Enantioselective conjugate addition of dialkylzinc to cyclic enones catalyzed by chiral binaphthyldiamine-copper(I) complexes

The enantioselective conjugate addition of dialkylzinc (R₂Zn) to cyclic enones was examined using chiral binaphthyldiamine-copper(I) catalysts. Under the present reaction conditions, chiral C₂-symmetric [RZn(II)]₂-diamine-Cu(I) complexes were formed from chiral binaphthyldiamine, R₂Zn, and copper(I or II) chloride in situ. The reaction of 2-cyclohexenone with Et₂Zn proceeded smoothly in the presence of the corresponding chiral copper(I) complex (5 mol %) and achiral 2,6-diphenylaniline (10 mol %), and the desired Et-adduct was obtained with up to 76% ee in 95% yield.     

Enantioselective addition of diethylzinc to N-diphenylphosphinoylimines employing cinchonidine and cinchonine as chiral ligands

The use of the `pseudoenantiomeric pair' of cinchonine and cinchonidine as ligands for the addition of diethylzinc to N-diphenylphosphinoylimines has been investigated. With 1 equiv of cinchonidine as ligand, a series of chiral amines was prepared in good yield and enantiomeric excesses of up to 94%. The use of 2.0 equiv of methanol as an achiral additive was found significantly to improve the selectivity of the addition when using 0.2 equiv of ligand, yielding ee's close to those obtained with a stoichiometric amount of ligand.     

Reductive allylation of 1H-pyridine-2-(thio)ones by means of the novel lithium allyldibutylmagnesate reagent

A new, highly efficient allylation reagent—lithium allyldibutylmagnesate (allylBu₂MgLi)—was obtained by mixing allyl-magnesium chloride (1 equiv) and n-BuLi (2 equiv). N-Lithiated and N-methyl substituted 1H-pyridine-2-thiones and -ones were successfully and regioselectively allylated by treatment with allylBu₂MgLi yielding 6-allyl-3,6-dihydro-1H-pyridine-2-(thio)ones and 4-allyl-3,4-di-hydro-1H-pyridine-2-(thio)ones. The latter were formed by a 3,3-sigmatropic Cope rearrangement of the former.     

4-(tert-Butyldimethylsilyloxy)benzylidene acetal: a novel benzylidene-type protecting group for 1,2-diols

A novel 1,2-diol-protecting group, p-silyloxybenzylidene group, has been developed. In addition to the stepwise deprotection conditions including desilylation and the subsequent acidic hydrolysis of the p-hydroxybenzylidene group in AcOH-THF-H₂O, we have established the one-pot deprotection under basic conditions [K₂CO₃ (5 equiv), NH₂OH·HCl (5 equiv), and CsF (1 equiv) in MeOH-H₂O].     

Nickel-catalysed addition of dialkylzinc reagents to N-phosphinoyl- and N-sulfonylimines

A catalytic amount of a nickel complex (0.1-5.3 mol %) extraordinarily increases the reaction rate of the addition of dialkylzinc reagents to N-(diphenylphosphinoyl)- or N-(benzenesulfonyl)imines. The reaction of imines derived from both aromatic and aliphatic aldehydes with various dialkylzinc reagents in the presence of several nickel complexes gives the expected addition products in most cases in 1 h and in very good yields. In general, the formation of reduction by-products was not an important side reaction. The process represents a great improvement, with regard to the reaction rate and the yield of the addition products, in comparison with the reactions performed in the absence of the nickel catalyst, and reaction times are much shorter than the ones reported so far using other catalysts.     

gem-Difluoropropargylation of aldehydes using cat. In/Zn in aqueous media

Zn (0.9 equiv) in combination with catalytic amounts of In (0.1 equiv) and I₂ (0.1 equiv) was found to effect the reaction of several difluoropropargyl bromide derivatives with aldehydes to produce gem-difluorohomopropargyl alcohols in aqueous media under conditions suitable for large scale applications.     

