Total synthesis of maremycins A,B, C1/C2, D1, and D2

The total synthesis of maremycins A, B, C₁/C₂, D₁, and D₂ is achieved starting from the natural amino acids l-isoleucine and S-methyl-l-cysteine, in which the total synthesis of maremycins B, C₁/C₂, and D₂ is accomplished for the first time. The synthesis features a position-selective intramolecular bromination process for the synthesis of key chiral building block, a Pd-catalyzed indole synthesis for the preparation of (2S,3S)-β-methyltryptophan and hydroxylation of oxindoles by molecular oxygen. In addition, the protocol for conversion of maremycins A and B to maremycins C and D was improved.     

1,9-Bis(N,N-dimethylaminomethyl)dipyrromethanes in the synthesis of porphyrins bearing one or two meso substituents

A synthesis of 5,15-disubstituted zinc-porphyrins has been developed that employs condensation of a 1,9-bis(N,N-dimethylaminomethyl)dipyrromethane+a dipyrromethane in refluxing ethanol containing zinc acetate followed by oxidation with DDQ. The N,N-dimethylaminomethylation of the dipyrromethane was achieved via Eschenmoser's reagent (N,N-dimethylmethyleneammonium iodide) in CH₂Cl₂ at room temperature. The synthesis is compatible with diverse substituents (e.g., alkyl, aryl, ester, acetal) and enables rapid synthesis of trans-AB-, A₂-, and A-porphyrins. The synthesis of >40 zinc porphyrins has been surveyed; 13 zinc porphyrins were isolated in yields of 5-20% without detectable scrambling.     

Formation of LiAlyNi1−yO2 solid solutions under high and atmospheric pressure

Three methods were used for the synthesis of LiAl_yNi_1−yO₂ solid solutions with layered crystal structure: citrate and hydroxide precursor methods at atmospheric pressure and high-pressure synthesis in oxygen-rich atmosphere (3 GPa). Structural characterization of the oxides was performed by powder XRD analysis and electron paramagnetic resonance (EPR) spectroscopy. Irrespective of the different preparation techniques used, it was found that LiAl_yNi_1−yO₂ solid solutions can be formed in the limited concentration range of 0?y?0.5 and 0.75?y?1.0. The unit cell parameter a decreases linearly with the Al content whereas the unit cell parameter c increases sharper as compared to the linear interpolation of the c parameter calculated for the two end compositions LiNiO₂ and LiAlO₂. In these compositions, aluminum substitutes for Ni in the NiO₂-layer, the mean Al_yNi_1−y-O bond length decreasing. The extent of the trigonal distortion of Al_yNi_1−yO₆ and LiO₆-octahedra varies with the aluminum content and depends on the synthesis procedure used. The LiO₆-octahedra are more flexible to tolerate the increased trigonal distortion as compared to the Al_yNi_1−yO₆-octahedra. High-pressure synthesis favors the formation of oxides with a higher extent of trigonal distortion of both Al_yNi_1−yO₆ and LiO₆-octahedra. From EPR measurements, it was shown that local cationic distribution in LiAl_yNi_1−yO₂ depends on the synthesis temperature. At atmospheric pressure, higher synthesis temperatures promote the reaction of cation mixing between the layers.     

Exploiting morph-DAST mediated ring-expansion of substituted cyclic β-amino alcohols for the preparation of cyclic fluorinated amino acids. Synthesis of 5-fluoromethylproline and 5-fluoropipecolic acid

The synthesis of proline analogues bearing a fluorine-containing substituent at the fifth position of the pyrrolidine ring, racemic trans- and cis-5-fluoromethyl prolines, was performed. The key step of the synthesis is a transformation of the CH₂OH-group into the CH₂F-one using morpholinosulfur trifluoride. During the synthesis, an efficient procedure to prepare trans- and cis-5-fluoropipecolic acids was elaborated.     

Olefin metathesis polymerization: Some recent developments in the precise polymerizations for synthesis of advanced materials (by ROMP,ADMET)

Recent results for synthesis of end-functionalized polymers (EFP) by using olefin metathesis polymerization have been introduced including basic characteristics in ring-opening metathesis polymerization (ROMP) of cyclic olefins and acyclic diene metathesis (ADMET) polymerization for synthesis of conjugated polymers. Several approaches were demonstrated for synthesis of EFP by living ROMP using molybdenum (exclusive coupling with aldehyde) and ruthenium catalysts (sacrificial ROMP, chain transfer). Cis specific (Z selective) ROMPs were achieved by molybdenum, ruthenium, and vanadium catalysts by the ligand modification. The catalytic synthesis of EFP with high cis selectivity has been achieved by combined ROMP with chain transfer by V(CHSiMe₃)(N-2,6-Cl₂C₆H₃)[OC(CF₃)₃](PMe₃)₂. The ADMET polymerization using molybdenum and ruthenium catalysts afforded defect-free, high molecular weight poly(arylene vinylene)s containing all trans olefinic double bonds. The methods for precise synthesis of EFPs, exhibiting unique optical properties combined with the end groups, were developed. The catalytic one-pot syntheses for EFPs have also been developed.     

