Size-dependent luminescence of boron difluoride β-diketonates

Size-dependent luminescence properties of boron difluoride β-diketonates were detected. Most compounds investigated are characterized by noticeable hypsochromic shifts of luminescence band maxima on going from bulk crystals to microcrystals. However, a decrease in the crystal size of (dibenzoylmethanato)boron difluoride with unique supramolecular structure was accompanied by a bathochromic shift of the luminescence band maximum. Size-dependent luminescence properties of complexes examined were analyzed in the framework of excitonic mechanism. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1168–1170, June, 2008.     

First mesogenic derivative of boron difluoride β-enaminoketonate

Boron difluoride complexes possessing liquid crystalline and luminescent properties were synthesized for the first time on the basis of non-mesogenic β-enaminoketones.     

Photoinduced excimer formation of boron difluoride β-diketonates in poly(methyl methacrylate)

Russian Chemical Bulletin - The photochemical behavior of β-diketonates of boron difluoride in poly(methyl methacrylate) was studied. Excimers of boron chelates are formed in the course of UV...     

Synthesis ofα-substitutedα-amino acids by the alkylation of 5-oxazolinone derivatives

Methods have been developed for the alkylation of 5-oxazolinone derivatives in DMF in the presence of K₂CO₃, KOH, or diisopropylethylamine and a phase transfer catalyst as well as for the preparation of-methyl-phenylalanine,-methylalanine,-methylalanine, and the methyl ester of N-benzoyl--methylalanine. Increasing the initial concentration of the starting 5-oxazolinone in the reaction mixture leads to a sharp drop in the yield of reaction products due to side condensation reactions. The reaction of 2-phenyl-4-benzyl-5- oxazolinone with ethyl iodide gave a dimer namely, 3-(benzoylamino)-3,5-dibenzylpyrrolidine-2,4-dione.Latvian Institute of Organic Chemistry, LV-1006 Riga. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 829–833, June, 1994. Original article submitted January 21, 1994.     

Asymmetric synthesis of anti-α-substituted β-amino ketones from sulfinimines

Previously unknown, enantiopure, β-amino ketones were prepared in modest yield by addition of lithium reagents to N-sulfinyl anti-α-substituted β-amino Weinreb amides. Grignard reagents failed to add to these Weinreb amides in contrast to the syn-α-substituted isomers which did. The anti-α-substituted β-amino Weinreb amides were prepared by addition of LiN(OMe)Me to the corresponding N-sulfinyl anti-α-substituted β-amino esters because α-alkylation of N-sulfinyl β-amino Weinreb amide enolates resulted in poor diastereoselectivities.     

Synthesis of (α-substituted α-aminophosphinic and α-aminophosphonic acids

The reaction of ketoximes with hypophosphorous acid resulted in previously unknown -substituted--aminophosphinic acids, which were oxidized into the corresponding -substituted--aminophosphonic acids.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2729–2732, November, 1996.     

Catalytic asymmetric boron–boron addition to unsaturated molecules

In this paper, we present representative examples of metal-catalyzed asymmetric boron–boron addition to CC and describe chiral organoboron synthesis as a suitable method for preparing chiral-functionalized compounds.     

Crystal structure of boron difluoride 1-naphthylbutanedionate-1,3(C10H7COCHCOCH3BF2). π-stacking interaction and luminescence

The crystal structure and luminescent properties of boron difluoride 1-naphthyl-butandionate-1,3 (1) (C₁₀H₇COCHCOCH₃BF₂) are determined and analyzed. The molecules of compound 1 are packed in the crystal into infinite stacks due to π-stacking interactions. A feature of the structure of 1 is a fragment of four neighboring molecules, the π-systems of which participate in π…π interactions of different types: naphthyl…naphthyl (head-to-head) and naphthyl…chelate (head-to-tail). The data of time resolved luminescent spectroscopy and quantum chemical computations show that in crystals and concentrated solutions of 1, one excimer structure occurs corresponding to the head-to-tail overlap.     

Enantio- and diastereoselective synthesis of 4′-α-substituted carbocyclic nucleosides

Enantio- and diastereoselective synthesis of 4-α-alkylcarbovir derivatives 5 were achieved based on Sakai's asymmetric alkylation of β-keto esters. The key carbocyclic intermediate 14 was synthesized from 8 via an eleven-step sequence. Coupling of 14 with 2-amino-6-chloropurine followed by desilylation and subsequent hydrolysis gave the target compounds 5 in moderate yields.     

The complex spectrum of a "simple" free radical: the Ã-X̃ band system of the jet-cooled boron difluoride free radical

The near-ultraviolet band system of the jet-cooled boron difluoride free radical has been studied by a combination of laser-induced fluorescence and single vibronic level wavelength resolved emission spectroscopies. The radical was produced in a supersonic discharge jet using a precursor mixture of 1%-3% of BF(3) or (10)BF(3) in high pressure argon. A large number of bands were found in the 340-286 nm region and assigned as transitions from the X?(2)A(1) ground state to the lower Renner-Teller component of the A?(2)Π excited state, based on our previous ab initio potential energy surface predictions, matching the emission spectra Franck-Condon profiles of (11)BF(2) and (10)BF(2), and comparison of observed and calculated boron isotope effects. Several bands have been rotationally analyzed providing ground state structural parameters of r(0)(') (BF) = 1.3102(9) ? and θ(0)(') (FBF) = 119.7(6)°. The ground state totally symmetric vibrational energy levels of both boron isotopologues have also been measured and assigned up to energies of more than 8000 cm(-1). Although BF(2) might be considered to be a "simple" free radical, understanding the details of its electronic spectrum remains a major challenge for both theory and experiment.     

