The curious case of a sterically crowded Stenhouse salt

We report a peculiar Stenhouse salt. It does not evolve into cyclopentenones upon basification, due to the steric hindrance of its bulky stable carbene patterns. This allowed for the observation and characterization of the transient open-chain neutral derivative, which was isolated as its cyclized form. The latter features an unusually long reactive C–O bond (150 pm) and a rich electrochemistry, including oxidation into an air-persistent radical cation.

Bulky substituents of a Stenhouse salt prevent the usual formation of a cyclopentenone upon deprotonation. For the first time, a transient open-chain neutral derivative was observed; the cyclized form and an air-persistent radical were isolated.     

Larix Sibirica Arabinogalactan Hydrolysis over Zr-SBA-15; Depolymerization Insight

Arabinogalactan depolymerization over solid Zr-containing SBA-15-based catalyst was studied via HPLC, GPC, and theoretical modeling. Arabinogalactans (AG) are hemicelluloses mainly present in larch wood species, which can be extracted on an industrial scale. The application of solid acid catalysts in the processes of hemicellulose conversion can exclude serious drawbacks such as equipment corrosion, etc. Characterization of 5%Zr-SBA-15 confirmed the successful formation of the mesoporous structure inherent to SBA-15 with fine Zr distribution and strong acidic properties (XRD, XPS, FTIR, pH_pzc). Carrying out the process at 130 °C allowed us to achieve total products yield of up to 59 wt%, which is represented mainly by galactose (51 wt%) and minor (less than 9 wt%) presence of arabinose, furfural, 5-HMF, and levulinic acid. The temperature increases up to 150 °C resulted in a total product yield drop down to 37 wt%, making temperature elevation above 130 °C obsolete. According to the theoretical investigations, arabinogalactan depolymerization follows the primary cleavage of the β(1→3) bonds between the D-galactose units of the main chain, which is also confirmed by GPC.     

Thermal behavior of oligo[(ε-caprolactone)-co-δ-gluconolactone] enzymatically synthesized in reaction conditions optimized by experimental design

Journal of Thermal Analysis and Calorimetry - The thermal behavior of co-oligomers of ε-caprolactone (ECL) with gluconolactone, compared to the ε-caprolactone oligomer, has been assessed...     

Hybrides of Alkaloid Lappaconitine with Pyrimidine Motif on the Anthranilic Acid Moiety: Design,Synthesis, and Investigation of Antinociceptive Potency

Convenient and efficient routes to construct hybrid molecules containing diterpene alkaloid lappaconitine and pyrimidine fragments are reported. One route takes place via first converting of lappaconitine to 1-ethynyl-lappaconitine, followed by the Sonogashira cross-coupling-cyclocondensation sequences. The other involves the palladium-catalyzed carbonylative Sonogashira reaction of 5′-iodolappaconitine with aryl acetylene and Mo (CO)₆ as the CO source in acetonitrile and subsequent cyclocondensation reaction of the generated alkynone with amidines. The reaction proceeded cleanly in the presence of the PdCl₂-(1-Ad)₂PBn∙HBr catalytic system. The protocol provides mild reaction conditions, high yields, and high atom and step-economy. Pharmacological screening of lappaconitine-pyrimidine hybrids for antinociceptive activity in vivo revealed that these compounds possessed high activity in experimental pain models, which was dependent on the nature of the substituent in the 2 and 6 positions of the pyrimidine nucleus. Docking studies were undertaken to gain insight into the possible binding mode of these compounds with the voltage-gated sodium channel 1.7. The moderate toxicity of the leading compound 12 (50% lethal dose (LD₅₀) value was more than 600 mg/kg in vivo) and cytotoxicity to cancer cell lines in vitro encouraged the further design of therapeutically relevant analogues based on this novel type of lappaconitine–pyrimidine hybrids.     

Features of two- and multicomponent heterocyclization reactions involving 3,4-disubstituted 5-aminopyrazoles and alkyl pyruvates

Three-component heterocyclizations of pyruvic acids and their esters with 5-aminopyrazoles and aromatic aldehydes, in addition to the sequential versions of these reactions, under different activating conditions were studied. Under conventional heating, pyrazolopyrimidine derivatives containing a hydroxyl group in the 6-position were formed in both two- and three-component treatments. Whereas the application of an inert atmosphere did not influence the outcome of these reactions, the use of ultrasonic irradiation led to the formation of 7-hydroxy-tetrahydropyrazolopyrimidines in multi-component reactions and 6-hydroxy-dihydropyrazolopyrimidines in the case of a step-by-step approach. The products of the latter treatment were further transformed into heteroaromatized 6-hydroxy-pyrazolopyrimidines by conventional heating.     

Stereochemistry and tautomerism of silicon-containing 1,2,3-triazole: ab initio and NMR study

Structural Chemistry - In this paper, an approach is proposed for determining the ratio of prototropic annular tautomers of organosilicon 1,2,3-triazoles, which are hardly experimentally determined...     

Towards the Molecular Design of Spin-Crossover Complexes of 2,6-Bis(pyrazol-3-yl)pyridines

The molecular design of spin-crossover complexes relies on controlling the spin state of a transition metal ion by proper chemical modifications of the ligands. Herein, the first N,N’-disubstituted 2,6-bis(pyrazol-3-yl)pyridines (3-bpp) are reported that, against the common wisdom, induce a spin-crossover in otherwise high-spin iron(II) complexes by increasing the steric demand of a bulky substituent, an ortho-functionalized phenyl group. As N,N’-disubstituted 3-bpp complexes have no pendant NH groups that make their spin state extremely sensitive to the environment, the proposed ligand design, which may be applicable to isomeric 1-bpp or other families of popular bi-, tri- and higher denticity ligands, opens the way for their molecular design as spin-crossover compounds for future breakthrough applications.     

Alkylthio(4-methylpent-3-en-1-ynyl)carbenes: generation by the photolysis of 5-alkylthioethynyl-3,3-dimethyl-3H-pyrazoles and reactions with alkenes

1. Download high-res image (56KB)
2. Download full-size image

     

Trinuclear Cyanido-Bridged [Cr2Fe] Complexes: To Be or not to Be a Single-Molecule Magnet,a Matter of Straightness

Trinuclear systems of formula [{Cr(L^N3O2Ph)(CN)₂}₂M(H₂L^N3O2R)] (M=Mn^II and Fe^II, L^N3O2R stands for pentadentate ligands) were prepared in order to assess the influence of the bending of the apical M−N≡C linkages on the magnetic anisotropy of the Fe^II derivatives and in turn on their Single-Molecule Magnet (SMM) behaviors. The cyanido-bridged [Cr₂M] derivatives were obtained by assembling trans-dicyanido Cr^III complex [Cr(L^N3O2Ph)(CN)₂]⁻ and divalent pentagonal bipyramid complexes [M^II(H₂L^N3O2R)]²⁺ with various R substituents (R=NH₂, cyclohexyl, S,S-mandelic) imparting different steric demand to the central moiety of the complexes. A comparative examination of the structural and magnetic properties showed an obvious effect of the deviation from straightness of the M−N≡C alignment on the slow relaxation of the magnetization exhibited by the [Cr₂Fe] complexes. Theoretical calculations have highlighted important effects of the bending of the apical C−N−Fe linkages on both the magnetic anisotropy of the Fe^II center and the exchange interactions with the Cr^III units.