A type 2 Ferrier rearrangement-based synthesis of d-myo-inositol 1,4,5-trisphosphate

The synthesis of d-myo-inositol 1,4,5-trisphosphate (InsP₃) from methyl α-d-glucopyranose, via a type 2 Ferrier rearrangement is reported. A key intermediate in this synthesis possesses orthogonal protecting groups at the 1-, 4- and 5-position, making it a versatile starting point for the synthesis of unnatural InsP₃ derivatives. Biological evaluation of the synthetic InsP₃ demonstrates that this compound evokes selective Ca²⁺ release via activation of InsP₃ receptors.     

Iron-catalyzed hydroaminocarbonylation of alkynes: Selective and efficient synthesis of primary α,β-unsaturated amides

α,β-Unsaturated primary amides are important intermediates and building blocks in organic synthesis. Herein, we report a ligand-free iron-catalyzed hydroaminocarbonylation of alkynes using NH₄HCO₃ as the ammonia source, enabling the highly efficient and regioselective synthesis of linear α,β-unsaturated primary amides. Various aromatic and aliphatic alkynes are transformed into the desired linear α,β-unsaturated primary amides in good to excellent yields. Further studies show that using NH₄HCO₃ as the ammonia source is key to obtain good yields and selectivity. The utility of this route is demonstrated with the synthesis of linear α,β-unsaturated amides including vanilloid receptor-1 antagonist TRPV-1.     

Catalytic transformations of sulfur dioxide into organic sulfur compounds

The applications of catalytic transformations of SO₂ into sulfur-containing organic compounds, reported in the literature, are briefly reviewed. The authors' studies in this field of chemistry,viz., the hydrosulfination of alkenes, the synthesis of γ-oxo sulfonesvia hydrosulfination, and the synthesis of aromatic sulfinic acids from diazonium salts, are summarized. Current results on the synthesis of the new sulfinato complex [Pd(SO₂Ph)(Cl)dppp] and its hydrogenation to PhSO₂H are presented, and a mechanism for the catalytic synthesis of sulfinic acids is proposed. The structure of ([Pd(μ-Cl)(dppp)l₂ ²⁺(SO₄)^2?·4SO₂ salt is studied by X-ray diffraction analysis.     

Synthesis of meso-tetraarylporphyrins using SeO2 as oxidant

The oxidative step of the two-step, one-flask synthesis of meso-tetraarylporphyrins is herein conducted with heterogeneous oxidant SeO₂ instead of the usual quinones DDQ or p-chloranil. Evaluation of BF₃O(Et)₂ or I₂ amount for the condensation of the first step combined with the excess of SeO₂ defined porphyrin synthesis conditions employing benzaldehydes and pyrrole (or 5-phenyldipyrromethane) as starting materials. The simplicity of the workup, allied with reaction mild conditions, makes this method a good option for the synthesis of this kind of compound.     

A green route for microwave synthesis of sodium tungsten bronzes NaxWO3 (0<x<1)

A green route has been developed for microwave synthesis of sodium tungsten bronzes Na_xWO₃ (0<x<1) from Na₂WO₄, WO₃ and tungsten powder. The hybrid microwave synthesis was carried out in argon atmosphere using CuO powder as the heating medium. Tungsten powder is used as the reducing agent instead of the alkali metal iodides previously used for the microwave synthesis of oxide bronzes. The prepared samples were characterized by powder X-ray diffraction, energy-dispersive X-ray analysis and scanning electron microscopy, and their phase constitutions, crystal structures and morphologies are in consistence with that in the literature. This synthesis method is simple, green and atom economic, and promising for preparation of other oxide bronzes and related compounds.     

d- and l-Serine, useful synthons for the synthesis of 24-hydroxyvitamin D3 metabolites. A formal synthesis of 1α,24R,25-(OH)3-D3, 24R,25-(OH)2-D3 and 24S,25-(OH)2-D3

d- and l-Serine have been used for the enantioselective synthesis of tosylates 7a and 7b, useful building blocks for the synthesis of triols 5a and 5b which have already been obtained via a diastereoselective synthesis and used for the synthesis of 2a, 2b and 2c. We have thus performed a formal synthesis of 24S,25-(OH)₂-D₃, 24R,25-(OH)₂-D₃ and 1α,24R,25-(OH)₃-D₃.     

Boron trifluoride etherate-assisted ring opening of ethylene oxide by a chiral organolithium: enantioselective synthesis of (R)-N-Boc-2-(2-hydroxyethyl)pyrrolidine

A practical synthesis of (R)-N-Boc-2-(2-hydroxyethyl)pyrrolidine in high enantiomeric purity is described. The synthesis involves BF₃·Et₂O-assisted ring opening of ethylene oxide by a homochiral carbanion (R)-3, which is derived from sparteine-mediated asymmetric deprotonative lithiation of 1-Boc-pyrrolidine.     