Microwave-assisted cycloadditions of 2-alkynylbenzonitriles with sodium azide: selective synthesis of tetrazolo[5,1-a]pyridines and 4,5-disubstituted-2H-1,2,3-triazoles

Under microwave irradiation (75 W), treatment of 2-alkynylbenzonitriles with 1.5 equiv of sodium azide in DMSO at 140 °C gave 4,5-disubstituted-2H-1,2,3-triazoles in 60-99% yields. Additionally, adding 8 equiv of ZnBr₂ and using 8 equiv of sodium azide in DMF at 100 °C lead to the formation of tetrazolo[5,1-a]isoquinolines up to 87% yield.     

Metal-free chemoselective oxidation of sulfides by in situ generated Koser’s reagent in aqueous media

Selective oxidation of sulfides was successfully performed by employing phenyliodine diacetate as an oxidant with the catalysis of TsOH in aqueous solution under mild conditions. Sulfoxides were formed with 1.1 equiv of PhI(OAc)₂ at room temperature; whereas sulfones were obtained in the presence of 2.1 equiv of PhI(OAc)₂ at 80 °C under otherwise identical conditions. Notably, various sulfides were converted to corresponding sulfoxides or sulfones in good to high yields by this metal-free protocol.     

Molybdenum oxide/bipyridine hybrid material {[MoO3(bipy)][MoO3(H2O)]}n as catalyst for the oxidation of secondary amines to nitrones

The inorganic-organic hybrid material {[MoO₃(bipy)][MoO₃(H₂O)]}_n (bipy = 2,2′-bipyridine) can be used as a water-tolerant catalyst for the oxidation of secondary amines under mild conditions using either urea hydrogen peroxide (UHP) or tert-butylhydroperoxide (TBHP) as the oxidant. Under optimized reaction conditions (2 mol % catalyst, 3-4 equiv TBHP, CH₂Cl₂ as the solvent, 40 °C), the corresponding nitrones were obtained with different efficiency depending on the nature of the cyclic or acyclic amine used.     

Deprotonation of chloropyridines using lithium magnesates

4-Chloropyridine was deprotonated on treatment with 1/3 equiv of the highly coordinated magnesate Bu₃(TMP)MgLi₂ in THF at −10 °C, as evidenced by trapping with I₂. The use of Bu(TMP)₂MgLi in Et₂O allowed the reaction of 2-chloropyridine, giving the 3-functionalized derivative as the main product. Mixtures of 3- and 4-functionalized derivatives were obtained when 2,6-dichloropyridine was involved in the reaction. Performing the reaction on 3-chloropyridine with lithium magnesates in THF, either the 4,4′-dimer or the 4-iodo derivative was formed after quenching by I₂, the former using 1/3 equiv of Bu₂(TMP)MgLi and the latter using 1 equiv of (TMP)₃MgLi. Similar results were observed with 3,5-dichloropyridine, 2,5-dichloropyridine and 3-chloro-2-fluoropyridine. 1,2-Migration of the lithium arylmagnesate formed by deprotonation was proposed to justify the dimers formation.     

Formation of γ-Fe2O3 nanoparticles and vacancy ordering: An in situ X-ray powder diffraction study

The formation of maghemite, γ-Fe₂O₃ nanoparticles has been studied by in situ X-ray powder diffraction. The maghemite was formed by thermal decomposition of an amorphous precursor compound made by reacting lauric acid, CH₃(CH₂)₁₀COOH with Fe(NO₃)₃·9H₂O. It has been shown that cubic γ-Fe₂O₃ was formed directly from the amorphous precursor and that vacancy ordering starts about 45 min later at 305 °C resulting in a tripled unit cell along the c-axis. The kinetics of grain growth was found to obey a power law with growth exponents n equal to 0.136(6) and 0.103(5) at 305 and 340 °C, respectively. Particles with average sizes of 12 and 13 nm were obtained in 86 and 76 min at 305 and 340 °C, respectively. The structure of cubic and vacancy ordered phases of γ-Fe₂O₃ was studied at 305 °C by Rietveld refinements.     

Synthesis of B-trisubstituted borazines via the rhodium-catalyzed hydroboration of alkenes with N,N′,N″-trimethyl or N,N′,N″-triethylborazine

Hydroboration of terminal and internal alkenes with N,N′,N″-trimethyl- and N,N′,N″-triethylborazine was carried out at 50 °C in the presence of a rhodium(I) catalyst. Addition of dppb or DPEphos (1 equiv.) to RhH(CO)(PPh₃)₃ gave the best catalyst for hydroboration of ethylene at 50 °C, resulting in a quantitative yield of B,B′,B″-triethyl-N,N′,N″-trimethylborazine. On the other hand, a complex prepared from (t-Bu)₃P (4 equiv.) and [Rh(coe)₂Cl]₂ gave the best yield for hydroboration of terminal or internal alkenes.     

