Showing papers in "Arkivoc in 2002"
TL;DR: In this paper, the tautomerism of substituted 2-hydroxypyridines is investigated by UV/Vis- and 1 H-, and 13 C- NMR spectroscopic methods, with the aid of the N-Me and O-Me fixed parents.
Abstract: The tautomerism of some substituted 2-hydroxypyridines is investigated by UV/Vis- and 1 H-, and 13 C- NMR spectroscopic methods, with the aid of the N-Me and O-Me fixed parents. NMR spectroscopic data do not allow discrimination between the two tautomeric forms (with the exception of the unsubstituted 2-hydroxypyridine), while UV/Vis- data permit the quantitative determination, in different solvents, of the amounts of the two forms. The electronic substituent effect and the change of solvent are discussed. An X-Ray diffraction study carried out on a crystal of 2-hydroxy-5-nitropyridine (7) reveals that this compound, in the solid state, is in the oxo-form.
59 citations
TL;DR: In this paper, a review summarizes the tremendous achievements in the field of catalytic enantioselective Michael addition reaction involving the attack of soft nucleophiles on α,β- unsaturated systems.
Abstract: This review summarizes the tremendous achievements in the field of catalytic enantioselective Michael addition reaction involving the attack of soft nucleophiles on α,β- unsaturated systems. The reaction has evolved during past two decades, from stoichiometric to catalytic. A large number of efficient catalytic systems have been used to generate chiral Michael adducts in high optical purity. Several chiral alkaloids were used for the enantioselective addition of thiols and dialkylmalonates to cyclic and linear enones to give product in moderate to high enantioselectivity. Chiral crown ethers in conjugation with metal alkoxides were found to be the catalyst of choice for the addition of substituted α-phenylesters to linear enones. Proline derived catalysts gave product in moderate in moderate to high enantioselectivity where NO2 group was present as an activator in either Michael donor or acceptor. BINAP based catalysts were found to be superior in Michael addition of α-nitrile substituted esters to linear enones. A new class of heterobimetallic catalysts based on BINOL ligand was found to be highly versatile for an array of Michael donors and acceptors to provide products in very high optical purity. Metal complexes based on chiral N,N-dioxides were found to be superior for the addition of arylthiols to both linear and cyclic enones to have product in high enantiomeric excess.
43 citations
TL;DR: A variety of amines undergo Michael-type additions to α, β-unsaturated nitriles, carboxylic ester and ketones in a neat mixture without any solvent and catalyst to produce the corresponding β- amino derivatives in excellent yields as mentioned in this paper.
Abstract: A variety of amines undergo Michael-type additions to α,β-unsaturated nitriles, carboxylic ester and ketones in a neat mixture without any solvent and catalyst to produce the corresponding β- amino derivatives in excellent yields.
41 citations
TL;DR: In this article, the effects of ultrasound on mass transport, upon electrode surface phenomena, upon the behaviour of species and upon reaction mechanisms, and selected examples of the benefits of insonation in electroanalysis, electrosynthesis, electrodeposition and electrochemiluminescence are discussed.
Abstract: This paper comprises the text of a review lecture on the subject of the effects of ultrasound upon mass transport, upon electrode surface phenomena, upon the behaviour of species and upon reaction mechanisms, and selected examples of the benefits of insonation in electroanalysis, electrosynthesis, electrodeposition and electrochemiluminescence are discussed.
40 citations
TL;DR: A variety of amines react with Boc2O in the presence of a catalytic amount of yttria-zirconia based catalyst to afford the corresponding N-Boc products in excellent yields.
Abstract: A variety of amines react with Boc2O in the presence of a catalytic amount of yttria-zirconia based catalyst to afford the corresponding N-Boc products in excellent yields.
39 citations
TL;DR: The chiral α-N-(tert-butoxycarbonyl)aminoacylbenzotriazoles ((N-Boc-amino-acyl)-benzotsarazoles) 3a−e are stable crystalline intermediates, easily prepared (61-88%) from N −Boc α-α amino acids.
Abstract: The chiral α-N-(tert-butoxycarbonyl)aminoacylbenzotriazoles ((N-Boc-aminoacyl)-benzotriazoles) 3a−e are stable crystalline intermediates, easily prepared (61-88%) from N-Boc-α-amino acids 1a−e. Compounds 3a−e react with achiral or chiral amines at 0-20 o C to give α-(N-Boc-amino)amides with no detectable racemization.
35 citations
TL;DR: In this article, an efficient conversion of carboxylic acids into Weinreb amides was achieved by treatment of N- acylbenzotriazoles 2a-i with N,O-dimethylhydroxylamine hydrochloride under mild conditions.
