Palladium-catalyzed C-O bond formation: direct synthesis of phenols and aryl/alkyl ethers from activated aryl halides

A simple and efficient palladium-catalyzed carbon-oxygen bond formation is reported. The palladium-tri-tert-butylphosphine complex was found to be effective in converting haloarenes to corresponding substituted phenols. This methodology offers a direct transformation of aryl halides to phenols, as well as the straightforward application to generate a wide variety of diaryl or alkyl/aryl ethers.     

Coulometrisches Verfahren zur Bestimmung von Gesamt-, Carbonat- und Nichtcarbonat-Kohlenstoff in magmatischen, metamorphen und sediment?ren Gesteinen

Zusammenfassung Für die Bestimmung von Gesamt-, Carbonat- und Nichtcarbonat-Kohlenstoff in magmatischen, metamorphen und sedimentären Gesteinen (auch bei höheren Anteilen an organischem C) ist ein Verfahren nach dem Prinzip der coulometrischen Titration geeignet. Der Gesamt-Kohlenstoff wird ermittelt durch Erhitzung der auf <0,125 mm zerkleinerten Probe bei etwa 1250°C im Sauerstoffstrom ohne irgendwelche Zusätze. Zur Bestimmung von Nichtcarbonat-Kohlenstoff wird eine bestimmte Menge Gesteinspulver mit Salzsäure versetzt und auf einem Aluminiumblock HCl abgeraucht. Der Carbonat-Kohlenstoff entweicht als CO₂. Zurück bleibt der Nichtcarbonat-Kohlenstoff, welcher wie der Gesamt-Kohlenstoff coulometrisch bestimmt wird. Der Carbonat-Kohlenstoff bzw. die äquivalente Menge CO₂ ergibt sich dann aus der Differenz von Gesamt- zu Nichtcarbonat-Kohlenstoff. Das Verfahren ist anwendbar auf Kohlenstoffgehalte in Gesteinen von etwa 10 ppm bis 20 Gew.-% bei mittleren Standardabweichungen von etwa 0,0002–0,05% C (Richtwerte). Die Analysendauer für eine Probe beträgt etwa 3–5 min.

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Coulometric method for the determination of total, carbonate, and non-carbonate carbon in igneous, metamorphic, and sedimentary rocks

For the measurement of total carbon the sample, ground finer than 0.125 mm and without the addition of any reagents, is ignited in a current of oxygen at about 1250°C. Non-carbonate carbon can be analysed after another portion of the sample is treated with conc, hydrochloric acid and evaporated on a hot plate; the carbonates are decomposed and the carbonate carbon is removed as carbon dioxide. The residue is non-carbonate carbon which is also determined by the coulometric method. The difference between total carbon and non-carbonate carbon corresponds to carbonate carbon or its equivalent as carbon dioxide. The method is applicable to carbon contents in rocks from 10 ppm to 20 wt.-%. The standard deviation is approximately 0.0002 to 0.05% C. Each carbon analysis takes about 3 to 5 min.

     

Synthesis of unsymmetrical 2,4-dialkylpyrazolo[1,5-a]-1,3,5-triazines

The reaction of 3-aminopyrazole with imidate esters such as ethyl acetimidate, gave N-(pyrazol-3-yl)acetamidine (1) rather than the isomeric 2-acetamidoyl-3-aminopyrazole. Ring closure of 1 with orthoesters such as ethyl propionimidate, afforded unsymmetrically substituted 2.4-dialkylpyrazolo[1,5-a]-1,3,5-triazines such as 4-ethyl-2-methylpyrazolo[1,5-a]-1,3,5-triazine (3). The structure of 1 was confirmed by several alternate syntheses. The unique feature of this two-step synthetic approach to the synthesis of pyrazolo[1,5-a]-1,3,5-triazines is that it is a convenient method of preparing fused triazines based on available pyrazoles rather than the less accessible dialkyltriazines.     

REACTIVITY OF SINGLET OXYGEN TOWARD LARGE PEPTIDES

Abstract— The reactions of singlet oxygen, ¹O₂, with amino acids and their derivatives have been studied previously. It was found that only five amino acid residues interact readily with ¹O₂. Here we describe its reactions with the large peptides melittin, neuropeptide Y (NPY) and insulin in their native and in their denatured forms. The singlet oxygen quenching by a polypeptide was compared with that of a solution at the same concentration as those of its constituent amino acids, which are known to react efficiently with ¹O₂. It was found that the quenching rate by such a mixture exceeded that of the polypeptides in their native form. The ratio of the rate constants for NPY to that of the corresponding amino acid mixture in solution was 0.75. For melittin in its monomeric form it was 0.83 and for a tetramer of melittin (at high ionic strength) it was 0.70. For native insulin the ratio of the rate constants was 0.55. For oxidized insulin with its -S-S- bridges opened the figure became 0.80. However, the quenching by all the polypeptides in their fully denatured form (in the presence of 6 M urea) equalled that of the corresponding amino acid mixtures. Although polypeptides are generally supposed not to possess a stable secondary structure in solution the effects are explained by shielding of some of the reactive amino acid residues in the chain by temporary folding or incipient secondary structures of the native polypeptide.
It is shown that the kinetics for a homogeneous solution of quenchers applies also to measurements in a polypeptide solution where the quenchers are localized along the polypeptide backbone and thus form clusters in solution.     