Stereoselective aldol additions of titanium enolates of N-acetyl-4-isopropyl-thiazolidinethione

The addition of chlorotitanium enolates of N-acetyl isopropyl thiazolidine-2-thione to aldehydes was investigated. The stereoselectivity of the aldol products was controlled by the number of equivalents of base added. The syn aldol product was obtained preferentially when 2 equiv of Lewis acid and 1 equiv of base were employed. The anti aldol product was obtained preferentially when 1 equiv of Lewis acid and 2 equiv of base were employed for unsaturated aldehydes. Unexpected results were found with hindered aldehydes when 2 equiv of base were employed.     

Synthesis,structure and magnetism of a one-dimensional silicotungstate array: K3H4Cu0.5{Cu[Cu7.5Si2W16O60(H2O)4(OH)4]2} · 9H2O

A structurally distinct, multi-copper(II)-substituted silicotungstate K₃H₄Cu_0.5{Cu[Cu_7.5Si₂W₁₆O₆₀(H₂O)₄(OH)₄]₂} · 9H₂O (1) has been synthesized and characterized by FT-IR spectroscopy, elemental analysis, variable-temperature magnetic measurements, electron spin resonance, and X-ray diffraction. Green crystalline plates of 1 were obtained by the reaction of K₈[γ-SiW₁₀O₃₆] · 12H₂O with 8 equiv. of Cu(II) in a 50% ethylene glycol solution. A cationic copper center connects the terminal oxygen atoms of neighboring polyanions, resulting in a one-dimensional structure. Magnetic susceptibility measurements indicate weak ferromagnetic superexchange between the Jahn–Teller-distorted S = 1/2 Cu(II) centers.     

The first examples of supramolecular discotic C3h tris(N-salicylideneamine)s featuring inter- and intra-molecular H-bonding: synthesis and characterization

Supramolecular liquid crystalline tris(N-salicylideneamine)s (TSANs) featuring both inter- and intra-molecular hydrogen bonding have been synthesized and characterized for the first time. These TSANs formed by condensing 3 equiv of 3,4,5-trialkoxybenzoylhydrazine with 1,3,5-triformylphloroglucinol exist as the single C_3h-symmetric keto-enamine product solely, unlike the previously reported TSANs. Their self-assembly into supramolecular fluid hexagonal columnar phase over a wide thermal range is evidenced with the aid of optical microscopic, calorimetric, and powder X-ray diffraction techniques.     

Synthesis and characterisation of titanium pyridine- and pyrimidine-thiolates and their application as precursors to titanium disulfide

The reaction of TiCl₄ with pyridine- and pyrimidine-thiol has been investigated. Reaction of TiCl₄ with 3 equiv. of 2-mercaptopyridine and 3 equiv. of tert-butylpyridine in toluene at room temperature resulted in the formation of the tris(pyridine-2-thiolate) complex [TiCl(SC₅H₄N)₃] (1). The related reaction between TiCl₄ with 3 equiv. of 2-mercaptopyrimidine and 3 equiv. of tert-butylpyridine in toluene at room temperature resulted in the isolation of the complex [TiCl(SC₄H₃N₂)₃] (2). Compound 2 has been characterised by X-ray crystallography. Low pressure CVD of 1 and 2 produced brown/gold films of TiS₂/TiO₂ on glass substrates at 550 and 600 °C.     

