Asymmetric Diels-Alder Reaction Catalyzed by Novel Chiral Dibenzo[a,c]cycloheptadiene Bis(oxazoline) Metal Complexes

A series of novel chiral C 2 symmetric bis(oxazoline) ligands have been synthesized. The copper and magnesium complexes, prepared in situ from copper(II) triflate or magnesium triflate with the new enantiopure oxazoline ligands, were evaluated as chiral catalysts in the enantioselective Diels Alder reaction of cyclopentadiene with N crotenoyl oxazolidin 2 one. Primary results showed that diastereoselectivity up to 94% and enantioselectivity up to 68% ee for endo products were observed respectively with these ligands.

High viscosity of ionic liquids causes rate retardation of Diels-Alder reactions

Second order rate constants, ka have been determined for three bi-molecular Diels-Alder reactions to demonstrate that the high viscosity of ionic liquids can be a detrimental property in carrying out Diels-Alder reactions, if ionic liquids are employed as solvent media. It is possible to enhance the reaction rates of the reaction if a co-solvent is mixed in pure ionic liquid used as a solvent.

A Healable and Mechanically Enhanced Composite with Segregated Conductive Network Structure for High‑Efficient Electromagnetic Interference Shielding

It is still challenging for conductive polymer composite-based electromagnetic interference(EMI)shielding materials to achieve long-term stability while maintaining high EMI shielding effectiveness(EMI SE),especially undergoing external mechanical stimuli,such as scratches or large deformations.Herein,an electrostatic assembly strategy is adopted to design a healable and segregated carbon nanotube(CNT)/graphene oxide(GO)/polyurethane(PU)composite with excellent and reliable EMI SE,even bearing complex mechanical condition.The negatively charged CNT/GO hybrid is facilely adsorbed on the surface of positively charged PU microsphere to motivate formation of segregated conductive networks in CNT/GO/PU composite,establishing a high EMI SE of 52.7 dB at only 10 wt%CNT/GO loading.The Diels–Alder bonds in PU microsphere endow the CNT/GO/PU composite suffering three cutting/healing cycles with EMI SE retention up to 90%.Additionally,the electrostatic attraction between CNT/GO hybrid and PU microsphere helps to strong interfacial bonding in the composite,resulting in high tensile strength of 43.1 MPa and elongation at break of 626%.The healing efficiency of elongation at break achieves 95%when the composite endured three cutting/healing cycles.This work demonstrates a novel strategy for developing segregated EMI shielding composite with healable features and excellent mechanical performance and shows great potential in the durable and high precision electrical instruments.

Catalytic hydrotreatment of humins into cyclic hydrocarbons over solid acid supported metal catalysts in cyclohexane

Humins are common undesirable sideproducts during many acid-catalyzed reactions in renewable biomass platform conversion. However, few studies have been reported to the efficient utilization of humins.For the first time, the selective catalytic conversion of biomass-derived humins into cyclic hydrocarbons with high conversion rate and selectivity is presented using a home-made Ru/W-P-Si-O bifunctional catalyst. The multistage polymerization structure of humins was studied through controlled experiments.Results show that the CAC bond network can be efficiently depolymerized at a mild reaction temperature of 340–380 °C, catalyzed by the cooperative catalysis of nano-Ru particles and porous strong Lewis solid acid. Particularly, 95.4% conversion of humins was achieved under the optimal condition with up to 88.3%yield of cyclic hydrocarbons. The detailed composition after liquefaction was also analyzed. This study paves the way for the efficient production of cyclic and aromatic hydrocarbons from furan-derived humin polymer through Lewis acid-catalyzed Diels–Alder reactions between furan rings.

A bifunctional rosin-derived thiourea catalyzed asymmetric tandem reaction and its new mechanism

A direct asymmetric tandem reaction of a-nitro ketones with b g-unsaturated a-ketoesters was found to be catalyzed by a bifunctional rosin-derived thiourea and gave 5-nitro-2-actoxyl-2-pentenates in excellent ee values and yields,a much better result than previously reported.Furthermore,through theoretical analysis,literature research and experimental verifications,a new mechanism involving an inverse-electron-demand Diels–Alder（IEDDAR） and a retro-Henry reaction was proposed.

Zigzag Hydrocarbon Belts

Zigzag hydrocarbon belts have been fascinating chemists and materials scientists for decades because of their aesthetically appealing molecular structures,outstanding physical properties and intriguing chemical reactivities predicted by theoretical calculations,and potential applications as unique macrocyclic hosts in supramolecular chemistry.They may also serve as templates or seeds to grow structurally well-defined uniform zigzag carbon nanotubes.While there have been continuous computational studies on the structures and properties of belt[n]arenes or[n]cyclacenes since they were proposed as hypothetical molecules in 1954,the synthesis of(partially)conjugated zigzag hydrocarbon belts remains a great challenge,with no progress being reported in the past 20 years.Very recently,we have been witnessing the renaissance of synthetic interest in zigzag hydrocarbon belts,and the formation of the first fully conjugated one is on the horizon.This minireview focuses on the understanding of belt[n]arenes based on theoretical calculations and the synthesis and structure of zigzag hydrocarbon belts.Perspectives on the strategies to isolate and characterize the fully conjugated belt[n]arenes and on the applications of zigzag hydrocarbon belts are also discussed.