A facile protocol for the preparation of 5-alkylidene and 5-imino substituted hydantoins from N,N′-disubstituted parabanic acids

A convenient procedure for the preparation of various substituted (thio)hydantoins is described. The method is based on Wittig and aza-Wittig reactions of parabanic acids with phosphonium ylides. The reactions occurred both regio- and stereo-selectively.     

Postfunctionalization of polyoxanorbornene via sequential Michael addition and radical thiol‐ene click reactions

We demonstrated the successful postfunctionalization of poly(oxanorbornene imide) (PONB) with two types of double bonds using sequential orthogonal reactions, nucleophilic thiol‐ene coupling via Michael addition and radical thiol‐ene click reactions. First, the synthesis of PONB with side chain acrylate groups is carried out via ring‐opening metathesis polymerization and nitroxide radical coupling reaction, respectively. Subsequently, the resulting polymer having two different orthogonal functionalities, main chain vinyl and side chain acrylate, is selectively modified via two sequential thiol‐ene click reactions, nucleophilic thiol‐ene coupling via Michael addition and photoinduced radical thiol‐ene. The orthogonal reactivity of two diverse double bonds, vinyl and acrylate functionalities, for the abovementioned consecutive thiol‐ene click reactions was first demonstrated on the model compound. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Multiarm star triblock terpolymers via sequential double click reactions

Multiarm star triblock terpolymers were obtained by using two different click reactions sequentially: Cu(I) catalyzed azide–alkyne and Diels–Alder. The synthetic strategy is described as follows: (poly(methyl methacrylate))_n‐(polystyrene)_m‐poly(divinyl benzene)) ((PMMA)_n‐(PS)_m‐polyDVB) multiarm star diblock copolymer was first obtained from an azide–alkyne click reaction of (alkyne‐PS)_m‐polyDVB multiarm star polymer with α‐anthracene‐ω‐azide PMMA (anth‐PMMA‐N₃), followed by a Diels–Alder click reaction of the anthracene groups at the star periphery with α‐maleimide poly (tert‐butyl acrylate) (PtBA‐MI) or α‐maleimide poly(ethylene glycol) (PEG‐MI) leading to target (PtBA)_k‐(PMMA)_n‐(PS)_m‐polyDVB and (PEG)_p‐(PMMA)_n‐(PS)_m‐polyDVB multiarm star triblock terpolymers. The hydrodynamic diameter of individual multiarm star triblock terpolymers were measured by dynamic light scattering (DLS) to be ～24–27 nm in consistent with the atomic force microscopy (AFM) images on silicon substrates. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1557–1564, 2010     

Perturbation theory in a framework of iteration methods

In a previous paper [J. Phys. A 36 (2003) 11807], we introduced the ‘asymptotic iteration method’ for solving second-order homogeneous linear differential equations. In this Letter, we study perturbed problems in quantum mechanics and we use the method to find the coefficients in the perturbation series for the eigenvalues and eigenfunctions directly, without first solving the unperturbed problem.     

Syntheses,characterization of and studies on the electrochemical behaviour of ferrocenyl dithiophosphonates and 4-methoxyphenyl dithiophosphonates

Some 1,3-dithiadiphosphetane 2,4-disulfides (X₂P₂S₄, X: Fc, FcLR; X: CH₃O?C₆H₄?, LR) were allowed to react with alcohols to obtain dithiophosphonic acids (X(OR)PS₂H). These were converted to the corresponding ammonium salts. The salts were of the structures [Fc(OR)PS₂]^?[NH₄]⁺, R: 3-methyl-1-butyl- for I; 1-phenyl-1-propyl- for II; 3-pentyl- for III; 3-phenyl-1-propyl- for IV and [CH₃O?C₆H₄(OR)PS₂]^?[NH₄]⁺, R: 3-methyl-1-butyl- for V and 1-phenyl-1-propyl- for VI. To the best of our knowledge, all the compounds except V were prepared for the first time.

The compounds synthesized were characterized by elemental analysis, NMR (¹H, ¹³C, ³¹P), MS, FTIR, and Raman spectroscopies. Electrochemical behaviors of I–VI at disposable pencil graphite electrode (PGE) were investigated by using cyclic voltammetry (CV) and square-wave voltammetry (SWV). Adsorption and diffusion patterns of all the compounds on the PGE were also studied.