Abstract: Efficient conversions of carboxylic acids into Weinreb amides were achieved by treatment of N- acylbenzotriazoles 2a-i with N,O-dimethylhydroxylamine hydrochloride under mild conditions No racemization was found when optically active acids were employed
32 citations
TL;DR: In this paper, the synthesis and fluorescence properties of stable nitroxide free radicals (10a, 11a, 12a, 14a, 20a, 21a) and their amine precursors covalently linked to dansyl or 3-and 4-aminophthalimide are reported.
Abstract: Synthesis and fluorescence properties of stable nitroxide free radicals (10a, 11a, 12a, 14a, 20a, 21a) and their amine (10b, 11b, 12b, 14b, 20b, 21b) precursors covalently linked to dansyl or 3- and 4-aminophthalimide are reported. The best intramolecular quenching is achieved when the fluorophore and the nitroxide are in the closest possible position
30 citations
TL;DR: The sydnones 7a,b and 8a-c gave the corresponding pyrazoles 9a-e by 1,3-dipolar cycloaddition with dimethyl acetylenedicarboxylate (DMAD) as mentioned in this paper.
Abstract: The sydnones 7a,b and 8a-c gave the corresponding pyrazoles 9a-e by 1,3-dipolar cycloaddition with dimethyl acetylenedicarboxylate (DMAD). The highly sterically hindered 3-(4,6-dibromo- 2-methylphenyl)-4-iodosydnone (8d) failed to react with DMAD on heating in boiling xylene. The iodination of sterically hindered sydnone 7b required more drastic reaction conditions than the sydnone 7a.
27 citations
TL;DR: Di(benzotriazolyl)methanimine 1 was used for convenient preparation of previously unknown triazoles 11a,b and 15a-d and as a new reagent for the synthesis of oxadiazoles 17a-j as discussed by the authors.
Abstract: Di(benzotriazolyl)methanimine 1 was used for convenient preparation of previously unknown triazoles 11a,b and 15a-d and as a new reagent for the synthesis of oxadiazoles 17a-j.
23 citations
TL;DR: In this article, the preparation of chiral heterocyclic compounds of the thiadiazoline types, starting from natural terpenones such as fenchone, camphor and menthone, is described.
Abstract: Preparation of chiral heterocyclic compounds of the thiadiazoline types, starting from natural terpenones such as fenchone, camphor and menthone, is described. Stereochemical assignment of the compounds synthesized was performed by NMR spectroscopy and X-ray analysis.
TL;DR: In this paper, principal properties for solvents were extended to 113 solvent classes by the addition of ten ethers, suitable for solvent optimization in Grignard reactions, and their physico-chemical significance was discussed.
Abstract: Principal properties (PPs) for solvents were extended to 113 solvents by the addition of ten ethers. Specific "PPs" for ethers, suitable for solvent optimization in Grignard reactions, were also derived and their physico-chemical significance discussed.
TL;DR: In this article, the authors used CODESSA, GFA and CROMRsel methods for descriptor selection for predicting viscosities at 20 °C, and obtained a very good nonlinear MR model having five descriptors.
Abstract: Improved models for predicting viscosities at 20 °C were generated using three different methods for descriptor selection. Data set of 361 diverse organic molecules and their experimental viscosities were used for developing the models. Molecular properties are encoded by 822 initial descriptors computed by the CODESSA program. CODESSA, GFA and CROMRsel methods are capable of selecting good and facile viscosity models having only five descriptors. These methods are automated procedures for generation of simple multiregression (MR) models. All three methods produce excellent linear models, but the models obtained by the CROMRsel method are somewhat better. In addition, using the CROMRsel suite of programs a very good nonlinear MR model having five descriptors (two linear and three cross-product descriptors, R 2 = 0.908, S = 0.175) was obtained. Nonlinear models generated in this study show that the classical MR based methods can be efficiently used to obtain simple and very good nonlinear MR models. The best five-descriptor models selected in this study usually contain one geometrical (gravitational index) and one topological descriptor (Randic index of order 0), and three electrostatic descriptors which reflect the bonding properties of molecules, i.e. their capabilities to create (mainly) hydrogen bonds. Because of that, hydrogen-donors and hydrogen-acceptors surface areas, charges, total molecular surface areas, and maximum net atomic charges and state energies for oxygen atoms appear to be key factors for modeling the viscosity of organic molecules.
TL;DR: The exoskeleton lipids of three dangerous pests, Sitobion avenae, Hyalopterus pruni and Brevicoryne brassicae were identified by GC/MS studies.