Poly(urethaneimides) (PUIs) containing tertiary amine groups as precursors for original PUI cationomers

This paper details the synthesis and characterisation of poly(urethaneimides) (PUIs) containing tertiary amine groups and obtained from a polytetramethylene oxide diol (PTMO1000), N-methyldiethanolamine (MDEA), 4,4′-methylene-bis-phenylisocyanate (MDI) and 4,4′-hexafluoroisopropylidene-bis-phthalic anhydride (6FDA). The polymers PTMO1000 (1 − x equiv.) + MDEA (x equiv.)/MDI (2 equiv.)/6FDA (1 equiv.) were obtained in high yields (>90%) through original synthesis, involving the reaction of macrodiisocyanates with an aromatic dianhydride in two steps only. A wide range of complementary techniques including two-dimensional NMR showed that the new method enabled a very good control of the polymer structure. In particular, the tertiary amine content of the PUI copolymers was easily varied over the whole composition range (x: 0 → 1), with interesting prospects for the design of a wide range of ion-containing poly(urethaneimides) by quaternising the tertiary amine groups. The PUI properties (e.g. solubility, viscosity, film-forming ability, etc.) clearly depended upon their tertiary amine content. Up to a tertiary amine content of x = 0.7 equiv., the very good film-forming character of the PUIs enabled to cast strong films suitable for permeability investigations.     

The simple solvent-free synthesis of 1H-quinazoline-2,4-diones using supercritical carbon dioxide and catalytic amount of base

Only supercritical carbon dioxide (scCO₂) as a reactant and a solvent, and catalytic amount of base (DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), DBN (1,5-diazabicyclo[4.3.0]non-5-ene), Dabco^® (1,4-diazabicyclo[2.2.2]octane), and triethylamine) afforded 1H-quinazoline-2,4-diones in good to excellent yields from 2-aminobenzonitriles. 6,7-Dimethoxy-1H-quinazoline-2,4-dione, which is a key intermediate of medicines (Prazosin, Bunazosin, and Doxazosin) was synthesized successfully in a 97% yield, using 0.1 equiv of DBU under scCO₂ (10 MPa) at 80 °C.     

Facile nucleophilic fluorination by synergistic effect between polymer-supported ionic liquid catalyst and tert-alcohol reaction media system

A highly efficient method was developed for nucleophilic fluorination using an alkali metal fluoride through the synergistic effect of the polymer-supported ionic liquid (PSIL) as a catalyst and tert-alcohol as an alternative reaction media. This PSIL/tert-alcohol system not only enhances the reactivity of alkali metal fluorides and reduces the formation of by-products but also allows the use of a polymer-supported catalyst protocol. As an example, the nucleophilic fluorinations of the model compound, 2-(3-bromopropoxy)naphthalene, with CsF using only tert-amyl alcohol as solvent (for 2 h reaction time), 0.5 equiv of PS[hmim][BF₄] in CH₃CN (for 12 h reaction time), and 0.5 equiv of PS[hmim][BF₄] in tert-amyl alcohol (which is a PSIL/tert-alcohol system for the synergistic effect; for 2 h reaction time) provided 18, 40, and 84% yield, respectively. The characteristics of the nucleophilic fluorination reactions of some halo- and alkanesulfonyloxyalkane systems to the corresponding fluoroalkanes using various alkali metal fluorides are also reported.     

fac-Acetato-bis(pyrazole) complexes: A systematic study on intra- and intermolecular hydrogen bonds

Acetato-bis(pyrazole) complexes [Mo(η³-methallyl)(O₂CMe)(CO)₂(pz^∗H)₂], (methallyl = CH₂C(CH₃)CH₂) and fac-[M(O₂CMe)(CO)₃(pz^∗H)₂], (pz^∗H = pyrazole or 3,5-dimethylpyrazole, dmpzH; M = Mn, Re) are obtained from [Mo(η³-methallyl)Cl(CO)₂(NCMe)₂] or fac-[MBr(CO)₃(NCMe)₂] [M = Mn (synthesized in situ), Re], 2 equiv. of pyrazole, and 1 equiv. of sodium acetate for Mo complexes, or silver acetate for Mn or Re complexes. The chlorido-complexes [Mo(η³-methallyl)Cl(CO)₂L₂] (L = pzH, dmpzH), obtained from the same starting material by substitution of MeCN by pzH or dmpzH, are also described. The crystal structures of the fac-acetato-bis(dimethylpyrazole) complexes present the same pattern of intramolecular hydrogen bonds between the acetate and the dimetylpyrazole ligands, whereas the crystal structures of the fac-acetato-bis(pyrazole) complexes show different hydrogen bonds patterns, with intermolecular interactions. NMR data indicate that these interactions are not maintained in solution.