A novel three-component reaction of N-fluoropyridinium salts: a facile approach to imidazo[1,2-a]pyridines

The reaction of N-fluoropyridinium triflate with isonitriles in acetonitrile and propionitrile in the presence of NaBH(OAc)₃ led to the formation of the corresponding imidazo[1,2-a]pyridines in 44-73% yields. The proposed reaction mechanism involves the intermediate formation of a highly reactive carbene species and apparent reduction of the pyridinium intermediate with NaBH(OAc)₃ to yield the targeted heterocycles.     

Synthesis of N-acyl-N,O-acetals from N-aryl amides and acetals in the presence of TMSOTf

Secondary amides undergo in situ silyl imidate formation mediated by TMSOTf and an amine base, followed by addition to acetal acceptors to provide N-acyl-N,O-acetals in good yields. An analogous, high-yielding reaction is observed with 2-mercaptothiazoline as the silyl imidate precursor. Competing reduction of the acetal to the corresponding methyl ether via transfer hydrogenation can be circumvented by the replacement of CY₂NMe with 2,6-lutidine under otherwise identical reaction conditions.     

Concise synthesis of multiply substituted stereodefined cis,cis-2,4-diene-1,6-dials, cis,cis-2,4-diene-1,6-diols and further applications

Reactions of 1,4-dilithio-1,3-dienes with DMF afforded multiply substituted stereodefined cis,cis-2,4-diene-1,6-dials in high yields. Treatment of these 1,6-dials with LiAlH₄ or RLi resulted in the formation of their corresponding 1,6-diols. These bifunctional compounds, cis,cis-2,4-diene-1,6-dials and -1,6-diols are otherwise not readily available. Further reaction of these 1,6-diols with an aldehyde catalyzed by strong acids led to the formation of oxacycles of novel structures.     

Characterization of CdS nanoparticles in solutions of P(TFE-co-PVDF-co-Prop)/N,N-dimethylformamide

We report in here the preparation of CdS nanoparticles (Q-CdS) in N,N-dimethylformamide (DMF) and poly(tetrafluoroethylene-co-vinylidenefluoride-co-propylene) (PTFE-co-PVDF-co-Prop) by reaction of cadmium acetate and thiourea at room temperature. The formation and size evolution of Q-CdS particles were followed by optical absorption spectroscopy as a function of the aging process of the solutions. The obtained results indicated that not only the Q-CdS particles were more stable in DMF than in aqueous solutions, probably due to the interaction with the CHNO group, but also they were formed in smaller sizes. The particle size obtained in DMF was estimated in 4-6 nm against 10-20 nm in aqueous solution. The results also showed that the velocity of Q-CdS formation is lower when the reaction was carried out in PTFE-co-PVDF-co-Prop dissolved in DMF. The Q-CdS particles formed in this system were also less stable than in pure DMF, probably due to the interaction of the CHNO fragment and CF₂ of polymer chain or phase segregation.     

Synthesis and X-ray structural characterization of the triphenylphosphine derivative of the closo-dodecaborate anion, closo-[B12H11P(C6H5)3][N(n-C4H9)4]

The reaction of a molar excess of closo-[B₁₂H₁₁I][N(n-C₄H₉)₄]₂ (1) with tetrakis(triphenylphosphine)palladium (0), Pd(0)L₄, yields to the formation of the title monoanionic compound, closo-[1-B₁₂H₁₁P(C₆H₅)₃][N(n-C₄H₉)₄] (2). The structure of 2 was determined by X-ray diffraction analysis performed on a single crystal. The mechanism of formation of 2 is also discussed. We suggested a two-step mechanism for the formation of 2 consisting in a oxidative addition of the palladium complex followed by a reductive elimination involving P(C₆H₅)₃ and assisted by Na₂CO₃. To our knowledge, this is the first example of monosubstitution of B₁₂ with formation of boron-phosphorus bond.     

Titanium superoxide: a heterogeneous catalyst for anti-Markovnikov aminobromination of olefins

A new facile procedure for the aminobromination of olefins in high yields has been described using p-toluene sulfonamide (p-TsNH₂) and N-bromosuccinimide (NBS) as nitrogen and bromine sources, respectively, and titanium superoxide as a truly heterogeneous catalyst. The formation of anti-Markovnikov product exclusively in all the cases studied possibly proceeding through a free radical reaction pathway is remarkable.     

Superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids: synthesis of quinolin-2(1H)-one derivatives

The superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids by Bronsted superacids (CF₃SO₃H, HSO₃F) or strong Lewis acids AlX₃ (X=Cl, Br) results in the formation of 4-aryl quinolin-2(1H)-ones in quantitative yields. The vinyl triflates or vinyl chlorides may be formed as additional reaction products. The investigated amides in reactions with benzene give 4,4-diaryl 3,4-dihydroquinolin-2-(1H)-ones under the superelectrophilic activation. 4-Aryl quinolin-2(1H)-ones in POCl₃ are converted into 4-aryl 2-chloroquinolines. 4-Fluorophenyl-4-phenyl 3,4-dihydroquinolin-2-(1H)-one give N-formylation products in a yield of 79% under the Vilsmeier–Haack reaction conditions.     

Synthesis and characterization of La2Mo2O9 obtained from freeze-dried precursors

La₂Mo₂O₉ ceramics have been prepared from freeze-dried precursors and their properties compared to those of lantanum molybdate obtained by conventional solid state (SS) reaction. All materials have been characterized by X-ray diffraction, scanning electron microscopy and thermal analysis (TGA/DTA/DSC and dilatometry) to characterize the phase formation and phase transition. When the freeze-dried method was applied, the synthesis temperature required to obtain dense samples was much lower than that for powders obtained by SS reaction. The morphology and structure of the oxide particle are significantly dependent on the synthesis method. The grain size is smaller, whereas the density of sintered pellets is higher for the freeze-dried precursor powder when compared with the SS reaction method. Impedance spectroscopy was used to measure the electrical conductivity of La₂Mo₂O₉ from 548 to 1123 K, in air, and to characterize the blocking effects of grain boundaries.     

Synthesis, crystal structure, and density of (W1−xAlx)C

A new solid solution system of Al in WC, with the stoichiometry of (W_1−xAl_x)C (x=0.10, 0.25, 0.50, 0.75, 0.86), has been synthesized by a solid-state reaction between W_1−xAl_x alloys and carbon at around 1673 K in vacuum. Environment scanning electron microscope, energy-dispersive analysis of X-ray, X-ray photoelectron spectroscopy, and inductively coupled plasma analyses are used to certify the formation of the products. The mechanism of the solid-state reaction is also discussed. (W_1−xAl_x)C is identified to crystallize in the hexagonal space group P6m2 (No. 187) and belongs to the WC structure type. The atoms of W and Al occupy the same lattice site (1a site) in the cell of (W_1−xAl_x)C. The cell parameters for each specimen in the phase of W-Al-C are quite close to that of WC, while their densities are far lower than that of WC.     

Chemistry of odorants: stereoselective synthesis of octahydronaphthalene-based perfumery Georgywood, (+,−)-1-[(1R,2S)-1,2,3,4,5,6,7,8-octahydro-1,2,8,8-tetramethylnaphthalen-2-yl]ethan-1-one

A straightforward synthesis of octahydronaphthalene-based fragrance, such as Georgywood, is described. The Lewis acid tin (IV) chloride catalyzed efficiently an original one-pot sequential cycloaddition-clyclization process by reaction of myrcene with 3-bromo-but-3-en-2-one, leading directly to the octahydronaphthalene skeleton in very good yields (85%). Then, dehydrohalogenation with DBU gave the key 2,4-dienone intermediate in excellent yield (85%). Regioselective Michael addition gave rise to the formation of the addition product as a trans/cis diastereoisomeric mixture, by reaction either with CH₃Cu·BF₃ (6:1 ratio, 70%) or (CH₃)₂CuLi/TMSCl reagents (3:1 ratio, 80%). The generation of thermodynamically more stable enolate by treatment of the diastereoisomeric mixture with sodium hydride in tetrahydrofuran in the presence of an excess of methyl iodide, allowed stereoselective introduction of the methyl group at C2, leading to the formation of Georgywood in good yield (60%), as the only diastereoisomer, with a trans stereochemistry of the two methyl groups as demonstrated by NMR experiments.     