Abstract: The exoskeleton lipids of three dangerous pests, Sitobion avenae, Hyalopterus pruni and Brevicoryne brassicae were identified by GC/MS studies. The main components found were triacylglycerols with one hexanoyl group. Fatty acid composition and position of triacylglycerols were determined from mass spectra. There was a trace of triacylglycerol with the E,E-2,4- hexadienoyl group in the extract of Brevicoryne brassicae. A series of hydrocarbons and free fatty acids were identified. Single components of straight chain aldehyde (C30) and alcohol (C32) were detected in the lipids of H. pruni, B. brassicae. Free fatty acids, including these found in the aphid lipids, were subjected to fungi-insect ecological studies. A homologous series of acids were added individually into media used to evaluate the mycelia growth and sporulation tests of the fungi, Beauveria bassiana and Paecilomyces fumosoroseus. The tests were performed in vitro and linear mycelial growth and sporulation of fungi after 14 days were measured. For both fungi, complete inhibition was observed with pentanoic and sorbic (E,E-2,4-hexadienoic) acids at a concentration as low as 0.02% w/v in both tests. Growth stimulation effects were only observed for B. bassiana with tetradecanoic and eicosanoic acid. Inhibitions were noticed for both fungi and the strongest effects were for dodecanoic (B. b.) and eicosanoic acid (P. f.). Beside free fatty acids, no other group of chemical compounds was found in the lipids which could be involved in aphids resistance to entomopathogenic fungi.
TL;DR: In this paper, the preparation and NMR spectra for a range of spirocyclic mono-, bis-and trisquaternary ammonium salts are reported, and the energy barrier for ring-inversion of central ring with the axial and equatorial C-N + carbons of the outer two rings being non-equivalent.
Abstract: The preparation and NMR spectra for a range of spirocyclic mono-, bis- and tris-quaternary ammonium salts are reported. In the case of the tricyclic bis(ammonium)salt 7 a dynamic process is observed in the 13 C NMR spectrum and by means of a variable temperature study and MAS solid state NMR this isattributed to ring-inversion of central ring with the axial and equatorial C- N + carbons of the outer two rings being non-equivalent. The energy barrier for this inversion is determined to be 53.4 ± 0.2 kJ mol -1 .
TL;DR: The reaction of methyl 2-diazophenylacetate 1 and dimethyl αdiazobenzylphosphonate 2 with various n-H components in the presence of chiral dirhodium(II) catalysts results in N-H insertion in good yield but with little or no stereoselectivity as mentioned in this paper.
Abstract: The reaction of methyl 2-diazophenylacetate 1 and dimethyl α-diazobenzylphosphonate 2 with various N-H components in the presence of chiral dirhodium(II) catalysts results in N-H insertion in good yield but with little or no stereoselectivity.
TL;DR: In this paper, double cyclization of aryloxy-phenyl acetamides is promoted by oxalyl chloride/stannyl chloride and gives 3,4-dioxocularine and aristocularine alkaloids.
Abstract: Double cyclization of aryloxy-phenyl acetamides is promoted by oxalyl chloride/stannyl chloride and gives 3,4-dioxocularine and aristocularine alkaloids. Rearrangement of the dibenzoxepine ring prior to the second cyclization produces xanthene derivatives. The synthesized cularinoids exhibit significant activity against various tumoral cell lines.
TL;DR: Hydrogenation of the readily prepared dinitrobenzenediamines 7 followed by air oxidation affords the green colored 5,7-disubstituted-5H,12H-quinoxalino[2,3-b]phenazines 3 in good yields.
Abstract: Hydrogenation of the readily prepared dinitrobenzenediamines 7 followed by air oxidation affords the green colored 5,7-disubstituted-5H,12H-quinoxalino[2,3-b]phenazines 3 in good yields. Mechanistic rationale, compound characterisation and full experimental details are provided.
TL;DR: The attempted synthesis of the unknown 8,10,12-triazatricyclo(7.3.1.02,7)tridecatriene scaffold by cyclization (intramolecular Michael-addition) of 4-(2-aminophenyl)-2-oxo-1,2,3,4- tetrahydro-pyrimidine-5-carboxylates of type 5a is described in this paper.
