Enantioselective intramolecular amidation of sulfamate esters catalyzed by chiral manganese(III) Schiff-base complexes

Enantioselective intramolecular amidation of sulfamate esters catalyzed by chiral manganese(III) Schiff-base complexes under mild conditions (PhI(OAc)₂, Al₂O₃, C₆H₆, 5 °C) was achieved in moderate to good yields (up to 92%), substrate conversions (up to 99%), with virtually complete cis-selectivity and with ee values up to 79% ee.     

Effect of medium acidity on the efficiency of oxidation of 2,4,6-trinitrotoluene to 2,4,6-trinitrobenzoic acid

An effect of boric acid additives on oxidation of 2,4,6-trinitrotoluene (TNT) to 2,4,6-trinitrobenzoic acid (TNBA) with chromic anhydride in concentrated (96—100%) H₂SO₄ has been studied. In the presence of tetrahydrosulfatoboric acid HB(HSO₄)₄ formed in situ (up to 5 mol.%) or added as a preliminary prepared solution (up to 1 mol. %), TNT is selectively oxidized to TNBA in the yields up to 95—99%. The mechanism including formation of TNT dication as a key step of its oxidation at the methyl group has been suggested.     

Asymmetric synthesis of 2,6-substituted dihydropyrone catalyzed by 3-monosubstituted and 3,3′-bisubstituted BINOL titanium complexes

Asymmetric hetero-Diels-Alder (HDA) reactions of aromatic aldehydes with Danishefsky’s diene derivative were carried out smoothly in the presence of the Ti(IV)-(R)-BINOL (1:1.2) complex to give the corresponding chiral 2,6-disubstituted dihydropyrones under mild conditions. The readily accessible I-Ti(OCH(CH₃)₂)₄ (1.2:1) complex was found to be an effective catalyst for this reaction. Aromatic aldehydes afforded the corresponding products in moderate yields (up to 72 %) with good enantioselectivities (up to 80 % ee). Aromatic aldehydes in presence of the TiCl₄-NaOCH₃-II (1:4.2:1.2) complex gave the products in higher yields (up to 73 %) with better enantioseletivities (up to 84 % ee).     

Oxidation of alcohols with hydrogen peroxide catalyzed by soluble iron and osmium derivatives

Summary Osmium chloride OsCl₃ efficiently catalyzes (yields of products up to 90%, turnover numbers (TON) up to 1500) the oxidation of 2-cyanoethanol with hydrogen peroxide to produce the corresponding aldehyde and acid. Oxidation of isopropanol over OsCl₃ gave acetone in 58% yield. The reactions were carried out either in acetonitrile or without any solvent. The analogous iron compound FeCl₃ was found to be less efficient in the oxidation of 2-cyanoethanol (yields of products up to 67%, TON up to 135). Oxidation of isopropanol in this case gave acetone (yield 53%) and acetic acid (yield 11%). Some other soluble derivatives of iron or osmium exhibited noticeably lower catalytic activity in the alcohol oxidation with H₂O₂.     

Mixing state of amphiphilic di-block copolymer/homopolymer blends

Summary The mixing state of amphiphilic di-block copolymers consisted of poly(ethylene oxide) and poly(methacrylate) having azobenzene moieties in the side chains p(EO)₁₁₄pMA(Az)₂₄ and poly(ethylene oxide) p(EO)₁₁₄ was investigated from the viewpoints of isothermal crystallization and nano-scale ordered structure. The chemical potential, which required establishing the constant crystal growth rate, decreased with the p(EO) content up to 60%. The hexagonal packed cylinder structure was observed for the blends with the p(EO) content up to 60% and the lattice spacing of (100) and (110) planes increased with the p(EO) content up to 60%. The blends of amphiphilic p(EO)₁₁₄pMA(Az)₂₄ and p(EO)₁₁₄ were miscible without in the p(EO) content below 60%.     