Access to lincomycin N-oxide isomers controlled by reaction conditions

Oxidation of lincomycin with H₂O₂ in alkaline media leads to N-oxides, besides the conversion of thiomethyl group into sulfoxides and sulfones. NH₄OH favors formation of the S-isomer; both R- and S-isomers of the N-oxide are formed in the presence of NaOH. Addition of acetonitrile markedly accelerates the reaction.     

Facile stereoselective synthesis of cis- and trans-3-alkoxyazetidin-2-ones

A highly stereoselective synthesis of cis- and trans-3-alkoxy-3-phenyl/benzylthioazetidin-2-ones is described. The reaction of α-chlorosulfide-β-lactams with various alcohols catalyzed by a Lewis acid such as ZnCl₂ in the presence of molecular sieves (3-4 Å) leads to cis-3-alkoxy-3-phenyl/benzylthio-β-lactams whereas treatment of potassium 2-alkoxy-2-phenylthioethanoate with appropriate Schiff's base using POCl₃ in the presence of triethylamine leads to the formation of trans-3-alkoxy-3-phenylthioazetidin-2-ones as major products.     

Thermochemistry of Li1+xMn2−xO4 (0?x?1/3) spinel

Lithium substituted Li_1+xMn_2−xO₄ spinel samples in the entire solid solution range (0?x?1/3) were synthesized by solid-state reaction. The samples with x<0.25 are stoichiometric and those with x?0.25 are oxygen deficient. High-temperature oxide melt solution calorimetry in molten 3Na₂O·4MoO₃ at 974 K was performed to determine their enthalpies of formation from constituent binary oxides at 298 K. The cubic lattice parameter was determined from least-squares fitting of powder XRD data. The variations of the enthalpy of formation from oxides and the lattice parameter with x follow similar trends. The enthalpy of formation from oxides becomes more exothermic with x for stoichiometric compounds (x<0.25) and deviates endothermically from this trend for oxygen-deficient samples (x?0.25). This energetic trend is related to two competing substitution mechanisms of lithium for manganese (oxidation of Mn³⁺ to Mn⁴⁺ versus formation of oxygen vacancies). For stoichiometric spinels, the oxidation of Mn³⁺ to Mn⁴⁺ is dominant, whereas for oxygen-deficient compounds both mechanisms are operative. The endothermic deviation is ascribed to the large endothermic enthalpy of reduction.     

Mild method for the synthesis of 1H-indazoles through oxime-phosphonium ion intermediate

The synthesis of 1H-indazoles from o-aminobenzoximes is achieved via N–N bond formation using triphenylphosphine, I₂, and imidazole. Selective formation of oxime-phosphonium ion intermediate in the presence of the amino group is the driving force for this reaction. The nucleophilicity of the arylamino group and electrophilicity toward the N–O bond of oxime also control the reaction. The reaction proceeds at a faster rate with good to excellent yield under this mild reaction condition and is amenable to scale-up.     

Solvothermal Synthesis of Superfine Li1−xMn2O4−σ Powders

Superfine Li_1−xMn₂O_4−σ powders were successfully synthesized by the alcohol-thermal method using 0.01 mol of MnO₂, 0.01mol of LiOH·H₂O, and 0.06mol of NaOH as starting materials at 160-200°C. The products are characterized by XRD, TEM, ED, BET, and ICP. Results show that the Li_0.74Mn₂O_3.74 powder prepared at 200°C has an average size of 180 nm with BET surface areas of 16.44 m²/g. A possible formation mechanism is proposed. It was concluded that the alcohol acts not only as the solvent but also as the reducing agent in the synthesis of Li_1−xMn₂O_4−σ powders. The effects of reaction temperature and the contents of NaOH and LiOH on the formation of single phase Li_1−xMn₂O_4−σ were investigated.     

Neighbouring group participation in the reaction of 7-oxo-ent-kaur-16-ene derivatives with diacetoxyiodobenzene. Synthesis of gibberellin analogues

The reaction of different 7-oxo-ent-kaur-16-ene derivatives with diacetoxyiodobenzene has been evaluated for the preparation of gibberellin analogues. Thus, the reaction of 7-oxo-ent-kaur-16-en-18-oic acid methyl ester (3) with this reagent afforded 4-epi-GA₁₂ dimethyl ester (6). This reaction constitutes a good procedure for the preparation of this type of compounds. In some cases, alternative reactions that led to the introduction in the substrate of a conjugated 5,6-double bond or to the formation of a ketal at the 6-position were also produced. The formation of these compounds, or of gibberellin analogues, depends on the neighbouring group participation of the different C-18 and C-19 substituents at C-4.     