Abstract: The attempted synthesis of the unknown 8,10,12-triazatricyclo(7.3.1.02,7)tridecatriene scaffold 6a by cyclization (intramolecular Michael-addition) of 4-(2-aminophenyl)-2-oxo-1,2,3,4- tetrahydro-pyrimidine-5-carboxylates of type 5a is described. The synthesis of the amino precursor 10 is achieved by microwave-promoted catalytic transfer hydrogenation of the corresponding nitro analog 9. Subsequent acid-catalyzed intramolecular Michael addition leads to the desired polycyclic scaffold 11 as a transient intermediate which spontaneously disintegrates in a retro-Michael fashion to the quinoline 13.
TL;DR: By means of an iodide-catalyzed nitrocyclopropane to 4,5-dihydroisoxazoline 2-oxide isomerization, the 1,1'-dinitro-(1,1')bi(cyclopropyl)s 5, deriving from an initial ring-opening of 3,4-dinitrothiophene 1, can be stereospecifically converted into the bisnitronates 6.
Abstract: By means of an iodide-catalyzed nitrocyclopropane to 4,5-dihydroisoxazoline 2-oxide isomerization, the 1,1'-dinitro-(1,1')bi(cyclopropyl)s 5, deriving from an initial ring-opening of 3,4-dinitrothiophene 1, can be stereospecifically converted into the bisnitronates 6. From these, successive N-oxide reduction (P(OMe)3/dioxane) and aromatization (DDQ/toluene) provide convenient access to the interesting 4,5,4'5'-tetrahydro(3,3')bi-isoxazolyls 7, and (3,3')bi- isoxazolyls 8, respectively.
TL;DR: In this paper, a synthesis of thiazolo(5,4-c)quinolinone derivatives featuring the use of two different hypervalent iodine reagents has been achieved starting from ethyl benzoylacetate in an efficient way.
Abstract: A synthesis of thiazolo(5,4-c)quinolinone derivatives featuring the use of two different hypervalent iodine reagents has been achieved starting from ethyl benzoylacetate in an efficient way. Hydroxy(tosyloxy)phenyliodine (HITB, Kosers reagent) has been employed to functionalize the starting β-ketoester 4, and phenyliodine(III)bis(trifluoroacetate) (PIFA) to perform a ring closure reaction on the corresponding N-methoxyamides 9 and 14.
TL;DR: In this article, the reaction of allylic carboxylates (allyl-OZ, OZ: acetate, chloroacetate, trifluoroacetate), substituted benzoates, carbonate) with Pd 0 complexes ligated by monodentate (PPh3) or bidentate (dppb, dppf) ligands is a reversible multistep reaction, which eventually gives in DMF a cationic (η 3 -allyl)Pd II (P P) + complex with ZO −
Abstract: The reaction of allylic carboxylates (allyl-OZ, OZ: acetate, chloroacetate, trifluoroacetate, substituted benzoates, carbonate) with Pd 0 complexes ligated by monodentate (PPh3) or bidentate (dppb, dppf) ligands is a reversible multistep reaction, which eventually gives in DMF a cationic (η 3 -allyl)Pd II (P P) + complex with ZO − as the counter anion (free ions). The formation of an intermediate neutral complex (η 2 -allyl-OZ)Pd 0 (P P) where the Pd 0 is ligated to the C=C bond of the allylic carboxylate (complexation step) has been evidenced kinetically in the case of moderate OZ leaving groups (acetate, benzoates) for monodentate and bidentate phosphine ligands. The overall equilibrium constants and the rate constants of the complexation and oxidative addition-ionization steps (when not too fast) have been determined in DMF. With very good leaving groups (carbonate, trifluoroacetate), the oxidative addition-ionization step is faster than the complexation step whereas the oxidative addition-ionization step is the slowest step for less good leaving groups (acetate, benzoate). The forward rate constant of the equilibrium in which the active Pd 0 (PPh3)2 is formed from Pd 0 (dba)(PPh3)2 has been determined.
TL;DR: In this paper, the stereocontrolled synthesis of enalapril was reported, and the key transformation of the synthesis is a formal carboxylation of imines, which lies in the sequence.
Abstract: The stereocontrolled synthesis of the Angiotensin Converting Enzyme (ACE) inhibitor enalapril is reported. The key transformation of the synthesis is a formal carboxylation of imines, which lies in the sequence: imine-ketene (2+2) cycloaddition reaction, ring expansion of the resulting 3- hydroxy β-lactam to a N-carboxy α-amino acid anhydride (NCA), and final opening of the NCA with alcohols.
TL;DR: In this paper, a graph for the quantitative treatment of ketone reductions through a parallel kinetic resolution has been developed, which can be applied to a hypothetical iterative process, so that a prediction of its viability can be done.
Abstract: Equations and useful graphs for the quantitative treatment of ketone reductions through a parallel kinetic resolution have been developed. They can be applied to a hypothetical iterative process, so that a prediction of its viability can be done.
