Organocatalytic asymmetric conjugate addition of α-substituted cyanoacetates to maleimides

The asymmetric conjugate addition of α-substituted cyanoacetates to N-substituted maleimides has been developed. A number of cinchona alkaloids and amine thioureas were evaluated as catalysts. Takemoto’s catalyst was found to be the most efficient for the transformation. Chiral succinimides with two adjacent quaternary and tertiary stereogenic carbon centers were obtained in good yields, enantioselectivities, and diastereoselectivities. The products were converted to chiral γ-lactams conveniently without a loss in the enantioselectivity.     

基于两个取代四甲基环戊二烯基配体的金属羰基化合物的合成及晶体结构

配体[C₅Me₄HR][R=4-BrPh(1),(MeC₅H₃N)CH₂(2)]分别与Mo(CO)₆,Ru₃(CO)₁₂和Fe(CO)₅在二甲苯中加热回流,得到了6个双核配合物trans-[η⁵-C₅Me₄R]₂Mo₂(CO)₆(3,4),trans-[(η⁵-C₅Me₄R)Ru(CO)(μ-CO)]₂(5,6)和trans-[η⁵-(C₅Me₄R)Fe(CO)(μ-CO)]₂(7,8,).通过元素分析、红外光谱、核磁共振氢谱对配合物的结构进行了表征,并用X-射线单晶衍射法测定了配合物3,5,6和8的结构.     

Enantioselective synthesis of 10-epi-anamarine via an iterative dihydroxylation sequence

[reaction: see text] The enantioselective syntheses of 10-epi-anamarine and 5,10-epi,epi-anamarine have been achieved in 13 to 14 steps. The route relies upon an enantio- and regioselective Sharpless dihydroxylation of either dienoates or trienoates to establish the C-8 to C-11 stereochemistry. A diastereoselective Leighton allylation established the desired C-5 stereochemistry. The route also relies upon a ring-closing metathesis to establish the alpha,beta-unsaturated lactones.     

Synthesis of tetrasubstituted pyrazines and pyrazine N-oxides

An efficient synthesis of tetrasubstituted unsymmetrical pyrazines and their related pyrazine N-oxides has been developed from commercially available 2-chloro-3-methylpyrazine. The procedure and scope of these synthesis routes are described.     

Novel hydrothermal carbonization of cellulose catalyzed by montmorillonite to produce kerogen-like hydrochar

The conversion of cellulose to petroleum-like fuel is a very challenging yet attractive route to developing biomass-to-fuel technology. Many attempts have been made in liquefaction, pyrolysis and gasification of cellulose to produce fuels or intermediate chemicals. Previous studies indicate that these processes are tough. Hence, the present work is concerned with the development of new technologies for the conversion of cellulose into materials which are analogies to the precursor of petroleum. Montmorillonite-catalyzed hydrothermal carbonization of microcrystalline cellulose for the production of kerogen-like hydrochar under mild conditions was investigated. It was revealed that the hydrothermal carbonization of microcrystalline cellulose alone resulted in hydrochar with type III kerogen-like structure, whereas in the presence of montmorillonite, the hydrothermal carbonization of microcrystalline cellulose yielded a hydrochar-mineral complex, of which the isolated organic fraction was oil-prone type II kerogen-like structure. Results suggested that further improved montmorillonite-aided biomass conversion to more oil-prone kerogen-like solid products could be an alternative efficient route to obtain biofuel and chemicals.     

Effects of flame‐retardant ramie fiber on enhancing performance of the rigid polyurethane foams

Ramie fiber (RF) with excellent tensile strength was treated by a flame retardant and obtained the modified RF (MRF) that is incombustible. Then, MRF was used to improve the performance of rigid polyurethane foams (RPUF). The mechanical properties of the composite were investigated by compressive strength test and shear stress test. The fire characteristics were studied using a cone calorimeter. And the thermal decomposition and flammable properties were further evaluated using thermogravimetric analysis and limiting oxygen index. The results showed that MRF improve the mechanical properties of RPUF and eliminate the harm of flammability of RF on the RPUF.     

Non‐3d Metal Modulation of a Cobalt Imidazolate Framework for Excellent Electrocatalytic Oxygen Evolution in Neutral Media

Cobalt imidazolate frameworks are classical electrocatalysts for the oxygen evolution reaction (OER) but suffer from the relatively low activity. Here, a non‐3d metal modulation strategy is presented for enhancing the OER activity of cobalt imidazolate frameworks. Two isomorphous frameworks [Co₄(MO₄)(eim)₆] (M=Mo or W, Heim=2‐ethylimidazole) having Co(eim)₃(MO₄) units and high water stabilities were designed and synthesized. In different neutral media, the Mo‐modulated framework coated on a glassy carbon electrode shows the best OER performances (1 mA cm^?2 at an overpotential of 210 mV in CO₂‐saturated 0.5 m KHCO₃ electrolyte and 2/10/22 mA cm^?2 at overpotential of 388/490/570 mV in phosphate buffer solution) among non‐precious metal catalysts and even outperforms RuO₂. Spectroscopic measurements and computational simulations revealed that the non‐3d metals modulate the electronic structure of Co for optimum reactant/product adsorption and tailor the energy of rate‐determining step to a more moderate value.     

Visible‐Light‐Induced [4+2] Annulation of Thiophenes and Alkynes to Construct Benzene Rings

The [4+2] annulation represents an elegant and versatile synthetic protocol for the construction of benzene rings. Herein, a strategy for visible‐light induced [4+2] annulation of thiophenes and alkynes, to afford benzene rings, is presented. Under simple and mild reaction conditions, the ready availability and structural diversity of thiophenes and alkynes permit the facile synthesis of several substituted aromatic rings. Valuable drugs and amino acids are also well tolerated. Moreover, DFT calculations explain the high regioselectivity of the reaction.     

Cover Picture: A Stepwise Annulation for the Transformation of Cyclic Ketones to Fused 6 and 7‐Membered Cyclic Enimines and Enones (Chin. J. Chem. 4/2019)

The cover picture shows a typical building within the Campus of Xiamen University displaying Chen Jiageng (Tan Kah Kee)'s style. Just like many beautiful buildings designed and constructed by human, Nature “designs and constructs” a huge number of useful molecules with fascinating structures called natural products. Many natural products possess a fused six or seven‐membered carbocyclic unity. On page 315–322, the Huang's group disclosed a three‐step “[2+n]” annulation method for the construction of fused six and seven‐membered carbocyclic enimines and enones. The method starts from simple cyclic ketones and terminal olefinic amides, and relies on both the Suzuki coupling reaction and the olefin‐amide based Friedel‐Crafts type acylating reaction, a method developed by Huang and coworkers.