Chichibabin pyridinium synthesis

Chichibabin pyridine synthesis involves the reaction of three aldehydes and ammonia to form 2,3,5-trisubstituted pyridines. This study examined the synthesis of tetrasubstituted pyridinium from aldehydes and an amine hydrochloride in the presence/absence of Pr(OTf)₃. Important insights into the reaction mechanisms of Chichibabin pyridinium synthesis were proposed through the investigation of reaction intermediates along with quantitative GC–MS analysis.     

Total synthesis of crotophorbolone

As a natural diterpenoid, crotophorbolone possesses a challenging trans,trans-5/7/6 framework decorated with six contiguous stereogenic centers and is structurally and biogenetically related to tigliane-type diterpenoids with intriguing bioactivities such as phorbol and prostratin. Based on the convergent strategy, we completed an eighteen-step total synthesis of crotophorbolone starting from (−)-carvone and (+)-dimethyl-2,3-O-isopropylidene-l-tartrate. The key elements of the synthesis involve expedient installation of the six-membered ring and the five-membered ring with multiple functional groups at an early stage, cyclization of the seven-membered ring through alkenylation of the ketone between the five-membered ring and the six-membered ring, functional group-sensitive ring-closing metathesis and final selective introduction of hydroxyls at C₂₀ and C₄.

Convergent total synthesis of crotophorbolone was accomplished in 18 longest linear steps. Observation of unexpected thermodynamic stability of a cis,trans-5/7/6 tricycle would benefit synthetic design of tigliane- and daphnane-related diterpenoids.     

Direct synthesis of dimethyl ether from synthesis gas over metal-pillared ilerites

The capability of metal (Cu, Zn)-pillared ilerites and metal oxide (CuO, ZnO)-impregnated metal-pillared ilerites for direct synthesis of dimethyl ether (DME) from synthesis gas was explored. The metal-pillared ilerites were synthesized and characterized by XRD, BET, ICP-AES and SEM. The reaction was carried out in a fixed bed reactor with the prepared catalysts at different temperatures (200, 250, 300°C), 20 bar and H₂/CO ratio of 2. For CuO/Zn-ilerite catalyst, CO conversion was about 62% and selectivity to DME was about 89% at 250°C.     

Microwave-assisted hydrothermal synthesis of low-temperature LiCoO2

A microwave-assisted hydrothermal synthesis route was developed for LT-LiCoO₂ and compared with the conventional hydrothermal synthesis. Our X-ray diffraction, magnetisation, and electron microscopy and electrochemical studies in both cases indicate phase-pure and practically stoichiometric materials with Li-content ≥0.99. The microwave-assisted procedure allows reducing the synthesis temperature down to 170 °C which yields plate-like nano-sized LT-LiCoO₂ compared to the conventionally synthesized micro-scaled material. These differences clearly show-up in the cyclic voltammetry and the galvanostatic intermittent titration technique data which are used for further characterisation of the materials. In both cases, a tiny non-stoichiometry is suggested by the presence of low-temperature small high-spin Co⁴⁺-ions. Our results show that the microwave-assisted process allows lower synthesis temperatures for practically stoichiometric LT-LiCoO₂ which is associated to size-reduction of the resulting crystallites down to the nanometre-scale and a higher fraction of the competing spinel phase.     

介孔炭的孔结构对其负载的Ru基氨合成催化剂性能的影响

采用模板法合成了介孔炭(MC),研究了其孔结构对其负载的Ru基氨合成催化剂Ba-Ru-K/MC性能的影响,采用N₂吸附脱附、扫描电镜和透射电镜等手段对介孔炭的孔结构进行了表征.研究发现,介孔炭载体的孔结构取决于模板剂的用量,当SiO₂/C质量比为1.0时,所制介孔炭比表面积最大.介孔炭负载的Ba-Ru-K催化剂活性与其介孔比表面积相关.在425℃,10MPa和10000h^-1条件下,合成氨的反应速率为139mmol/(g_cat·h).     

Concise formal synthesis of (+)-pyripyropene A

A concise enantioselective synthesis of A/B bicyclic segment of naturally occurring α-pyrone meroterpenoid pyripyropene A is achieved in 9 steps (LLS) and 7.5% yield starting from R-(?)-carvone. The significant points of the synthesis include: (1) an intramolecular 1, 3-dipolar cycloaddition reaction to construct the A ring and assemble C4 quaternary carbon stereocenter as well; (2) reductive cleavage of the oxazole motif utilized Raney Ni/B(OCH₃)₃.     

