Asymmetric allylic C—H functionalization is a valuable and challenging research area. Different from the conventional direct allylic C—H cleavage strategy, transition metal-catalyzed migratory allylic substitution o...Asymmetric allylic C—H functionalization is a valuable and challenging research area. Different from the conventional direct allylic C—H cleavage strategy, transition metal-catalyzed migratory allylic substitution of remote dienes has emerged as a new route to achieve allylic C—H functionalization enantioselectively. This review provides a detailed summary of the development and advance of this strategy, introduces the related mechanistic processes, and discusses the area based on the types of catalysts and products.展开更多
The burgeoning ethylene production in the Asia-Pacific region has led to a substantial oversupply of butadiene as a byproduct,and it is highly important to develop new butadiene-based materials.Butadiene-maleic anhydr...The burgeoning ethylene production in the Asia-Pacific region has led to a substantial oversupply of butadiene as a byproduct,and it is highly important to develop new butadiene-based materials.Butadiene-maleic anhydride copolymer,characterized by its amphiphilic nature,shows potential applications in adhesives,emulsifiers,etc.However,the Diels-Alder(DA)reaction of butadiene and maleic anhydride competes with the polymerization,limiting the copolymer yield.In this study,the kinetics of the DA reaction and copolymerization between butadiene and maleic anhydride were examined,and the influence of various reaction conditions on the copolymer yield was investigated.We found that the DA reaction in the induction period of the radical polymerization was the critical factor in limiting copolymer yield.Therefore,we proposed the two-step method to suppress the DA reaction and achieve high-yield production(~85%)of cross-linked microspheres with controllable particle size(175-800 nm)by self-stabilized precipitation polymerization.This work enables an efficient synthesis of conjugated diolefin-maleic anhydride cross-linked microspheres,offering a novel approach to address the issue of butadiene overcapacity.展开更多
The reaction mechanisms of diene polymerization with homogeneous rare earth catalyst are studied by means of the spectra of ~1H-NMR, one-and two-dimensions ^(13)C-NMR. Based on the data of above NMR spectra, it is pro...The reaction mechanisms of diene polymerization with homogeneous rare earth catalyst are studied by means of the spectra of ~1H-NMR, one-and two-dimensions ^(13)C-NMR. Based on the data of above NMR spectra, it is proposed that the polymerization reaction proceeds according to the following mechanism: η~4-diene (cis-trans-)and η~3-allyl (syn-anti-).展开更多
Because of the widespread applications of optically active alkyl fluorides in medicinal and agro chem-icals,enantioselective and even stereodivergent construction of alkyl fluorides remains highly desirable but underd...Because of the widespread applications of optically active alkyl fluorides in medicinal and agro chem-icals,enantioselective and even stereodivergent construction of alkyl fluorides remains highly desirable but underdeveloped.Transition-metal-catalyzed asymmetric hydrofluoroalkylation of readily available di-enes represents a novel route to achieve this goal,yet receives scarce study.Here we report an intrigu-ing palladium-catalyzed enantioselective hydromonofluoroalkylation reaction of conjugated dienes.Both monosubstituted and internal dienes proceed well with the transformation and furnish alkyl fluorides in generally>80%yield and>90%ee.A stereodivergent hydromonofluoroalkylation protocol via Pd/Cu co-catalysis is also established for the access to all four stereoisomers of corresponding moieties bear-ing a fully-substituted F-stereogenic center and vicinal tertiary carbon center.In addition,asymmetric migratory hydromonofluoroalkylation of skipped dienes is developed to realize the direct allylic C-H flu-oroalkylation.A compound library of enantioenriched cyclic fluorides is thus built to highlight the trans-formation potential of present methodology.展开更多
To meet the increasing demand for safe, environmentally friendly and high-performance smart materials, self-healing rubbers are highly desired. Here, the self-healing performance of ethylene propylene diene monomer ru...To meet the increasing demand for safe, environmentally friendly and high-performance smart materials, self-healing rubbers are highly desired. Here, the self-healing performance of ethylene propylene diene monomer rubber (EPDM) is reported, which was designed by graft-polymerization of zinc dimethacrylate (ZDMA) onto rubber chains to form a reversible ionic cross-linked network. Single ionic cross-linked network and dual network, combining covalent and ionic cross-links, could be tuned by controlling vulcanization process to achieve tailorable mechanical and self-healing properties. It was found that ionic cross-linked EPDM showed a recovery of more than 95% of the original mechanical strength through a healing process of 1 h at 100 °C. The covalent cross-links could improve mechanical properties but block self-healing. Adding 50 wt% liquid rubber to “dry” EPDM could effectively enhance self-healing capability of the dual cross-linked network and the healed tensile strength could reach 0.9 MPa. A compromise between mechanical performance and healing capability could be potentially tailored by controlling vulcanization process and liquid rubber content.展开更多
