Triflamidation of Allyl-Containing Substances:Unusual Dehydrobromination vs. Intramolecular Heterocyclization

Allyl halides with triflamide under oxidative conditions form halogen-substituted amidines. Allyl cyanide reacts with triflamide in acetonitrile or THF solutions in the presence of NBS to give the products of bromotriflamidation with a solvent interception, whereas in CH₂Cl₂ two regioisomers of the bromotriflamidation product without a solvent interception were obtained. The formed products undergo base-induced dehydrobromination to give linear isomers with the new C=C bond conjugated either with the nitrile group or the amidine moiety or alkoxy group. Under the same conditions, the reaction of allyl alcohol with triflamide gives rise to amidine, which was prepared earlier by the reaction of diallyl formal with triflamide. Unlike their iodo-substituted analogs, bromo-substituted amidines successfully transform into imidazolidines under the action of potassium carbonate.     

Photo-Induced Reactions between Glyoxal and Hydroxylamine in Cryogenic Matrices

In this paper, the photochemistry of glyoxal–hydroxylamine (Gly–HA) complexes is studied using FTIR matrix isolation spectroscopy and ab initio calculations. The irradiation of the Gly–HA complexes with the filtered output of a mercury lamp (λ > 370 nm) leads to their photoconversion to hydroxyketene–hydroxylamine complexes and the formation of hydroxy(hydroxyamino)acetaldehyde with a hemiaminal structure. The first product is the result of a double hydrogen exchange reaction between the aldehyde group of Gly and the amino or hydroxyl group of HA. The second product is formed as a result of the addition of the nitrogen atom of HA to the carbon atom of one aldehyde group of Gly, followed by the migration of the hydrogen atom from the amino group of hydroxylamine to the oxygen atom of the carbonyl group of glyoxal. The identification of the products is confirmed by deuterium substitution and by MP2 calculations of the structures and vibrational spectra of the identified species.     

Enantioselective Protonation of Cyclic Carbonyl Ylides by Chiral Lewis Acid Assisted Alcohols

Chiral Lewis acid-catalyzed asymmetric alcohol addition reactions to cyclic carbonyl ylides generated from N-(α-diazocarbonyl)-2-oxazolidinones featuring a dual catalytic system are reported. Construction of a chiral quaternary heteroatom-substituted carbon center was accomplished in which the unique heterobicycles were obtained in good yields with high stereoselection. The alcohol adducts were successfully converted to optically active oxazolidine-2,4-diones by hydrolysis. Mechanistic studies by DFT calculations revealed that alcohols could be activated by Lewis acids, enabling enantioselective protonation of the carbonyl ylides.     

Building C(sp3) Molecular Complexity on 2,2′-Bipyridine and 1,10-Phenanthroline in Rhenium Tricarbonyl Complexes

The reactions of [Re(N-N)(CO)₃(PMe₃)]OTf (N-N=2,2′-bipyridine, bipy; 1,10-phenanthroline, phen) compounds with tBuLi and with LiHBEt₃ have been explored. Addition to the N-N chelate took place with different site-selectivity depending on both chelate and nucleophile. Thus, with tBuLi, an unprecedented addition to C5 of bipy, a regiochemistry not accessible for free bipy, was obtained, whereas coordinated phen underwent tBuLi addition to C2 and C4. Remarkably, when LiHBEt₃ reacted with [Re(bipy)(CO)₃(PMe₃)]OTf, hydride addition to the 4 and 6 positions of bipy triggered an intermolecular cyclodimerization of two dearomatized pyridyl rings. In contrast, hydride addition to the phen analog resulted in partial reduction of one pyridine ring. The resulting neutral Re^I products showed a varied reactivity with HOTf and with MeOTf to yield cationic complexes. These strategies rendered access to Re^I complexes containing bipy- and phen-derived chelates with several C(sp³) centers.     