Hydroxymethylation of α-substituted nitroacetates

Only 1 mol % of K₃PO₄ is efficient enough to catalyze the hydroxymethylation of α-substituted nitroacetates in good to excellent yield. Both aliphatic and aryl substituted nitroacetates work well under this reaction. The first catalytic asymmetric version of this reaction also reported that 10 mol % of cupreidine could catalyze this reaction up to 71% ee and 89% yield. Paraformaldehyde and formalin could both serve as the hydroxymethylation C1 unit. The synthetic application of products is also demonstrated.     

Synthesis of a chiral phosphonium salt for the preparation of α-substituted alaninol derivatives

We herein report the synthesis of a chiral phosphonium salt, {[(4S)-4-methyl-2-oxo-1,3-oxazolidin-4-yl]methyl}(triphenyl)phosphonium iodide 13 to provide a new Wittig reagent for the general method of synthesizing α-substituted alaninol derivatives. Our method described here is widely applicable to reactions with various types of aldehyde to afford olefin products with high E-selectivity, enabling us to provide a new approach to the synthesis of chiral S1P₁ agonists including our key intermediates, and of the trace amine-associated receptor 1 (TAAR1) agonist.     

Synthesis and transformations of the 20-substituted derivatives of 16α,17α-epoxy-5α-pregnane-3Β,21-diol-20-ones

A new and more effective sequence of reactions is proposed for the production of 16,17-isopropylidenedioxy-5-pregnane-3,21-diol-20-one. It uses methods previously unused for 5-H-steroids and involves 21-hydroxylation of 16,17-epoxy-5-pregnan-3-ol-20-one with diacetoxyiodobenzene and cis-opening of the obtained 21-hydroxy-16,17-epoxy-5-pregnane-3,21-diol-20-one by acetic acid in the presence of epoxycarbonylhydrazine, followed by condensation of the obtained product with acetone.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1185–1188, May, 1991.     

Modeling of the Electronic Absorption Spectra and Photoionization of Scandium and Titanium Tris(acetylacetonates) by the DV-XαMethod

In order to interpret the electronic absorption spectra of titanium tris(-diketonates) and to establish the correlation between the ionization and excitation energies, the oscillator strengths and energies and the ionization energies for the model complexes M(Mal)₃(Mal is deprotonated malonodialdehyde, M = Sc, Ti) were calculated in the transition state approximation of the DV-Xmethod. The good agreement between the calculated photoelectron spectra and the experimental data and the correlation found between two types of excitation justified the assignment of the experimental absorption bands to the electronic states of Ti(Acac)₃.     

Li- and Mg-doping into icosahedral boron crystals, α- and β-rhombohedral boron, targeting high-temperature superconductivity: structure and electronic states

The possibility of high T_C superconductivity is suggested for lithium- and magnesium-doped icosahedral boron crystals, α- and β-rhombohedral boron. The doping of these elements was attempted by a vapor diffusion processing. Both lithium and magnesium are hardly doped into the α-rhombohedral boron, although small amounts of metallic parts are found in the sample. In only one Li-doped sample, the metallic part contained 0.02 vol% of the superconductive phase (T_C∼36 K). Magnesium was successfully doped into β-rhombohedral boron homogeneously up to 4 at% (Mg_4.1B₁₀₅), although considerable amount of impurity silicon was introduced together with magnesium. The structures of the doped samples were analyzed assuming co-doping of magnesium and silicon. The relation between the site occupancies of the dopants and the lattice expansion is discussed. The estimation of the density of states near the Fermi energy by EELS and magnetic susceptibility measurements suggested a metal transition of the β-rhombohedral boron by the doping of magnesium and silicon. The relation between the metal transition and the intrinsic acceptor level is also discussed.     

Expedient synthesis of α-substituted fluoroethenes

A mild and efficient synthesis of 1-aryl-1-fluoroethenes from benzothiazolyl (aryl)fluoromethyl sulfones and paraformaldehyde, under DBU- or Cs(2)CO(3)-mediated conditions at room temperature, is described. A comparable diethyl fluoro(naphthalen-2-yl)methylphosphonate reagent does not react with paraformaldehyde under these mild conditions. The utility of the methodology for synthesis of terminal α-fluoroalkenes bearing electron-withdrawing functionalities is also shown.     

Oxidation properties of β-substituted pyrroles

Pyrroles represent building blocks of conjugated poly(heterocycles) which, as organic conductors, are potential materials for organic electronics. Oxidation of β-substituted pyrroles constitutes an important first step in the process of electropolymerization. Ionization energy and the electron spin density distribution are two the most important properties regarding monomers. These properties are studied as a function of electron-withdrawing and electron-donating substituents of pyrrole ring. Evolution of molecular structure, nature of bonding, and electronic density are studied as an effect of ionization process.     

Charge delocalization in a homologous series of α,α'-bis(dianisylamino)-substituted thiophene monocations

A homologous series of three molecules containing thiophene, bithiophene, and terthiophene bridges between two redox-active tertiary amino groups was synthesized and explored. Charge delocalization in the one-electron-oxidized forms of these molecules was investigated by a combination of cyclic voltammetry, near-infrared optical absorption spectroscopy, and EPR spectroscopy. All three cation radicals can be described as organic mixed-valence species, and for all of them the experimental data are consistent with strong delocalization of the unpaired electron. Depending on what model is used for analysis of the optical absorption data, estimates for the electronic coupling matrix element (H(AB)) range from ～5000 to ～7000 cm(-1) for the shortest member of the homologous series. According to optical absorption and EPR spectroscopy, even the terthiophene radical appears to belong either to Robin-Day class III or to a category of radicals commonly denominated as borderline class II/class III systems. The finding of such a large extent of charge delocalization over up to three adjacent thiophene units is remarkable.