A series of metal complexes were designed and synthesized and a novel binuclear magnesium complex has been selected, namely [Mg-2(dien)Cl(OH2)(2)]Cl-2 . H2O (dien=diethylene-triamine), which can cleave the plasmid pBR...A series of metal complexes were designed and synthesized and a novel binuclear magnesium complex has been selected, namely [Mg-2(dien)Cl(OH2)(2)]Cl-2 . H2O (dien=diethylene-triamine), which can cleave the plasmid pBR322 DNA effectively in close to physiological condition without adding any external materials. Through biological and chemical methods, especially the comparative experiments, we find the interaction between the complex and DNA belongs to hydrolytic mechanism.展开更多
Herein we reported that ferrocene-containing polymers could be synthesized via acyclic diene metathesis （ADMET） polymerization of ferrocene-containing bis-styryl monomers. The all-trans-configured vinylene bonds of ...Herein we reported that ferrocene-containing polymers could be synthesized via acyclic diene metathesis （ADMET） polymerization of ferrocene-containing bis-styryl monomers. The all-trans-configured vinylene bonds of stilbene segment were proven by means of ^13C-NMR, ^1H-NMR, MALDI-TOF mass spectrometry and FTIR. Poly（1） showed maxima for absorption at 320 nm and emission at 430 nm which are structurally very similar to trans-stilbene, but 24 and 16 nm red shifted respectively. CIE chromaticity diagram shows that emission color could be adjusted by controlling the molecular weight. The polymer showed excellent solubility in common organic solvents and good thermal stability evidenced by TGA and DSC. The results of CV suggested the polymer possessed noninteracting metal centers which was confirmed by a reversible one-electron redox wave observed for the polymer.展开更多
Polymerization of 2-(4-halophenyl)-1,3-butadiene(2-XPB) and their copolymerization with isoprene using a yttrium catalyst have been examined. The β-diketiminato yttrium bis(alkyl) complex(1) activated by [Ph_3 C][B(C...Polymerization of 2-(4-halophenyl)-1,3-butadiene(2-XPB) and their copolymerization with isoprene using a yttrium catalyst have been examined. The β-diketiminato yttrium bis(alkyl) complex(1) activated by [Ph_3 C][B(C_(6) F_(5))_(4)] and Ali Bu3 shows high cis-1,4-selectivity(>98%) for the polymerization of 2-XPB(2-XPB = 2-FPB, 2-Cl PB and 2-Br PB) to afford halogenated plastic poly(dienes) with glass transition temperatures of30–55 ℃. Moreover, the copolymerization of 2-XPB with isoprene(IP) has also been achieved by this catalyst, and the insertion ratios of 2-XPB can be facilely tuned in a full range of 0%–100% simply by changing the 2-XPB-to-IP ratio. Quantitative hydrogenation of cis-1,4-poly(2-XPB) results in perfect alternating ethylene-halostyrene copolymers, and an alternating copolymer of 4-vinylbenzoic acid with ethylene is obtained by a consecutive reaction of ethylene-4-bromostyrene copolymer with ^(n)Bu Li, CO_(2) and HCl.展开更多
Artemisia annua L. produces small amounts of the sesquiterpenoid artemisinin, which is used for treatment of malaria. A worldwide shortage of the drug has led to intense research to increase the yield of artemisinin i...Artemisia annua L. produces small amounts of the sesquiterpenoid artemisinin, which is used for treatment of malaria. A worldwide shortage of the drug has led to intense research to increase the yield of artemisinin in the plant. In order to study the regulation of expression of a key enzyme of artemisinin biosynthesis, the promoter region of the key enzyme amorpha-4,11-diene synthase (ADS) was cloned and fused with the β-glucuronidase (GUS) reporter gene. Transgenic plants of A. annua expressing this fusion were generated and studied. Transgenic plants expressing the GUS gene were used to establish the activity of the cloned promoter by a GUS activity staining procedure. GUS under the control of the ADS promoter showed specific expression in glandular trichomes. The activity of the ADS promoter varies temporally and in old tissues essentially no GUS staining could be observed. The expression pattern of GUS and ADS in aerial parts of the transgenic plant was essentially the same indicating that the cis-elements controlling glandular trichome specific expression are included in the cloned promoter. However, some cis-element(s) that control expression in root and old leaf appears to be missing in the cloned promoter. Furthermore, qPCR was used to compare the activity of the wild-type ADS promoter with that of the cloned ADS promoter. The latter promoter showed a considerably lower activity than the wild-type promoter as judged from the levels of GUS and ADS transcripts, respectively, which may be due to the removal of an enhancing cis-element from the ADS promoter. The ADS gene is specifically expressed in stalk and secretory cells of glandular trichomes of A. annua.展开更多