Synthesis of seco-psymberin/irciniastatin A: the discovery of a novel PhI(OAc)2 mediated cascade cyclization reaction

The psymberin unsaturated ‘psymberate’ side chain 7 was synthesized in 7 steps (36% yield) with good diastereoselectivity using commercially available starting material to control the stereochemistry at C₄ and C₅. The synthesis of seco-psymberin was completed in an efficient manner based on a CuI mediated coupling reaction between vinyl iodide 8 and ‘psymberamide’ 7. In an attempt to synthesize natural psymberin from the seco-intermediate, a novel PhI(OAc)₂ mediated cascade ring closing reaction was discovered. A possible mechanistic pathway for the formation of the ring closing product was presented.     

Sm(OTf)3 as a highly efficient catalyst for the synthesis of 2,3-unsaturated O- and S-pyranosides from glycals and the temperature-dependent formation of 4-O-acetyl-6-deoxy-2,3-unsaturated S-pyranosides and 4-O-acetyl-6-deoxy-3-alkylthio glycals

By using Sm(OTf)₃ as the catalyst, synthesis of 2,3-unsaturated-glycosides has been performed. A series of 2,3-unsaturated glycosides were obtained from 3,4,6-tri-O-acetyl–d-glucal or 3,4-di-O-acetyl-l-rhamnal under mild reaction conditions in good yield and high anomeric selectivity. It was found that under certain conditions, reaction of 3,4-di-O-acetyl-l-rhamnal with thiol leads to temperature-dependent formation of C-1-S and C-3-S product. A temperature-dependent profile of the yield of these two products is given.     

Unexpected course of rearrangement of substituted S-(1(3H)-isobenzofuranone-3-yl)isothiuronium bromides

Three series of S-(1(3H)-isobenzofuranone-3-yl)isothiuronium bromides differing in substitution at the isothiuronium moiety (none, one or two methyl groups) and at the benzene ring were prepared and characterized. These salts were then treated with various bases (acetate, triethylamine, Na₂CO₃) to give either 1-hydroxy-3-oxo-1,3-dihydro-2H-isoindol-2-carbothioamides or the product of S to N isobenzofuranone-3-yl migration, i.e., 1,3-dimethyl-1-(3-oxo-1,3-dihydro-2-benzofuran-1-yl)thioureas. If ammonia was used in reaction with N,N′-dimethyl isothiuronium salts then 3-hydroxy-2,3-dihydro-1H-isoindol-1-ones were formed together with 1,3-dimethyl-1-(3-oxo-1,3-dihydro-2-benzofuran-1-yl)thioureas in parallel reaction with the yields increasing with ammonia concentration. The formation of isoindolones takes place in two steps with an aldehyde intermediate, which can be trapped with N,N-dimethylhydrazine.     

Synthesis of meso-tetraphenyl porphyrins via condensation of dipyrromethanes with N-tosyl imines

A new synthetic route for the synthesis of 5,10,15,20-tetraphenyl porphyrins has been developed based on the reaction of 5-substituted dipyrromethanes with N-tosyl imines in the presence of a metal triflate catalyst. meso-Substituted tetraphenyl porphyrins were synthesized in a two-step process. The first step of the method is the metal triflate-catalyzed condensation of 5-substituted dipyrromethanes with N-tosyl imines to form a porphyrinogen intermediate and the second step is the oxidation of the porphyrinogen to porphyrin. The method was applied to the synthesis of trans-A₂B₂-tetraarylporphyrins and the products were obtained with only a trace amount of one scrambling product. The synthesis of two important building blocks for porphyrin synthesis, mono and di-sulfonamide alkylated 5-substituted dipyrromethanes, was achieved by the addition of 5-substituted dipyrromethane to N-tosyl imine. The application of mono and di-sulfonamide alkylated 5-substituted dipyrromethanes in ‘2+2’ porphyrin formation reactions is presented.