Microwave-assisted Vilsmeier-Haack synthesis of Pyrazole-4-carbaldehydes

The synthesis of 4-formylpyrazoles using Vilsmeier-Haack reagent is a common protocol in pyrazole chemistry. An efficient microwave-assisted synthesis of 4-formylpyrazoles by employing Vilsmeier-Haack reagent (OPC-VH) derived from phthaloyl dichloride/dimethylformamide has been described. This method offers the advantages of operational simplicity, avoiding the use of POCl₃ as toxic reagents and reuse of the by-product in the preparation of phthaloyl dichloride.     

TiCl4-Et3N-mediated one-step synthesis of γ-alkylidenebutenolides from ketones: Application to natural product synthesis

TiCl₄-Et₃N-mediated condensation of ketones with methyl pyruvate afforded γ-alkylidene butenolides via a tandem cross-aldol addition/dehydroxylation/intramolecular lactonization process in one-pot. The application of the methodology to the straightforward synthesis of elem-1,3,7,8-tetraen-8,12-olide, chloranthalactone A, and dehydromenthofurolactone, is demonstrated.     

Electrochemical synthesis of coatings in the system Ti-Si-B from molten salts

Powder and coatings of metal-like refractory compounds (MLRC) can be produced by electrochemical synthesis from molten salts. The stoichiometry of the deposited MLRC was found to correlate with the molar ratio of MLRC component ions in the melts. The system Ti-Si-B is of particular interest in terms of electrochemical synthesis since the titanium, silicon and boron potentials in the melt are close together. The electrochemical synthesis has been investigated in the system NaCl-KCl-NaF-K₂TiF₆-K₂SiF₆-KBF₄ at 700°C. The opportunity of deposition of new ternary compound in the system Ti-Si-B is shown by the electrochemical synthesis from molten salts.     

Development of high performance Cu/ZnO-based catalysts for methanol synthesis and the water-gas shift reaction

Our groups studies on Cu/ZnO-based catalysts for methanol synthesis via hydrogenation of CO₂ and for the water-gas shift reaction are reviewed. Effects of ZnO contained in supported Cu-based catalysts on their activities for several reactions were investigated. The addition of ZnO to Cu-based catalyst supported on Al₂O₃, ZrO₂ or SiO₂ improved its specific activity for methanol synthesis and the reverse water-gas shift reaction, but did not improve its specific activity for methanol steam reforming and the water-gas shift reaction. Methanol synthesis from CO₂ and H₂ over Cu/ZnO-based catalysts was extensively studied under a joint research project between National Institute for Resources and Environment (NIRE; one of the former research institutes reorganized to AIST) and Research Institute of Innovative Technology for the Earth (RITE). It was suggested that methanol should be produced via the hydrogenation of CO₂, but not via the hydrogenation of CO, and that H₂O produced along with methanol should greatly suppress methanol synthesis. The Cu/ZnO-based multicomponent catalysts such as Cu/ZnO/ZrO₂/Al₂O₃ and Cu/ZnO/ZrO₂/Al₂O₃/Ga₂O₃ were highly active for methanol synthesis from CO₂ and H₂. The addition of a small amount of colloidal silica to the multicomponent catalysts greatly improved their long-term stability during methanol synthesis from CO₂ and H₂. The purity of the crude methanol produced in a bench plant was 99.9 wt% and higher than that of the crude methanol from a commercial methanol synthesis from syngas. The water-gas shift reaction over Cu/ZnO-based catalysts was also studied. The activity of Cu/ZnO/ZrO₂/Al₂O₃ catalyst for the water-gas shift reaction at 523 K was less affected by the pre-treatments such as calcination and treatment in H₂ at high temperatures than that of the Cu/ZnO/Al₂O₃ catalyst. Accordingly, the Cu/ZnO/ZrO₂/Al₂O₃ catalyst was considered to be more suitable for practical use for the water-gas shift reaction. The Cu/ZnO/ZrO₂/Al₂O₃ catalyst was also highly active for the water-gas shift reaction at 673 K. Furthermore, a two-stage reaction system composed of the first reaction zone for the water-gas shift reaction at 673 K and the second reaction zone for the reaction at 523 K was found to be more efficient than a one-stage reaction system. The addition of a small amount of colloidal silica to a Cu/ZnO-based catalyst greatly improved its long-term stability in the water-gas shift reaction in a similar manner as in methanol synthesis from CO₂ and H₂.     

