共查询到20条相似文献,搜索用时 15 毫秒
1.
Alexander S. Kiselyov 《Tetrahedron letters》2005,46(26):4487-4490
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. 相似文献
2.
C. Wade Downey Alan S. FleisherJames T. Rague Chelsea L. SafranMegan E. Venable Robert D. Pike 《Tetrahedron letters》2011,52(37):4756-4759
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. 相似文献
3.
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. 相似文献
4.
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. 相似文献
5.
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. 相似文献
6.
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. 相似文献
7.
Tanveer Mahamadali Shaikh 《Tetrahedron letters》2009,50(23):2815-4239
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. 相似文献
8.
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. 相似文献
9.
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. 相似文献
10.
A new solid solution system of Al in WC, with the stoichiometry of (W1−xAlx)C (x=0.10, 0.25, 0.50, 0.75, 0.86), has been synthesized by a solid-state reaction between W1−xAlx 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. (W1−xAlx)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 (W1−xAlx)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. 相似文献
11.
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. 相似文献
12.
《Tetrahedron letters》2004,45(14):2943-2945
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. 相似文献
13.
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. 相似文献
14.
Miaojun Wang 《Journal of solid state chemistry》2005,178(4):1182-1189
Lithium substituted Li1+xMn2−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. 相似文献
15.
Braulio M. Fraga Carlo BressaVictoria González-Vallejo Sergio SuárezRicardo Guillermo 《Tetrahedron letters》2011,52(52):7138-7140
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. 相似文献
16.
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. 相似文献
17.
Wen-Jun LiEr-Wei Shi Zhi-Zhan ChenYan-Qing Zhen Zhi-Wen Yin 《Journal of solid state chemistry》2002,163(1):132-136
Superfine Li1−xMn2O4−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 Li0.74Mn2O3.74 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 Li1−xMn2O4−σ powders. The effects of reaction temperature and the contents of NaOH and LiOH on the formation of single phase Li1−xMn2O4−σ were investigated. 相似文献
18.
Mecheril V. Nandakumar 《Tetrahedron》2005,61(41):9775-9782
A Pd2dba3/P(i-BuNCH2CH2)3N catalyzed one-pot synthesis of unsymmetrically substituted trans-4-N,N-diarylaminostilbenes and both symmetrically and unsymmetrically substituted N,N-diarylaminostyrene derivatives is reported. The procedure involves two or more palladium catalyzed sequential coupling reactions (an amination and an inter-molecular Heck reaction) in one-pot using the same catalyst system with two different aryl halides, including aryl chlorides and hetero aryl halides as the coupling partners. 相似文献
19.
Xianhai Huang Ning Shao Anandan Palani Robert Aslanian Alexei Buevich Cynthia Seidel-Dugan Robert Huryk 《Tetrahedron letters》2008,49(22):3592-3595
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. 相似文献
20.
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. 相似文献