Ethylene propylene diene elastomers (EPDM) of various side chains and molecular weights were prepared as thin discs and the effects of electric field strength and temperature on the electromechanical properties were i...Ethylene propylene diene elastomers (EPDM) of various side chains and molecular weights were prepared as thin discs and the effects of electric field strength and temperature on the electromechanical properties were investigated. The electrical conductivity, the dielectric constant, the storage and loss moduli (G' and G'), the storage modulus response (ΔG’1000 V/mm), and the storage modulus sensitivity (ΔG’1000 V/mm/G’0) of the elastomers of different ethylene norbornene (ENB) contents and molecular weights were measured under electric field strengths varying from 0 V/mm to 1000 V/mm and at temperatures between 300 K and 380 K. The storage modulus response and sensitivity increase with increasing molecular weight and dielectric constant, consistent with the existing theory. However, for the case of EPDMs with different ENB contents, the storage modulus response and sensitivity vary inversely with the dielectric constant. EDPM is potentially a new type of electroactive materials.展开更多
The addition reaction of p chlorobenzaldoxime dehydrodimer and 1,3 dienes in refluxing chloroform gives linear 1,4 addition products. The reaction is probably a free radical process.
1,3‐Dienes are a class of easily accessible and versatile feedstock chemicals that can participate in a wide range of reactions to facilitate the synthesis of various valuable allylic compounds.In the past decades,ra...1,3‐Dienes are a class of easily accessible and versatile feedstock chemicals that can participate in a wide range of reactions to facilitate the synthesis of various valuable allylic compounds.In the past decades,radical methodology has emerged as a powerful tool for organic synthesis by virtue of the fact that diverse highly reactive radical species can usually be generated under mild,neutral and controlled conditions,and allow for rapid generation of molecular complexity.In this review,we critically illustrate the recent advances in the field of radical‐mediated transformations of 1,3‐dienes based on the different radical precursors and working modes.Wherever possible,particular emphasis is also put on the related mechanistic studies and synthetic applications.展开更多
Asymmetric syntheses of both enantiomerically pure (+) and (-) 5-oxo-endo-tricyclo [5.2.1.0.^(2,6)] deca-3, 8-diene 1 was described. The key step is the use of enzyme-catalyzed hydrolysis of meso-diacetate 5.
New methods for dehydrogenation of steroidal 2,5(10)-dienes with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or pyridinium hydrobromide perbromide(PHP,Py·HBr·Br_2) to aromatic A ring steroid in quantitat...New methods for dehydrogenation of steroidal 2,5(10)-dienes with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or pyridinium hydrobromide perbromide(PHP,Py·HBr·Br_2) to aromatic A ring steroid in quantitative yield in short time are described.展开更多
(η^-C_H_5)_2CeCl_5Mg_2(tmed)_2 was used as a catalyst to polymerize isoprene,Terminal ends of polyisoprene were identified as -CH_2-CH=CH_,which indicates that the insertion reaction of the monomer occurred between ...(η^-C_H_5)_2CeCl_5Mg_2(tmed)_2 was used as a catalyst to polymerize isoprene,Terminal ends of polyisoprene were identified as -CH_2-CH=CH_,which indicates that the insertion reaction of the monomer occurred between η^-allyl and cerium ion and gives a direct evidence for the η^-allyl mechanism of conjugated diene polymerzation with rare earth coordination catalysts.展开更多
文摘Asymmetric allylic C—H functionalization is a valuable and challenging research area. Different from the conventional direct allylic C—H cleavage strategy, transition metal-catalyzed migratory allylic substitution of remote dienes has emerged as a new route to achieve allylic C—H functionalization enantioselectively. This review provides a detailed summary of the development and advance of this strategy, introduces the related mechanistic processes, and discusses the area based on the types of catalysts and products.