Gas-phase synthesis of inorganic fullerene-like structures and inorganic nanotubes

Following the discovery of fullerenes (C₆₀) and carbon nanotubes, it was shown that nanoparticles of inorganic layered compounds, like WS₂ and MoS₂, are unstable in the planar form and they form closed cage structures with polyhedral or nanotubular shapes. Although initially the method of synthesis for the formation of such closed caged structures and nanotubes involved starting from the respective oxides, it is now well established that the gas-phase synthetic route (using metal chlorides, carbonyls etc) provides an alternative which is suitable for the synthesis of very many closed caged structures and nanotubes hitherto unknown. Various issues with this method of synthesis, including its fundamentals, mechanism, and the properties of the inorganic fullerene-like structures produced are reviewed, together with some possible applications.      

Radical-mediated synthesis of 3,4-dihydroisocoumarins: total synthesis of hydrangenol

A radically promoted synthesis of 3,4-dihydroisocoumarins has been achieved in moderate to good yields using titanocene(III) chloride (Cp₂TiCl) as the radical initiator. The total synthesis of (±)-hydrangenol has been completed using this radical technology. Cp₂TiCl was prepared in situ from commercially available titanocene dichloride (Cp₂TiCl₂) and Zn-dust in THF under argon.     

Direct synthesis and applications of solid silylzinc reagents

The increased synthetic utility of organosilanes has motivated researchers to develop milder and more practical synthetic methods. Silylzinc reagents, which are typically the most functional group tolerant, are notoriously difficult to synthesize because they are obtained by a pyrophoric reaction of silyllithium, particularly Me₃SiLi which is itself prepared by the reaction of MeLi and disilane. Furthermore, the dissolved LiCl in silylzinc may have a detrimental effect. A synthetic method that can avoid silyllithium and involves a direct synthesis of silylzinc reagents from silyl halides is arguably the simplest and most economical strategy. We describe, for the first time, the direct synthesis of PhMe₂SiZnI and Me₃SiZnI reagents by employing a coordinating TMEDA ligand, as well as single crystal XRD structures. Importantly, they can be obtained as solids and stored for longer periods at 4 °C. We also demonstrate their significance in cross-coupling of various free alkyl/aryl/alkenyl carboxylic acids with broader functional group tolerance and API derivatives. The general applicability and efficiency of solid Me₃SiZnI are shown in a wide variety of reactions including alkylation, arylation, allylation, 1,4-addition, acylation and more.

The first direct synthesis of PhMe₂SiZnI and Me₃SiZnI reagents from silyl iodides is described. They can be obtained as solids and stored at 4 °C for extended periods. The versatility of solid Me₃SiZnI is demonstrated in a variety of reactions.     

In situ DRIFTS study on the synthesis of N-alkylmorpholines

In situ diffuse reflectance Fourier-transform infrared spectroscopy was used to perform mechanistic investigation on the synthesis of N-alkylmorpholines from diethylene glycol (DEG), alcohol and ammonia. The results showed that the synthesis of N-alkylmorpholines on a heterogeneous catalyst proceeded along the reaction path between DEG and alkylamine when choosing CuO–NiO/γ-Al₂O₃ as a suitable catalyst. In addition, the yield of methylmorpholine and ethylmorpholine was 86.4 and 76.6 %, respectively.     

A versatile synthesis of vicinal diazides using hypervalent iodine

A convenient synthesis of vicinal diazides from olefins using C₆H₅IO/HOAc/NaN₃ is described. A mechanism is proposed which accounts for the stereochemical outcome.     

Formal synthesis of (±)-brazilin and total synthesis of (±)-brazilane

A convergent synthesis towards (±)-brazilin and (±)-brazilane has been reported from 3,4-dimethoxy benzaldehyde in <15 reaction steps. Palladium(II)-catalysed intramolecular Friedel–Crafts cyclisation and Lewis acid supported intermolecular Friedel–Crafts alkylation reactions have been demonstrated. A tetracyclic substituted indane common key intermediate is employed to furnish the desired two molecules in good to excellent yield. Pd(OH)₂ has played a crucial role in the total synthesis of (±)-brazilane.     