Palladium-Catalyzed C-Phenylation of Methyl Acrylate with Triphenylbismuth Dicarboxylates

A new catalytic reaction of C-phenylation of methyl acrylate with bismuth derivatives Ph₃Bi(O₂CR)₂ (R = H, Me, Et, Bu, CF₃, Ph) or Ph₃BiCl₂ in a 3 : 1 ratio was studied. The reaction was performed in the presence of 4 mol % palladium compounds PdCl₂, Pd(OAc)₂, Pd₂(dba)₃, Pd(Ph₃P)₂Cl₂, and PdLCl₂ (L = dppm, dppe, dppp, dppb, dppf, binap, xantphos) at 50°C in CH₃CN, DMF, THF, or CH₂Cl₂ and gave methyl cinnamate (yield up to 85% based on the starting bismuth compound), diphenyl (up to 138%), and benzene (up to 59%).     

Flexible poly(dimethyl siloxane) composites enhanced with 3D porous interconnected three-component nanofiller framework for absorption-dominated electromagnetic shielding

A new poly(dimethyl siloxane) (PDMS) composite was developed based on the 3D porous interconnected framework that is fabricated from reduced graphene oxide (rGO) and Dy₂O₃ decorated single-walled carbon nanotube (Dy₂O₃@SWNT). Despite merely containing ~0.6 wt% fillers, the composite prepared by backfilling 3D framework (3D-Dy₂O₃@SWNT-rGO) with PDMS prepolymer acquires as high as 32.9 dB of absorption-dominated (92.3%–96.9%) electromagnetic interference (EMI) shielding effectiveness in X-band, and up to 47% and 52% increments of respective compressive strength and modulus at 50% strain relative to PDMS. These performances result from the excellent combination of electrical conductivity (up to 0.317 S cm⁻¹), magnetism (up to 7.1 × 10⁻⁵ emu g⁻¹ of susceptibility), and mechanical toughness (complete recovery after 80% compression) in a single three-component filler system of 3D-Dy₂O₃@SWNT-rGO. Moreover, the organic integration of mechanical flexibility of PDMS with shape-tunable ability of 3D-Dy₂O₃@SWNT-rGO enables PDMS composites developed here to EMI-shield any shape surfaces.     

Highly Enantioselective Transfer Hydrogenation of Ketones with Chiral (NH)2P2 Macrocyclic Iron(II) Complexes

Bis(isonitrile) iron(II) complexes bearing a C₂‐symmetric diamino (NH)₂P₂ macrocyclic ligand efficiently catalyze the hydrogenation of polar bonds of a broad scope of substrates (ketones, enones, and imines) in high yield (up to 99.5 %), excellent enantioselectivity (up to 99 % ee), and with low catalyst loading (generally 0.1 mol %). The catalyst can be easily tuned by modifying the substituents of the isonitrile ligand.     

l-Proline derived triamine as a highly stereoselective organocatalyst for asymmetric Michael addition of cyclohexanone to nitroolefins

l-Proline derived triamine 4 has been developed as a highly efficient and stereoselective organocatalyst for the asymmetric Michael addition of cyclohexanone to nitroolefins. In the presence of (CF₃SO₂)₂NH, 4 catalyzed the reaction of cyclohexanone to a variety of nitroolefins with high yields (up to 99%) and excellent diastereoselectivities (up to 99:1 dr) and enantioselectivities (up to 98% ee).     

Copper-catalyzed enantioselective 1,4-conjugate addition of dialkylzinc reagents to α,β- and α,β,γ,δ-unsaturated ketones

An enantioselective Cu(II)-catalyzed conjugate addition of dialkylzinc reagents to α,β- or α,β,γ,δ-unsaturated ketones with chiral cyclohexane-based amidophosphine ligands was developed. With 2 mol% of Cu(OAc)₂·H₂O/L5, the conjugate addition of diethylzinc to α,β-unsaturated ketones was achieved in good-to-excellent yields (up to 98%) and high enantioselectivities (up to 92% ee). This catalytic system was shown to be efficient for the 1,4-conjugate addition of Et₂Zn to (2E,4E)-1,5-diphenylpenta-2,4-dien-1-one with 85% yield and 90% ee. Moreover, with 1 mol% of Cu(OTf)₂/L11, the conjugate addition of α,β,γ,δ-unsaturated ketones was accomplished with 1,4-regioselectivity, good yields (79–86%) and excellent enantioselectivities (up to 97% ee).     