Atropo-enantioselective synthesis of a C3-symmetric tripodal ligand with three axially chiral biaryl subunits

In contrast to the numerous successful applications of C₂-symmetric biaryls as powerful tools for asymmetric synthesis, there have so far been only few reports on combinations of C₃-symmetry with axial chirality. We present here the first enantioselective synthesis of a novel family of tripodal ligands containing three axially chiral biaryl subunits in an (M,M,M)- or, optionally, (P,P,P)-configured form. The incorporation of a PCl₂- and a TiCl-fragment into the central cavity was achieved.     

Synthesis of ceria nanosheets on the surface of Ce(NO3)3 solution by interaction with gaseous ammonia

The surfactant-free synthesis of a solid film of ceria was carried out at the air–water interface from an aqueous solution of Ce(NO₃)₃ and gaseous NH₃ as reactants. The synthesized CeO_2?x ? n H₂O film consists of 2D nanocrystals with a fluorite structure. The film can form a planar coating on the surface of a solid substrate or transform into curved fragments upon drying, depending on the synthesis conditions.     

Effect of nanoparticles agglomeration on electrical properties of La1−xAxMnO3 (A = Sr,Ba) nanopowder and ceramic solid solutions

Peculiar features of the sol–gel synthesis of substituted manganites La_1−xA_xMnO₃ (A = Sr, Ba) have been investigated. Variation of the gel pH during synthesis was shown to affect the aggregation of particles and their crystal structure. Electrical properties of nanopowder and ceramic La_1−xA_xMnO₃ solid solutions were studied. Additional heat treatment was revealed to affect not only the resistivity, but also the character of its temperature dependence. It was shown that under the synthesis and heat treatment conditions used in the work, the La_1−xBa_xMnO₃ solid solutions with x = 0.15 have the lowest conductivity at 1200 K, which allows using them as thick-film cathodes.     

A facile one-pot synthesis of 2-fluoroalkyl 1,3-imidazolines and 1,3-oxazolines through imidoyl halide intermediates

A facile one-pot procedure has been developed for the synthesis of 1,3-imidazolines and 1,3-oxazolines bearing fluorinated alkyl groups at the 2-position. The reaction involves the condensation of N-monosubstituted ethane-1,2-diamines or 2-aminoethanols with a fluorinated carboxylic acid in the presence of PPh₃/CX₄. The proposed mechanism is that the amide intermediates were initially formed, and then converted to the imidoyl halide intermediates in the presence of PPh₃/CX₄, followed by rapid intramolecular cyclization to 1,3-diazoline products. This protocol allows for the synthesis of 2-bromodifluoromethyl-1,3-imidazoline, a useful CF₂Br-heterocyclic building block, which can be used for the synthesis of gem-difluoromethylene linked compounds.     

An efficient and mild oxidant for the synthesis of s-tetrazines

PhI(OAc)₂ serves as a mild and effective oxidant for the synthesis of s-tetrazine derivatives—molecules of emerging significance to the field of bioorthogonal chemistry. This reagent serves as a complementary oxidant to harsher nitrous reagents. The use of PhI(OAc)₂ improves the synthesis of 5-amino-di(pyridin-2-yl)-s-tetrazine, a molecule that has been broadly used for cellular imaging and nuclear medicine. The generality of PhI(OAc)₂ as the oxidant for tetrazine synthesis is demonstrated for nine tetrazines in 75–98% yield.     

A simple, novel and convenient method for the synthesis of 1-aminophosphinic acids: synthesis of a novel C2-symmetric phosphinic acid pseudodipeptide

A simple, efficient and novel method has been developed for the synthesis of 1-aminophosphinic acids from simple starting materials. Treatment of aromatic aldehydes with ammonia and hypophosphorus acid gives novel C₂-symmetric 1-aminoarylmethylphosphinic acids. The synthesis of novel C₂-symmetric phosphinic acid pseudodipeptides is also discussed.     

Novel route in the synthesis of ψ[CH2NH] amide bond surrogate

An alternative method for the synthesis of pseudopeptides containing a ψ[CH₂NH] amide bond surrogate is reported. The synthetic approach is based on a nucleophilic displacement of the chiral N-protected β-iodoamines with conveniently protected amino acid esters. The compatibility of this method with both conventional and microwave-assisted peptide synthesis should increase the potentiality of the ψ[CH₂NH] peptide bond isostere in peptide chemistry.     

Synthesis of Complex Tungsten-Zirconium Carbonitrides

The process parameters (temperature, atmosphere, and composition) of the synthesis of complex carbonitrides W_1?xZr _x C_1?yN _y were determined. The area of formation of homogeneous carbonitrides in synthesis from refractory compounds and from WC and zirconium oxide was found. The conditions of appearance of the hemicarbide W₂C were elucidated. The possibility of fabricating homogeneous carbonitrides (CNs) at the lower temperature of the synthesis by increasing fineness of the starting components by vibrogrinding was examined.