Efficient conversion of substituted aryl thioureas to 2-aminobenzothiazoles using benzyltrimethylammonium tribromide

The reaction of molecular bromine (Br2) with arylthioureas is known to produce 2-aminobenzothiazoles (Hugerschoff reaction). We show here that benzyltrimethylammonium tribromide (1, PhCH2NMe3Br3), a stable, crystalline organic ammonium tribromide (OATB), can be readily utilized as an alternative electrophilic bromine source. It is easier to control the stoichiometry of addition with an OATB, which minimizes aromatic bromination caused by excess reagent. We have developed a direct procedure from isothiocyanates and amines using tetrabutylammonium thiocyanate (Bu4NSCN) and PhCH2NMe3Br3 to afford functionalized 2-aminobenzothiazoles.     

Construction of diverse peptide structural architectures via chemoselective peptide ligation

Herein, we report the development of a facile synthetic strategy for constructing diverse peptide structural architectures via chemoselective peptide ligation. The key advancement involved is to utilize the benzofuran moiety as the peptide salicylaldehyde ester surrogate, and Dap–Ser/Lys–Ser dipeptide as the hydroxyl amino functionality, which could be successfully introduced at the side chain of peptides enabling peptide ligation. With this method, the side chain-to-side chain cyclic peptide, branched/bridged peptides, tailed cyclic peptides and multi-cyclic peptides have been designed and successfully synthesized with native peptidic linkages at the ligation sites. This strategy has provided an alternative strategic opportunity for synthetic peptide development. It also serves as an inspiration for the structural design of PPI inhibitors with new modalities.

Methods of introducing peptide salicylaldehyde esters and hydroxyl amine functionality into the peptide side chain have been developed. Diverse peptide structural motifs were constructed via ligation with native amide linkages at the ligation sites.     

Syntheses,Characterization and Crystal Structures of Three Structurally Similar Dinuclear Schiff Base Cadmium(II) Complexes with Bridging Azide or Thiocyanate Ligands

Three novel Schiff base cadmium(II) complexes, derived from the end‐on (μ‐1,1‐N₃) azide or end‐to‐end (μ‐1,3‐NCS) thio cyanate bridges and similar tridentate Schiff base ligands, have been synthesized under similar synthetic procedures and their crystal structures determined by X‐ray diffraction methods. They are the dinuclear double end‐on azide‐bridged [Cd₂(L1)₂(N₃)₂(μ‐1,1‐N₃)₂] ( 1 ), the dinuclear double end‐on azide‐bridged [Cd₂(L2)₂(N₃)₂(μ‐1,1‐N₃)₂] ( 2 ), and the dinuclear double end‐to‐end thiocyanate‐bridged [Cd₂(L3)₂(NCS)₂(μ_1,3‐NCS)₂] ( 3 ), where L1, L2 and L3 are three similar tridentate Schiff bases obtained by condensation of 2‐pyridylaldehyde with N,N‐diethylethane‐1,2‐diamine, of 2‐pyridylaldehyde with N‐isopropylethane‐1,2‐diamine, and of 2‐pyridylaldehyde with N,N‐dimethylpropane‐1,3‐diamine, respectively. Each cadmium(II) centre in the complexes is in a distorted octahedral coordination. There is a crystallographic inversion centre in each of the complexes. The similar small ligands used as the secondary ligands in the preparation of the cadmium(II) complexes with similar Schiff bases can result in similar structures.     

Structures, relative stability and dissociation of [Si,N,C,O]2+ isomers

Fifteen isomers of [Si,N,C,O]²⁺ system are obtained at UB3LYP/6-311G(d) and UCCSD(T)/6-311+G(2df) (single-point) levels. The analyses are made for predicting the structures of optimized isomers, while ionic fragments with lower energies are suggested. The calculated results indicate that linear isomer SiNCO²⁺(²Π) is thermodynamically the most stable species in [Si,N,C,O]²⁺ system, followed by linear SiOCN²⁺ (²Π), SiCNO²⁺ (²Π), and SiC(NO) (²A) with NCO three-membered ring. The order of stability of several kinetically stable isomers is SiNCO²> SiCNO²⁺ (²Π)>SiOCN²⁺>SiC(NO)²⁺>OSiNC²⁺ (²Π). The obtained results by analyzing the isomerizations and ionic fragment patterns show that the signal peaks of [Si,N,C,O]²⁺ are attributed to the contribution of linear SiNCO²⁺ species, which is metastable and can dissociate to the ionic fragments in the mass spectrometry experiments.     