Copper(II)-containing C2-symmetric bistetracarboline amides in enantioselective Henry reactions

A series of new C₂-symmetric chiral diamides were synthesized from l-tryptophan and used as chiral ligands chelated with Cu(II) in enantioselective Henry reactions. Ligand 4a with CuCl₂·2H₂O (5%) showed effective catalytic efficiency in Henry reaction. High yields (up to 99%) and excellent enantioselectivities (up to 98%) were achieved for both aromatic and aliphatic aldehyde substrates.     

Study on the Capabilities of One- and Two-Stage Separation Schemes for Producing Highly Enriched Carbon-13 by the Laser Method

The feasibility of obtaining highly enriched (up to 99.5%) carbon-13 by the method of isotopically selective IR multiple-photon dissociation (MPD) of Freon 22 (CF₂HCl) molecules was studied for one- and two-stage schemes of the process in a laboratory apparatus with the intracavity location of a separation reactor. The concentration of ¹³C in the dissociation product C₂F₄ (tetrafluoroethylene) and the MPD yields were measured depending on the frequency and fluence of laser radiation, as well as on the Freon 22 pressure. At the irradiation geometry used, the concentrations of ¹³C up to 88% were obtained in the first stage of enrichment. The second enrichment stage was based on the isotope-selective dissociation of Freon 22 preliminarily enriched with ¹³C (up to 32.6%). After the second stage, the final ¹³C concentration of 99.5 ± 0.5% was attained in the product C₂F₄.     

C2-Symmetric 4,4′,5,5′-Tetrahydrobi(oxazoles) and 4,4′,5,5′-Tetrahydro-2,2′-methylenebis[oxazoles] as Chiral Ligands for Enantioselective Catalysis Preliminary Communication

The synthesis of a series of enantiomerically pure, C₂-symmetric 4,4′,5,5′-tetrahydro-2,2′-methylenebis[oxazoles] and 4,4′,5,5′-tetrahydro-2,2′-bi(oxazoles) is reported. Copper complexes with anionic tetrahydromethylenebis[oxazole] ligands are efficient catalysts for the enantioselective cyclopropane formation from olefins and diazo compounds (up to 96% ee in the reaction of styrene with menthyl diazoacetate). Tetrahydrobi(oxazole)iridium(I) complexes were found to catalyze transfer hydrogenations of aryl alkyl ketones with i-PrOH (up to 91% ee). Tetrahydrobi(oxazole)palladium complexes can be used as enantioselective catalysts for allylic nucleophilic substitution (up to 77% ee in the reaction of PhCH?CHCH(OAc)Ph with NaHC(COOMe)₂).     

Synthesis of α-chloropolyfluoroalkyl ethers and acetals based on them

α-Chloropolyfluoroalkyl ethers were synthesized by the reaction of polyfluorinated alcohols H(CF₂CF₂) _n CH₂OH (n=1?3) with aliphatic aldehydes (ethanal, propanal, butanal) and hydrogen chloride. Yield of α-chloroethers decreases from 71 to 61% as the number of carbon atoms in the starting reactants increases. α-Chloropolyfluoroalkyl ethers react with polyfluorinated alcohols (n = 1?3) to form acetals in yield of up to 40–61%, and with methanol and ethanol, up to 98%.     