基金financially supported by an internal fund from Tsinghua University。
文摘The burgeoning ethylene production in the Asia-Pacific region has led to a substantial oversupply of butadiene as a byproduct,and it is highly important to develop new butadiene-based materials.Butadiene-maleic anhydride copolymer,characterized by its amphiphilic nature,shows potential applications in adhesives,emulsifiers,etc.However,the Diels-Alder(DA)reaction of butadiene and maleic anhydride competes with the polymerization,limiting the copolymer yield.In this study,the kinetics of the DA reaction and copolymerization between butadiene and maleic anhydride were examined,and the influence of various reaction conditions on the copolymer yield was investigated.We found that the DA reaction in the induction period of the radical polymerization was the critical factor in limiting copolymer yield.Therefore,we proposed the two-step method to suppress the DA reaction and achieve high-yield production(~85%)of cross-linked microspheres with controllable particle size(175-800 nm)by self-stabilized precipitation polymerization.This work enables an efficient synthesis of conjugated diolefin-maleic anhydride cross-linked microspheres,offering a novel approach to address the issue of butadiene overcapacity.
基金The Project is supported by "Laboratory of Physics & Chemistry, Academia Sinica" and "National Natural Science Foundation of China"
文摘The reaction mechanisms of diene polymerization with homogeneous rare earth catalyst are studied by means of the spectra of ~1H-NMR, one-and two-dimensions ^(13)C-NMR. Based on the data of above NMR spectra, it is proposed that the polymerization reaction proceeds according to the following mechanism: η~4-diene (cis-trans-)and η~3-allyl (syn-anti-).
基金the National Natural Science Foundation of China(NSFC,No.22071262)Science and Technology Commission of Shanghai Municipality(No.22ZR1475200)+1 种基金Shanghai Rising-Star program(No.20QA1411300)CAS Key Laboratory of Synthetic Chemistry of Natural Substances,and Shanghai Institute of Organic Chemistry for financial support.
文摘Because of the widespread applications of optically active alkyl fluorides in medicinal and agro chem-icals,enantioselective and even stereodivergent construction of alkyl fluorides remains highly desirable but underdeveloped.Transition-metal-catalyzed asymmetric hydrofluoroalkylation of readily available di-enes represents a novel route to achieve this goal,yet receives scarce study.Here we report an intrigu-ing palladium-catalyzed enantioselective hydromonofluoroalkylation reaction of conjugated dienes.Both monosubstituted and internal dienes proceed well with the transformation and furnish alkyl fluorides in generally>80%yield and>90%ee.A stereodivergent hydromonofluoroalkylation protocol via Pd/Cu co-catalysis is also established for the access to all four stereoisomers of corresponding moieties bear-ing a fully-substituted F-stereogenic center and vicinal tertiary carbon center.In addition,asymmetric migratory hydromonofluoroalkylation of skipped dienes is developed to realize the direct allylic C-H flu-oroalkylation.A compound library of enantioenriched cyclic fluorides is thus built to highlight the trans-formation potential of present methodology.
基金financially supported by the National Basic Research Program of China (Nos. 2015CB654700 and 2015CB654706)the National Natural Science Foundation of China (No. 51403115)the Key Laboratory of Rubber-Plastics, Ministry of Education/ Shandong Provincial Key Laboratory of Rubber-plastics of Qingdao University of Science & Technology (KF2017008)
文摘To meet the increasing demand for safe, environmentally friendly and high-performance smart materials, self-healing rubbers are highly desired. Here, the self-healing performance of ethylene propylene diene monomer rubber (EPDM) is reported, which was designed by graft-polymerization of zinc dimethacrylate (ZDMA) onto rubber chains to form a reversible ionic cross-linked network. Single ionic cross-linked network and dual network, combining covalent and ionic cross-links, could be tuned by controlling vulcanization process to achieve tailorable mechanical and self-healing properties. It was found that ionic cross-linked EPDM showed a recovery of more than 95% of the original mechanical strength through a healing process of 1 h at 100 °C. The covalent cross-links could improve mechanical properties but block self-healing. Adding 50 wt% liquid rubber to “dry” EPDM could effectively enhance self-healing capability of the dual cross-linked network and the healed tensile strength could reach 0.9 MPa. A compromise between mechanical performance and healing capability could be potentially tailored by controlling vulcanization process and liquid rubber content.
