 16 and the ketene dimer 17 are formed as additional products upon cycloaddition of ketene 3b to tetraethoxyethylene. Novel α‐(butylthio)cyclobutanones 4j, k, l, m and 5k, l are formed by cycloaddition reactions of the newly prepared compounds 1c and 3c. The ketene dimer 20 is formed by thermal reactions of 3a with olefins. Unusually low stereoselectivities are observed in the case of photolytic reactions of 1c with dienes.

Diastereoselective ring-opening aldol-type reaction of 2,2-dialkoxycyclopropanecarboxylic esters with carbonyl compounds. 2. Synthesis of cis-2,3-substituted-γ-lactones

The reaction of 3-alkyl-2,2-dialkoxycyclopropanecarboxylic esters 1d–i with symmetrical ketones and formaldehyde was investigated. Cyclopropanes 1d–i react with symmetrical ketones and formaldehyde in the presence of TiCl 4 to give cis-2,3-substituted-γ-lactones in good yields with high diastereoselectivity. In the reaction of 3-ethylcyclopropane 1d, the reaction conditions hardly influenced the diastereoselectivity. Regarding the reaction of 3-methylcyclopropane 1f, however, the effect of the reaction conditions, especially the solvent, on the diastereoselectivity was observed. High chemoselectivity was also observed for the reaction of 1d with 1,4-cyclohexanedione mono-ethylene acetal ( 24). The isomerization of cis-γ-lactones by treatment with NaOEt in EtOH gives trans-isomers in good yields.

Enantioselective synthesis of 6-oxygenated atisine derivative via intramolecular double Michael reaction

An enantioselective synthesis of a 6-oxygenated atisine derivative 20 is described. The atisine skeleton 18 was stereoselectively constructed by the intramolecular double Michael reaction of the enone ester 16, derived, through the aldehyde 3, from the symmetrical ketone 4.