Biomimetic synthesis of acid-sensitive (-)-caparrapi oxide and (+)-8-epicaparrapi oxide induced by artificial cyclases

[reaction: see text] Asymmetric total syntheses of acid-sensitive (-)-caparrapi oxide (1) and (+)-8-epicaparrapi oxide (2) from farnesol (9) were achieved using Sharpless-Katsuki epoxidation and Lewis acid-assisted chiral Bronsted acid (chiral LBA)-induced polyene cyclization as key steps. Furthermore, (-)-1 could be directly synthesized from (S)-nerolidol (3) and (R)-LBA with 88% ds by reagent control which overcame substrate control, while (-)-2 was obtained from (R)-3 and (R)-LBA with >99% ds by the double-asymmetric induction.     

An activated scheme for resonance energy transfer in conjugated materials

Energy transfer mechanism in conjugated materials has been demonstrated with an activated expression, which is equivalent to Fermi's golden rule. Spectral overlap integrals obtained from simulated spectra of model chromophores agree very well with the results obtained with the activated formula. Although this approach works best for chromophores with spectral profiles resembling a Gaussian distribution, the activated expression formula also performs quite well for chromophores with vibronically resolved spectra. Activation energies for exciton hopping can also be predicted using a phonon coupled exciton relaxation scheme. The accuracy of predictions with this new approach is quite attractive and hence should allow practical applications.     

A computational method for large‐scale differential symmetric Stein equation

We propose a numerical method for solving large‐scale differential symmetric Stein equations having low‐rank right constant term. Our approach is based on projection the given problem onto a Krylov subspace then solving the low dimensional matrix problem by using an integration method, and the original problem solution is built by using obtained low‐rank approximate solution. Using the extended block Arnoldi process and backward differentiation formula (BDF), we give statements of the approximate solution and corresponding residual. Some numerical results are given to show the efficiency of the proposed method.     

Base Mediated Aromatization of Carbonyl Condensation Products Derived from 2‐(2‐Bromoprop‐2‐enyl)cyclohexanone Derivatives via ‘Intramolecular Unsaturation Transfer’

Alkylbenzenes are synthesized for the first time from aliphatic hydrocarbons via an one pot, transition metal‐free coupling approach under basic conditions. The method consists of two steps: condensation of 2‐bromoprop‐2‐enyl‐ or 2‐propargylcyclohexanone with alcohols, amines, or amino alcohols, followed by base treatment (Scheme 1). Phenolic ethers and N‐phenylated polyalkyl aromatic compounds are shown to be in the scope of the demonstrated reaction (Table). The proposed mechanism suggests that the unsaturation in another part of the molecule (propargyl‐group equivalent) is transferred into the cyclohexane ring to yield a benzene ring through a series of prototropic shifts.     

Synthesis,characterization and non-linear optical properties of two mononuclear Cu(II) complexes of 2,6-bis(1-butylbenzimidazol-2-yl)pyridine

Two copper(II) complexes, [Cu(L)(N₃)₂]·MeOH and [Cu(L)(NCS)₂]·MeOH, were prepared and characterized by spectroscopic, analytical, and quantum chemical studies, where L is 2,6-bis(1-butylbenzimidazol-2-yl)pyridine. X-ray quality crystals of [Cu(L)(N₃)₂]·MeOH were obtained by slow evaporation of MeOH solution of the complex. Molecular structure of [Cu(L)(N₃)₂]·MeOH was determined by X-ray crystallography. The asymmetric unit contains one [Cu(L)(N₃)₂] and one MeOH molecule. Cu(II) in [Cu(L)(N₃)₂]·MeOH is five-coordinate, bonded to five nitrogens (three from L and two from two azide anions). Coordination geometry around Cu(II) center is distorted square-pyramidal with τ value of 0.065. Optimized geometries, IR spectra, and non-linear optical properties of the complexes were obtained by computational studies based on density functional theory (DFT) with M062X method. NLO properties of these complexes were investigated computationally and both complexes exhibit better NLO properties than urea.     

Synthesis,crystal structure,thermal decomposition,and XPS studies of homo and heterotrinuclear Cu(II)–Cu(II)–Cu(II) and Cu(II)–Ni(II)–Cu(II) complexes obtained from salpn type ligands

In this study, a mononuclear CuL complex was prepared by the use of bis-N,N′-(salicylidene)-1, 3-propanediamine (LH₂) and Cu²⁺ ion. NiCl₂ and NiBr₂ salt were treated with this complex in dioxanewater medium and two new complexes [(CuL)₂NiCl₂(H₂O)₂] and [(CuL)₂NiBr₂(H₂O)₂)] with Cu(II)–Ni(II)–Cu(II) nucleus structure were obtained. In addition to this bis-N,N′-(2-hydroxybenzyl)-1,3-diaminopropane (L^HH₂) was prepared by the reduction of LH₂ with NaBH₄ in MeOH medium. The treatment of this reduced complex with Cu²⁺ ion resulted a complex [(CuL^H)₂CuCl₂] with a structure of Cu(II)–Cu(II)–Cu(II). The complexes prepared were characterized by the use of elemental analysis, IR spectroscopy, thermogravimetric and X-ray diffraction methods. The crystal structures of [(CuL)₂NiBr₂(H₂O)₂] (СIF file CCDC 1448402) and [(CuL^H)₂CuCl₂] (СIF file CCDC 1448401) complexes were elucidated. It was found that halogen ions are coordinated to terminal Cu²⁺ ions which are in a distorted square pyramid coordination sphere. It was determined that the central Cu(II), which joins terminal square pyramidal Cu(II), was coordinated only by the phenolic oxygens of the ligand while the central Ni(II) was coordinated by two phenolic oxygens of the organic ligand and two water molecules. These complexes were investigated by XPS and it was found that the terminal and central Cu²⁺ ions were different in Cu(II)–Cu(II)–Cu(II) complex. Also, the thermal degradation of the CuLH complex unit was observed to exothermic in contrast to the expectations.

     

Chemo- and Enantioselective Oxidative α-Azidation of Carbonyl Compounds

We report high-performance I⁺/H₂O₂ catalysis for the oxidative or decarboxylative oxidative α-azidation of carbonyl compounds by using sodium azide under biphasic neutral phase-transfer conditions. To induce higher reactivity especially for the α-azidation of 1,3-dicarbonyl compounds, we designed a structurally compact isoindoline-derived quaternary ammonium iodide catalyst bearing electron-withdrawing groups. The nonproductive decomposition pathways of I⁺/H₂O₂ catalysis could be suppressed by the use of a catalytic amount of a radical-trapping agent. This oxidative coupling tolerates a variety of functional groups and could be readily applied to the late-stage α-azidation of structurally diverse complex molecules. Moreover, we achieved the enantioselective α-azidation of 1,3-dicarbonyl compounds as the first successful example of enantioselective intermolecular oxidative coupling with a chiral hypoiodite catalyst.