(Tosylimino)phenyl-λ3-iodane as a reagent for the synthesis of methyl carbamates via Hofmann rearrangement of aromatic and aliphatic carboxamides

A new, mild procedure for the Hofmann rearrangement of aromatic and aliphatic carboxamides using (tosylimino)phenyl-λ(3)-iodane, PhINTs, as a reagent is reported. Because of the mild reaction conditions, this method is particularly useful for the Hofmann rearrangement of substituted benzamides, which usually afford complex reaction mixtures with other hypervalent iodine oxidants. The mild reaction conditions and high selectivity in the reaction of carboxamides with PhINTs allow the isolation of the initially formed labile isocyanates or their subsequent conversion to stable carbamates by treatment with alcohols.     

Kinetic studies of the fluorination of uranium oxides by fluorine—I: The fluorination of U3O8 and UO3

The reactions of U₃O₈ and UO₃ with fluorine have been studied in the temperature range from 350 to 440°C with a thermobalance. The overall reaction consists of two steps. In the first step reaction, these oxides change to uranyl fluorides and in the second to UF₆. In the case of U₃O₈, the first step reaction influenced the rate of the second step, so that the formation of the UF₆ was slow at first, where an induction period was seen, and finally followed the linear law. The rate of the first step reaction of UO₃ was much faster than the second step, and the great part of the overall reaction followed the linear law. The activation energies of the second step reactions for U₃O₈ and UO₃ were 21·3 and 22·0 kcal/mole respectively. An almost linear relationship was found to exist between the reaction rate and the partial pressure of fluorine. For U₃O₈, the formation rate of UF₆ was nearly proportional to the surface area determined by gaseous adsorption.     

Oxidation of primary aliphatic and aromatic aldehydes with difluoro(aryl)-λ3-bromane

Oxidation of primary aliphatic aldehydes with p-trifluoromethylphenyl(difluoro)-λ(3)-bromane in dichloromethane at 0 °C afforded acid fluorides selectively in good yields, while that of aromatic aldehydes in chloroform at room temperature produced aryl difluoromethyl ethers. A larger migratory aptitude of aryl groups compared to primary alkyl groups during a 1,2-shift from carbon to an electron-deficient oxygen atom in bromane(III) Criegee-type intermediates will result in these differences in the reaction courses.     

Metal-free α-CH amination of ethers with hypervalent sulfonylimino-λ3-bromane that acts as an active nitrenoid

Hypervalent N-triflylimino-λ(3)-bromane undergoes direct and regioselective α-C-H amination of ethers at room temperature under transition metal-free conditions. Kinetic results, substituent and deuterium isotope effects suggest an asynchronous concerted organonitrenoid transition state with some hydride transfer character, analogous to that for alkane C-H insertions.     

Determination of pπ-conjugation energy in aromatic amines,ethers and sulfides by complexing method

On the basis of investigation of the heat effects of formation, dipole moments and UV-spectra of n-donors with halides of Group III metals a new method has been developed for the determination of pπ-conjugation energies in aromatic systems containing a heteroatom. The energies of pπ-conjugation of a number of aromatic amines, ethers and sulphides have been determined. The good agreement in the values obtained when using aluminium bromide, aluminium chloride, boron trifluoride and gallium trichloride as acceptors proves the correctness of the concepts which lie at the basis of the above method. The obtained values of pπ-conjugation energies make it possible to draw some conclusions pertaining to the structure of aromatic amines, ethers and sulphides.     

Kinetic studies of the fluorination of uranium oxides by fluorine—II: The fluorination of UO2

A study has been made on the fluorination of UO₂ powder and pellet to UF₆ with gaseous fluorine over the temperature range from 300 to 430°C, using the same experimental method as reported in Part 1. As same as the reaction of U₃O₈ and UO₃, the overall reaction consists of two steps. In the first step, UO₂ is converted to UO₂F₂ and in the second the UO₂F₂ is further changed to UF₆. The first step reaction is very rapid in comparison with the second step which follows the linear law. The activation energies of the second step reaction were determined for the two types of powders, active and inactive UO₂, to be 33·1 and 29·4 kcal/mole respectively. The reaction rate were approximately proportional to the partial pressure of fluorine.     

Silver-mediated fluorination of potassium aryltrifluoroborates with Selectfluor®

A simple and practical procedure for the silver-mediated fluorination of aryl- and heteroaryltrifluoroborates with electrophilic fluorine from Selectfluor^® and LiOH·H₂O is presented. The reaction procedure is simple and easy to set up, the process produces fluorinated arenes and heteroarenes in good to excellent yields and a wide range of electronically and structurally diverse substrates are tolerated.     

Palladium-catalyzed haloallylation of aromatic ynol ethers with allyl chlorides: a highly regio- and stereoselective approach to (1E)-α-chloroenol ethers

Described herein is a Pd-catalyzed haloallylation of aromatic ynol ethers and allyl chlorides, allowing facile access to (1E)-α-chloroenol ethers in a highly regio- and stereoselective manner. The synthetic utility of this method is demonstrated well by the synthesis of the stereodefined multisubstituted enol ethers and α-allylated carbonyl compounds.     