Electrochemical synthesis of thiocarbamates

The possibility of indirect and direct electrosyntheses of thiocarbamates is studied. The indirect synthesis is based on producing monochloramines by the chlorination of an aqueous solution containing an amine and sodium chloride on a dimensionally stable anode (DSA) in diaphragm electrolysis and a subsequent interaction of monochloramines with potassium xanthate. Optimum synthesis conditions are found ensuring a current efficiency for thiocarbamates of 43-60%. These are:c _amine = 0.17-2 M, c_NaC1 = 4 M,j_a = 20-30 A dm^-2, electrolysis temperature 10‡C, the chloramine : potassium xanthate : amine molar ratio of 1 : 1.1 : 2, and the temperature of the reaction between chloramine and potassium xanthate of 8‡C. The direct synthesis of thiocarbamates is realized in diaphragm electrolysis when oxidizing an aqueous solution containing an amine, potassium xanthate, and sodium chloride on DSA. With the electrosynthesis of ethyl ester of methylthiocarbamic acid as an example, conditions are found that allow one to obtain a target product with a current efficiency of about 44%. However, the direct synthesis is accompanied by the destruction of the anode material.     

Nature of active sites in hybrid metal-zeolite catalysts for the Fischer-Tropsch synthesis

The temperature-programmed reduction, powder X-ray diffraction, and oxygen titration were applied to study reducibility, phase composition, and structure of the active surface of the hybrid metal-zeolite catalysts Mβ@Co/Al₂O₃ (M = Pd, Co, and Fe). The results of physicochemical studies were compared with the data on activity and selectivity of the catalysts in the synthesis of liquid hydrocarbons from the synthesis gas. The nature of transition metal and the method of its introduction into the catalyst influence the composition of synthetic liquid hydrocarbons. A comparison of the Feβ@Co/Al₂O₃ catalyst prepared by the ion-exchange method that exhibits the highest activity in the synthesis of liquid hydrocarbons with a similar catalyst Fe/(Hβ@Co/Al₂O₃) prepared by the impregnation method indicated a distinct advantage of the ion exchange procedure. A mechanism of isomerization and cracking of primary linear alkanes on the M _n ^δ+ clusters in the Mβ@Co/Al₂O₃ systems was proposed. The mechanism explains the main features governing the group and fractional composition of the obtained synthetic hydrocarbons.     

An improved synthesis of pennogenin

An improved synthesis of pennogenin, a bioactive component of Chinese herb “Chonglou” (Paris), is described. A ring-switching process opened the ring E of diosgenin and allowed the use of a hydroxyl-directed diboration/oxidation to introduce C17α-OH, hence eliminating the use of OsO₄. This strategy might be rendered to synthesize similar steroids with C17α-OH.     

Accelerated methods of synthesis of phosphorus-containing dendrimers

In order to shorten the long and tedious synthesis of dendrimers, several improvements have been proposed. This paper is a review of the improved methods recently published concerning the synthesis of phosphorus-containing dendrimers. It describes first the synthesis of hyperbranched polymers and their comparison with real dendrimers obtained from the same monomer. Then, the influence of the modification of the core of dendrimers is shown. In a third part, the use of dendrons is illustrated by several examples; they allow for instance to built a generation 8 directly from a generation 3 dendrimer. The last part describes the use of branched monomers of types AB₂ and CD₂, in which A reacts only with D and B reacts only with C. These reactions do not need any protecting groups, and the only by-products are H₂O and N₂. Using these monomers, the 4th generation is obtained in only four steps, instead of 8 for classical methods. This method has been improved by using more branched monomers AB₅ and CD₅, built from the cyclotriphosphazene. In this case, a dendrimer having 750 end groups is obtained in only three steps. The A (NH₂), B (PPh₂), C (N₃) and D (CHO) functions are identical in all cases, and they allow a real “Lego” chemistry, as shown by the synthesis of CA₂ and DB₂ monomers, also used for the accelerated synthesis of dendrimers.