Two electroactive groups were identified in the compounds I–IV and only one in V and VI. The ferrocenyl groups of I-IV were oxidized at around 0.4 V. The same compounds display a second, more intense CV band at 0.8 V. The corresponding band for the compounds V–VI appears at around 0.6 V with a much weaker intensity. It is suggested that the ferrocenyl group introduced into the structures stabilizes the radical species formed as the product of the oxidation of the dithiophosphonato group.     

Synthesis of pyrazoles via electrophilic cyclization

Electrophilic cyclizations of α,β-alkynic hydrazones by molecular iodine were investigated for the synthesis of 4-iodopyrazoles. α,β-Alkynic hydrazones were readily prepared by the reactions of hydrazines with propargyl aldehydes and ketones. When treated with molecular iodine in the presence of sodium bicarbonate, α,β-alkynic hydrazones underwent electrophilic cyclization to afford 4-iodopyrazoles in good to high yields. Iodocyclization was general for a wide range of α,β-alkynic hydrazones and tolerated the presence of aliphatic, aromatic, heteroaromatic, and ferrocenyl moieties with electron-withdrawing and electron-donating substituents.     

Butylene linked palladium N-heterocyclic carbene complexes: Synthesis and catalytic properties

New bis(NHC)-Pd complexes were synthesized and characterized by elemental analysis, ¹H NMR, ¹³C NMR, and IR spectroscopy. The reaction of Pd(OAc)₂ and bis(benzimidazolium) salts in DMSO gave the monomeric palladium complex in which the N-heterocyclic carbene was bound to the metal centre. The crystal and molecular structure of the cis-dibromo{1,1′-di[2,3,4,5,6-pentamethylbenzyl]-3,3′-butylenedibenzimidazol-2,2′-diylidene}-palladium(II) complex was determined by single-crystal X-ray diffraction. The activity of the Pd(II) complexes in the direct arylation of benzothiazole with arylbromides was investigated. A preliminary catalytic study showed that these bis(NHC)-Pd complexes were highly active in the direct arylation of benzothiazole with arylbromides.     

A theoretical investigation of the low energy conformers of the isomers glycine and methylcarbamic acid and their role in the interstellar medium

We have theoretically investigated the low energy conformers of neutral glycine (NH(2)CH(2)COOH) and its isomer methylcarbamic acid (CH(3)NHCOOH) in the gas phase. A total of 16 different levels of the theory, including CCSD(T), MP2 and B3LYP methods with various Pople and Dunning type basis sets with and without polarization and diffuse functions were used. We found eight low energy glycine conformers, where the heavy atoms in three have a planar backbone, and four low energy methylcarbamic acid conformers all with non-planar backbones. Interestingly at all levels of theory, we found that the most stable methylcarbamic acid conformer is significantly lower in energy than the lowest energy glycine conformer. The MP2 level and single point CCSD(T) calculations show the lowest energy methylcarbamic acid conformer to be between 31 to 37 kJ mol(-1) lower in energy than the lowest energy glycine conformer. These calculations suggest that methylcarbamic acid might serve as a precursor to glycine formation in the Interstellar Medium (ISM). We also report the theoretical harmonic vibrational frequencies, infrared intensities, moment of inertia, rotational constants and dipole moments for all of the conformers. In order to understand how glycine or methylcarbamic acid might be formed in the ISM, larger calculations which model glycine or its isomer interacting with several surrounding molecules, such as water, are needed. We demonstrate that B3LYP method should provide a reliable and computationally practical approach to modeling these larger systems.     

Broadband-cascaded four-wave mixing in a photonic crystal fiber around 1 μm

To our knowledge, efficient generation of broadband four-wave mixing cascades centered at 1 μm and spanning 600 nm is experimentally demonstrated for the first time. This frequency comb is generated from a two-tone seed with a maximum peak power of 25 W in a low-dispersion photonic crystal fiber. It consists of up to 44 new idler waves generated symmetrically around the seed.     

Non-linear vibrations of a simple-simple beam with a non-ideal support in between

A simply supported Euler-Bernoulli beam with an intermediate support is considered. Non-linear terms due to immovable end conditions leading to stretching of the beam are included in the equations of motion. The concept of non-ideal boundary conditions is applied to the beam problem. In accordance, the intermediate support is assumed to allow small deflections. An approximate analytical solution of the problem is found using the method of multiple scales, a perturbation technique. Ideal and non-ideal frequencies as well as frequency-response curves are contrasted.