Synthesis of 3‐aroyl‐4‐(3‐chromonyl)‐2‐pyrazolines

New 3‐aroyl‐4‐(3‐chromonyl)‐2‐pyrazolines have been synthesized by the reaction of 3‐(3‐aryl‐3‐oxo‐propenyl)chromen‐4‐ones and diazomethane. Some of these 2‐pyrazolines have also been N‐acylated with a mixture of anhydrous pyridine and acetic anhydride or propionic anhydride. Structures of all new compounds have been elucidated by elemental analyses, mass spectrometry, ir and nmr spectroscopic measurements.     

INDUCTION OF FREE RADICALS IN DNA BY PROFLAVINE AND VISIBLE LIGHT: INFLUENCE OF OXYGEN AND IONIC STRENGTH

Abstract —The photosensitization of native DNA is observed as an induction of free radicals in the DNA moiety of proflavine-DNA complexes. The intensity of the electron paramagnetic resonance spectra (at 77 K) is a measure of the number of free radicals present in frozen solutions of DNA-proflavine complexes after irradiation with visible light (Λ > 320 nm). In the absence of O₂, the photosensitization is significant but very low; it increases slightly with increasing NaCl ionic strength; it appears to be due to intercalated dye molecules and the qualitative analysis of the spectra obtained shows that mainly thymidine is involved. The reaction measured after saturation with O₂ is the same as the reaction in air but is quantitatively higher; the free radicals observed are peroxides. This induction of free radicals appears to be due to the intercalated dye molecules, each molecule acting independently. The important observation is a very sharp and large (around a hundred-fold) increase in the photosensitizing efficiency of the bound dye molecules occurring in NaCl between μ, # 0–25 and μ= 0–5 and in MgCl₂ between μ# 0–01 and μ=0–1.     

Trapping tetramethoxyzincate and -cobaltate(II) between Mo24+ units

Two compounds of a new type, [Mo(2)](CH(3)O)(2)M(CH(3)O)(2)[Mo(2)] where [Mo(2)] is an abbreviation for Mo(2)[(p-MeOC(6)H(4))NCHN(p-MeOC(6)H(4))](3) and M = Zn (1) and Co (2), are reported. Discrete [M(OR)(4)](2-) ions, either as such or in the mu(2),eta(4) role, have not heretofore been described. In these compounds they have distorted tetrahedral structures and bridge two [Mo(2)] groups in much the same way as did SO(4)(2-), MoO(4)(2-), and WO(4)(2-) ions in other recently reported compounds (Cotton, F. A.; Donahue, J. P.; Murillo, C. A. Inorg. Chem. 2001, 40, 2229). The (1)H NMR spectrum of 1 and the visible spectrum and magnetic properties of 2 are consistent with these structures. The M(OCH(3))(4) bridges are moderately effective in coupling the two [Mo(2)] redox centers. Compounds 1 and 2 may also be viewed as having Zn(II) and Co(II) centers tetrahedrally coordinated by the bidentate ligand [Mo(2)[(p-MeOC(6)H(4))NCHN(p-MeOC(6)H(4))](3)(OMe)(2)](-). From that point of view they may be compared with Zn(DPM)(2) and Co(DPM)(2) (3), where DPM is the anion of dipivaloylmethane. For purposes of comparison, 3 has been fully characterized structurally, spectroscopically, and magnetically. Close analogies between 2 and 3 are shown to exist.     

Notiz über einen Zugang zu β, γ-ungesättigten Carbonsäurederivaten mit Hilfe der Amidacetal-Claisenumlagerung. Über synthetische methoden, 17. Mitteilung

Note on a preparation of β, γ-unsaturated carboxylic acid derivatives using the amide acetal Claisen rearrangement 3-(Trimethylsilyl)allyl alcohols smoothly undergo the amide acetal Claisen rearrangement furnishing allyl silanes. Subsequent protolysis with HF at ?20° provides a convenient, stereoselective method for the preparation of β, γ-unsaturated carboxylic acid derivatives. Three model examples illustrate the procedure.     

Nitration studies of naphtho[2,3-c][1,2,5]thiadiazole

Nitration of naphtho[2,3-c][1,2,5]thiadiazole gives the 5-nitro derivative in 61–66% yield. Chlorination of this product apparently gives an unstable addition product which loses hydrogen chloride on recrystallization to give 4-chloro-8-nitronaphtho[2,3-c][1,2,5]thiadiazole. Thus, naphtho[2,3-c][1,2,5]thiadiazole under nitrating conditions behaves as a 2-substituted naphthalene rather than as an anthracene analog.