Distorted Porphyrins with High Stability: Synthesis and Characteristic Electronic Properties of Mono- and Di-Nuclear Tricarbonyl Rhenium Tetraazaporphyrin Complexes

Mono- and di-nuclear tricarbonyl Re(I) tetraazaporphyrin complexes ( Re₁TAP and Re₂TAP ) are investigated and compared with Re(I) phthalocyanine complexes ( Re₁Pc and Re₂Pc ). Although Re₂Pc is unstable in polar solvents, and easily undergoes demetallation reaction, the coordination of the TAP ligand significantly improves the tolerance toward polar solvents, affording more stability to Re₂TAP . Additionally, the incorporation of [Re(CO)₃]⁺ unit(s) and the TAP ligand results in remarkable positive shifts in both oxidation and reduction potentials. Consequently, the more positive oxidation potentials of the ReTAP complexes significantly increase the tolerance toward oxidation, while the reduction potential indicates that Re₂TAP is suitable for a soluble electron acceptor. In contrast to Re₁Pc and Re₂Pc , Re₁TAP and Re₂TAP show unique broad Q bands, which can be attributed to the admixture of the π-π* and metal-to-ligand charge transfer characters, owing to the lowered π orbital energy in the TAP complexes. This study is useful for controlling electronic properties and realizing high stability in Pc analogues.     

Determination Of Formaldehyde And Acetaldehyde Associated To Atmospheric Aerosols By HPLC

Abstract

A rapid new analytical protocol was developed for the determination of formaldehyde and acetaldehyde associated to atmospheric particulate matter, at ng/m³ levels. The aerosols were collected on glass fiber filters (8″×10″) at face velocities ranging from 15 m/min to 23 m/min. Aliquots of 15.4 cm² were sonicated, for 20 min, with 5.0 mL of 0,01% 2,4-dinitrophenylhydrazine (DNPH), 1 % phosphoric acid. The liquid phase was then filtered and the separation and quantification of the corresponding 2,4-dinitrophenylhidrazone (DNPHo) derivatives carried out by reverse phase HPLC. Acetonitrile:water (57:43, v/v) as mobile phase at 1.0 mL/min and absorbance detection at 350 nm and 365 nm for, respectively, formaldehyde-DNPHo (0.04 AUFS) and acetaldehyde-DNPHo (0.01 AUFS) were used. The precision for four different aliquots, from a 8″×10″ glass fiber filter, were under 0.04% for formaldehyde and 14.16 % for acetaldehyde. In Salvador, Bahia, Brazil, formaldehyde and acetaldehyde were determined, respectively, in the range of 6.8 ng/m³ to 27.3 ng/m³ and 9.1 ng/m³ to 54.6 ng/m³.     

A New Bismuth Nitrate–Catalyzed Electrophilic Substitution of Indoles with Carbonyl Compounds Under Solvent-Free Conditions

An expeditious synthetic method for the preparation of bis(indollyl)methane derivatives has been developed through a bismuth nitrate-catalyzed reaction of indole with various carbonyl compounds in mortar and pastle under solvent-free conditions.     

Preparation of Silica-Bonded S-Sulfonic Acid: A Recyclable Catalyst for the Synthesis of Bis-Indolylmethanes

Silica bonded S-sulfonic acid (SBSSA) was prepared by the reaction of 3-mercaptopropylsilica (MPS) and chlorosulfonic acid in chloroform. Silica-bonded S-sulfonic acid, as a reusable solid acid catalyst, was used for the condensation reactions of indole with carbonyl compounds at ambient temperature. Tetra-(indolyl)methanes were also obtained by the condensation reaction of indole with dialdehyde compounds. Silica bonded S-sulfonic acid was recovered and reused.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

On The Fluorometric Method for the Measurement of β-Cyanoalanine Synthase Activity

Abstract

A modification of a fluorescence assay method for β-cyanoalanine synthase has been described which involves the direct coupling of the product of cyanide and cysteine to resazurin, to produce the fluorescent resosurfin, The fluorescence produced was found to be directly proportional to the rate of the reaction.