化学计量一级站量值传递工作及经验

介绍了国防科工委化学计量一级站为保证化学量值的准确与统一,在计量标准建立、标准物质研制、测量方法研究等方面所做的工作和经验。     

Tricarbonyl(dialkylamidocyclohexa-1,3-diene)iron: Preparation,Isomerization and Stereochemistry

The direct reaction of iron pentacarbonyl with diethylamidocyclohexadiene gave three isomeric tricarbonyliron complexes, 1, 2 and 3. Only 1 isomerized to give 2 under acidic conditions, whereas 3 remained unchanged. The chemical properties of the tricarbonyl(amidocyclohexadiene)iron complexes differed from those of the tricarbonyl(carboxycyclohexadiene)iron complexes. Complex 3 which underwent no hydride abstraction with triphenylmethyl hexafluorophosphate, has an exo stereochemistry.     

Interlayer Energy Transfer from Naphthalene to Anthracene Chromophores Organized in Langmuir—Blodgett Films

Interlayer energy transfer between 2,3-naphthol-10-hexadecylaza-15-crown-5(NC16) and N-[1-(9-methoxyanthryl)] decylaza-15-crown-5(A10C) within multilayer Langmuir-Blodgett films has been studied by steady-state fluorescence spectra. The donor and acceptor could be separated precisely by inserting stearic acid (SA) spacers. The efficiency of the energy transfer increases with the decrease in the donor-acceptor distance by a quadratic manner, suggesting the donor excitations are delocalized in the layer.     

Synthesis and Characterization of (βDiketonate)(7-norbornadienyl acetate)Copper(l) Complexes,Single-Crystal Structure of (hfac)Cu(7-AcO-NBD)

Copper(I) complexes of general formula (β-diketonate)Cu(7-AcO-NBD), where 7-AcO-NBD = 7-norbornadienyl acetate and β-diketonate = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate (1), 1,1,1-trifluoro-2,4-pentanedionate (2), 2,4-pentanedionate (3), 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionate (4), 4,4,4-trifluoro-1-phenyl-1,3-butanedionate (5), were prepared from reactions of CuCl with Na(β-diketonate) in the presence of 7-AcO-NBD. AH compounds were characterized by elemental analyses, ¹H, ¹³C, ¹⁹F NMR and IR spectra. Single-crystal strucutre of compound 1 was determined by X-ray diffraction analysis that showed a mononuclear copper species with coordination of a chelating β-diketonate ligand through two oxygen atoms and the 7-AcO-NBD through its C? C double bond and an oxygen atom in the solid state. For compound 1, the crystal data are: triclinic, space group $ {\rm P}\bar 1 $, a= 5.4519(14) Å, b= 11.852(3) Å, c= 13.304(3) Å, α = 74.721(20)° β = 80.220(20)°, γ= 76.848(19)°, Z = 2, R_F = 0.060 and R_w = 0.064. Hot-wall chemical vapor deposition experiments revealed that compound 1 is suitable as a precursor for deposition of copper films in the temperature range 170–260 °C.     

Palladium complexes with ethylene-bridged bis(N-heterocyclic carbene) for C-C coupling reactions

A series of new ethylene-bridged bis(imidazolium) halides with various N-substitutions were synthesized. Complexation of these imidazolium halides with Pd(OAc)₂ produced new Pd(II) ethylene-bridged bis(carbene) complexes. Crystallographic analyses of some of the new imidazolium salts and Pd(II) complexes were determined. Applications of these seven-member palladacycles in Suzuki and Heck coupling reactions produced comparable catalytic activities to those of six-member analogs.