Structural and bonding aspects of molybdenum tricarbonyl complexes of 2,4,6-tritertiarybutyl-1,3,5-triphosphabenzene,P3C3But3 and some λ3,λ3,λ5- and λ3,λ5,λ5-alkylated derivatives

The molecular structure of the previously reported compound [Mo(CO)₃(η⁶-P₃C₃Bu^t₃)] has been determined by a single-crystal X-ray diffraction study. Syntheses and molecular structures are also described for the structurally related compounds [Mo(CO)₃(η⁵-P₃C₃Bu^t₃)(Me)(Buⁿ)], [Mo(CO)₃(η⁵-P₃C₃Bu^t₃)(H)(Buⁿ)] and [Mo(CO)₃(η⁴-P₃C₃Bu^t₃(Me)(Buⁿ)(H)(O)Li(THF)₃]. Density functional calculations at the B3LYP/cc-pVDZ(-PP) and BP86/cc-pVDZ(-PP) levels have been carried out on the above complexes and the nature of the bonding between the different rings and molybdenum is discussed. ³¹P NMR spectroscopic evidence is presented for the existence of the novel complex [Mo(CO)₃(η⁶-P₃C₃Bu^t₃)PtCl₂(PEt₃)] in which the triphosphabenzene ring acts as an overall 8-electron donor to the two metal centres.     

Mass spectra and organic analysis—II : Mass spectra of aromatic ethers in which the oxygen forms part of a ring

The mass spectra of a number of phenyl ethers in which the oxygen atom forms part of a heterocyclic ring have been measured. There is a strong tendency for stable aromatic heterocyclic ions to be formed without ring fission, although other fragmentation processes occur in the reduced compounds, these frequently involving ring fission and subsequent recyclization. Evidence for the existence of the dehydrotropylium and dehydrobenzene ions is presented. It is suggested that ions that are stabilized by the operation of the so-called “ortho-effect” are generally cyclic, and derivatives of one of these ions, the dioxymethylene ions of mass 122, have been examined.     

Parsing of the free energy of aromatic–aromatic stacking interactions in solution

We report an analysis of the energetics of aromatic–aromatic stacking interactions for 39 non-covalent reactions of self- and hetero-association of 12 aromatic molecules with different structures and charge states. A protocol for computation of the contributions to the total energy from various energetic terms has been developed and the results are consistent with experiment in 92% of all the systems studied. It is found that the contributions from hydrogen bonds and entropic factors are always unfavorable, whereas contributions from van-der-Waals, electrostatic and/or hydrophobic effects may lead to stabilizing or destabilizing factors depending on the system studied. The analysis carried out in this work provides an answer to the questions “What forces stabilize/destabilize the stacking of aromatic molecules in aqueous-salt solution and what are their relative importance?”     

Elemental fluorine, Part 23: Direct fluorination of β-ketoesters as an approach to enantioselective fluorination

Attempts to develop a direct enantioselective fluorination protocol using elemental fluorine and an appropriate Lewis acid and chiral ligand system are described.     

Oxidation of benzyl alcohols with difluoro(aryl)-λ-bromane: formation of benzyl fluoromethyl ethers via oxidative rearrangement

Oxidative rearrangement of benzyl alcohols with difluoro(p-trifluoromethylphenyl)-λ³-bromane (5 × 10⁻² M) in chloroform at room temperature afforded aryl fluoromethyl ethers selectively in good yields, probably via 1,2-shift of aryl groups from benzylic carbon to oxygen atoms.     

1,3λ3-Azaarsinine

The title compounds are available for the first time by O/As-exchangereaction of 1,3λ³-azapyryliumsalts with As(SiMe₃)₃.     

Highly Diastereoselective Synthesis of Anomeric β-O-Glycopyranosyl σ3λ3-and σ4λ5-Phosphorus Compounds

Abstract

A new method for the highly stereoselective synthesis of β-O-σ³λ³ and σ⁴λ⁴ phosphorus-substituted 2,3,4,6-tetrabcnzylglucose is presented. The β-diastereoselective synthesis of the carbohydrates containing σ³λ³ and σ⁴λ⁵ phosphorus groups could be accomplished via two main synthetic routes. The first involves the addition of the σ³λ³-phosphorus derivative 3 to the 2,3,4,6-tetrabenylglucose derivative 1 (αβ = 1:l) in toluene and triethylamine as a catalyst to provide the σ³λ³ phosphorus derivative 4 with practically 100% β-diastereoselectivity.     

Regio- and diastereoselective fluorination of alicyclic β-amino acids

A regio- and stereoselective approach to fluorinated β-aminocyclohexene or cyclohexane esters has been developed, starting from a bicyclic β-lactam (1). The procedure involves six or seven steps, based on regio- and stereoselective iodolactonization, lactone opening and hydroxy-fluorine exchange. The method has been extended to the synthesis of fluorinated amino ester enantiomers.     

Synthesis of α-monoglycerides of aromatic acids

The synthesis of -monoglycerides of aromatic acids has been performed by the transesterification of the methyl esters of the corresponding acids with glycerol. The structures of the compounds obtained have been confirmed by their IR, UV, and¹H and¹³C NMR spectra.A. B. Bekturov Institute of Chemical Sciences, Academy of Sciences of the Republic of Kazakhstan, Almaty, fax (3272) 61 57 65. Translated from Khimiya Prirodnykh Soedineii, No. 4, pp. 452–457, July–August, 1999.     

Mild hydrolytic cleavage of α-ferrocenylalkyl-O-methyl ethers

The conversion of α-ferrocenylalkyl-O-methyl ethers into the corresponding alcohols was successfully achieved by solvolysis in water/acetone mixtures. The content of water in the solvent markedly influenced the reaction rates. The reactivity of structurally different classes of ferrocenyl ethers was evaluated and in most cases high yields of ferrocenyl alcohols or diols were obtained in a few hours without any additive. Deprotection of less reactive substrates was accelerated in the presence of montmorillonite. The method is simple, environmentally benign and valuable in providing easy access to a variety of ferrocenyl derivatives through the use of the –O-methyl ether protective group.     

Synthesis of novel disulfide-bridged dilactam crown ethers

The novel macrocyclic dilactams with redox-switched disulfide linkage were synthesized.These compounds were obtained from 2,2'-dithiodibenzoyl chloride in the macrocyclization step by fast addition method in moderate yields.