Enantioselective water-soluble iron–porphyrin-catalyzed epoxidation with aqueous hydrogen peroxide and hydroxylation with iodobenzene diacetate

The asymmetric epoxidation of styrene derivatives by H₂O₂ (or UHP) to give optically active epoxides (ee up to 81%) and hydroxylation of alkanes to give optically active secondary alcohols (ee up to 78%) were carried out in methanol and water using chiral water-soluble iron porphyrins as catalysts.     

Enantio- and diastereoselective construction of vicinal quaternary and tertiary carbon centers by catalytic Michael reaction of α-substituted β-keto esters to cyclic enones

A catalytic enantio- and diastereoselective Michael reaction was achieved to construct vicinal quaternary and tertiary carbon centers in one step. Using 5 mol % of La(O-i-Pr)₃ and 10 mol % of a new N-linked-BINOL type ligand, the reaction of α-substituted β-keto esters to cyclic enones provided the corresponding Michael adducts in up to quantitative yield with a diastereomeric ratio up to 86/14 and enantiomeric excess up to 86% for the major isomer. An alternative catalyst preparation method using La(OTf)₃ instead of La(O-i-Pr)₃ was also examined.     

A new Yb-catalyzed pinacol and imine-coupling reaction

Ytterbium triflate, Yb(OTf)₃, catalyzes the intermolecular reductive homocouplings of imines, aldehydes, and ketones at loadings of 5 mol % in the presence of Mg and Me₃SiCl to give isolated yields of up to 95%. Diastereoselectivity of up to 4/96 (dl/meso) is achieved for aromatic aldehydes, up to 100% dl for aliphatic aldehydes, and 100% dl for an intramolecular imine coupling.     

CuII-catalysed asymmetric 1,3-dipolar cycloaddition of azomethine ylides with a chiral ferrocene-derived P,N-ligand

A ferrocene-derived P,N-heterodonor ligand was effectively used in a Cu(OAc)₂·H₂O-catalysed asymmetric 1,3-dipolar cycloaddition of azomethine ylides with maleate derivatives, affording cycloadducts with high yields (up to 96%), diastereoselectivities (>99 dr), and enantioselectivities (up to 99% ee).     

Chiral ligands with pyridine donors in transition metal catalyzed enantioselective cyclopropanation and hydrosilylation reactions

Copper(I) and rhodium(I) complexes prepared in situ from [Cu(OTf)(C₆H₆)_0.5] and [Rh(cod)Cl]₂ with a range of chiral 2,2′-bipyridines, 5,6-dihydro-1,10-phenanthrolines, 1,10-phenanthrolines and 2,2′:6′,2′′-terpyridines were assessed as chiral catalysts for the enantioselective cyclopropanation of styrene with diazoacetates and for the hydrosilylation of acetophenone with diphenylsilane. Enantioselectivities up to 68% in the cyclopropanation and up to 32% in the hydrosilylation were obtained.     

Biocompatible SuFEx Click Chemistry: Thionyl Tetrafluoride (SOF4)‐Derived Connective Hubs for Bioconjugation to DNA and Proteins

We report here the development of a suite of biocompatible SuFEx transformations from the SOF₄‐derived iminosulfur oxydifluoride hub in aqueous buffer conditions. These biocompatible SuFEx reactions of iminosulfur oxydifluorides (R‐N=SOF₂) with primary amines give sulfamides (8 examples, up to 98 %), while the reaction with secondary amines furnish sulfuramidimidoyl fluoride products (8 examples, up to 97 %). Likewise, under mild buffered conditions, phenols react with the iminosulfur oxydifluorides (Ar‐N=SOF₂) to produce sulfurofluoridoimidates (13 examples, up to 99 %), which can themselves be further modified by nucleophiles. These transformations open the potential for asymmetric and trisubstituted linkages projecting from the sulfur(VI) center, including versatile S?N and S?O connectivity (9 examples, up to 94 %). Finally, the SuFEx bioconjugation of iminosulfur oxydifluorides to amine‐tagged single‐stranded DNA and to BSA protein demonstrate the potential of SOF₄‐derived SuFEx click chemistry in biological applications.