TL;DR: In this paper, a detailed explanation of the observed photochemical reactivity of 3-heteroaryl-acrylates is furnished on the basis of a comprehensive review of the photochemical dimerizations of this type of compounds.
Abstract: A detailed explanation of the observed photochemical reactivity of 3-heteroaryl-acrylates is furnished on the basis of a comprehensive review of the photochemical dimerizations of this type of compounds. The reactions occurred in the triplet state of the reagents showing good regio- and stereoselectivities. The regioselectivity can be explained assuming that the dimerization reaction is frontier orbitals controlled. The reaction of the triplet state of a reagent with another molecule of the reagent leads to the formation of the most stable biradical. This behavior induces a control in the relative stereochemistry of the two ester functions. The following cyclization occurs in order to obtain the products under kinetic control. This cyclization allows the formation of the most stable isomers.
TL;DR: The TiCl4-NR3 reagent system is useful for carbon-carbon bond forming reactions such as the aldol and related condensation reactions, the diastereoselective coupling of phenyl acetic acid derivatives, the conversion of aryl alkyl ketimines and ketoximes to pyrroles, ketazines to dihydrodiazines, enamines to aromatic amines, N,N-dialkylanilines to the corresponding benzidine derivatives, trialkylamines to unsaturated aldehydes, diarylcyclob
Abstract: The TiCl4-NR3 reagent system is useful for carbon-carbon bond forming reactions such as the aldol and related condensation reactions, the diastereoselective coupling of phenyl acetic acid derivatives, the conversion of aryl alkyl ketimines and ketoximes to pyrroles, ketazines to dihydrodiazines, enamines to aromatic amines, N,N-dialkylanilines to the corresponding benzidine derivatives, trialkylamines to unsaturated aldehydes, diarylcyclobutanones, diarylcyclobutylamine derivatives via iminium ion intermediates and for the reductive coupling of aromatic aldehydes, aldimines and intramolecular reductive coupling of chiral diimine derivatives. In all cases, the organic products are obtained in moderate to good yields, in singlepot operations under ambient reaction conditions. Hence, these synthetic methods have considerable synthetic potential.
TL;DR: The diketopiperazine derivative dipodazine has been synthesized via a stereoselective aldol condensation from N-protected indole-3-carboxaldehyde and 1,4-diacetyl-2,5-piperazinedione in the presence of cesium carbonate.
Abstract: The diketopiperazine derivative dipodazine (1), isolated from Penicillium dipodomyis, has been synthesized via a stereoselective aldol condensation from N-protected indole-3-carboxaldehyde and 1,4-diacetyl-2,5-piperazinedione (3) in the presence of cesium carbonate.
TL;DR: The present account describes recent progress in the chemistry related to myo-inositol orthoesters, which has emerged as convenient intermediates for the synthesis of inositol derivatives.
Abstract: There has been a revival of interest in the chemistry of cyclitols in the recent past due to the discovery of phosphoinositol based signal transduction mechanisms in eukaryotic systems. Traditionally, synthesis of inositol derivatives involved the protection of its hydroxyl groups as the corresponding ketals. However, recently orthoesters of myo-inositol have emerged as convenient intermediates for the synthesis of inositol derivatives. The present account describes recent progress in the chemistry related to myo-inositol orthoesters.
TL;DR: In this paper, the Baylis−Hillman coupling of various aldehydes with activated olefins is described, viz. methyl acrylate, acrylonitrile and acrolein.
Abstract: Application of methanolic trimethylamine, the tertiary amine containing minimum number of carbon atoms with lowest possible molecular weight, for mediating the Baylis−Hillman coupling of various aldehydes with activated olefins viz. methyl acrylate, acrylonitrile and acrolein is described.
TL;DR: In this article, a dienophile was added to several cyclic and acyclic conjugated dienes at room temperature to give derivatives of the 1-azabicyclo(4.1.0)hept-3-ene ring system.
Abstract: Benzyl 2H-azirine-3-carboxylate 1b added as a dienophile to several cyclic and acyclic conjugated dienes at room temperature to give derivatives of the 1-azabicyclo(4.1.0)hept-3-ene ring system. The cycloaddition reactions gave exclusively the products of endo addition with respect to the three membered ring, as shown by crystal structures of two of the compounds, 4c and 4d. Methods for the cis-hydroxylation of the double bonds of some of these compounds were explored and four dihydroxy compounds were isolated from the adducts with cyclohexa-1,3- diene, 1-acetoxybutadiene,