文摘A series of metal complexes were designed and synthesized and a novel binuclear magnesium complex has been selected, namely [Mg-2(dien)Cl(OH2)(2)]Cl-2 . H2O (dien=diethylene-triamine), which can cleave the plasmid pBR322 DNA effectively in close to physiological condition without adding any external materials. Through biological and chemical methods, especially the comparative experiments, we find the interaction between the complex and DNA belongs to hydrolytic mechanism.
基金financially supported by the National Natural Science Foundation of China(No.21364005)Startup Foundation for Outstanding Young Scientists of Inner Mongolia University(Z20080213No.115110)
文摘Herein we reported that ferrocene-containing polymers could be synthesized via acyclic diene metathesis （ADMET） polymerization of ferrocene-containing bis-styryl monomers. The all-trans-configured vinylene bonds of stilbene segment were proven by means of ^13C-NMR, ^1H-NMR, MALDI-TOF mass spectrometry and FTIR. Poly（1） showed maxima for absorption at 320 nm and emission at 430 nm which are structurally very similar to trans-stilbene, but 24 and 16 nm red shifted respectively. CIE chromaticity diagram shows that emission color could be adjusted by controlling the molecular weight. The polymer showed excellent solubility in common organic solvents and good thermal stability evidenced by TGA and DSC. The results of CV suggested the polymer possessed noninteracting metal centers which was confirmed by a reversible one-electron redox wave observed for the polymer.
基金financially supported by the National Natural Science Foundation of China (Nos. 21634007 and 51773193)the Department of Science and Technology of Jilin Province(No. 20180101171JC)。
文摘Polymerization of 2-(4-halophenyl)-1,3-butadiene(2-XPB) and their copolymerization with isoprene using a yttrium catalyst have been examined. The β-diketiminato yttrium bis(alkyl) complex(1) activated by [Ph_3 C][B(C_(6) F_(5))_(4)] and Ali Bu3 shows high cis-1,4-selectivity(>98%) for the polymerization of 2-XPB(2-XPB = 2-FPB, 2-Cl PB and 2-Br PB) to afford halogenated plastic poly(dienes) with glass transition temperatures of30–55 ℃. Moreover, the copolymerization of 2-XPB with isoprene(IP) has also been achieved by this catalyst, and the insertion ratios of 2-XPB can be facilely tuned in a full range of 0%–100% simply by changing the 2-XPB-to-IP ratio. Quantitative hydrogenation of cis-1,4-poly(2-XPB) results in perfect alternating ethylene-halostyrene copolymers, and an alternating copolymer of 4-vinylbenzoic acid with ethylene is obtained by a consecutive reaction of ethylene-4-bromostyrene copolymer with ^(n)Bu Li, CO_(2) and HCl.
文摘Artemisia annua L. produces small amounts of the sesquiterpenoid artemisinin, which is used for treatment of malaria. A worldwide shortage of the drug has led to intense research to increase the yield of artemisinin in the plant. In order to study the regulation of expression of a key enzyme of artemisinin biosynthesis, the promoter region of the key enzyme amorpha-4,11-diene synthase (ADS) was cloned and fused with the β-glucuronidase (GUS) reporter gene. Transgenic plants of A. annua expressing this fusion were generated and studied. Transgenic plants expressing the GUS gene were used to establish the activity of the cloned promoter by a GUS activity staining procedure. GUS under the control of the ADS promoter showed specific expression in glandular trichomes. The activity of the ADS promoter varies temporally and in old tissues essentially no GUS staining could be observed. The expression pattern of GUS and ADS in aerial parts of the transgenic plant was essentially the same indicating that the cis-elements controlling glandular trichome specific expression are included in the cloned promoter. However, some cis-element(s) that control expression in root and old leaf appears to be missing in the cloned promoter. Furthermore, qPCR was used to compare the activity of the wild-type ADS promoter with that of the cloned ADS promoter. The latter promoter showed a considerably lower activity than the wild-type promoter as judged from the levels of GUS and ADS transcripts, respectively, which may be due to the removal of an enhancing cis-element from the ADS promoter. The ADS gene is specifically expressed in stalk and secretory cells of glandular trichomes of A. annua.
文摘Ethylene propylene diene elastomers (EPDM) of various side chains and molecular weights were prepared as thin discs and the effects of electric field strength and temperature on the electromechanical properties were investigated. The electrical conductivity, the dielectric constant, the storage and loss moduli (G' and G'), the storage modulus response (ΔG’1000 V/mm), and the storage modulus sensitivity (ΔG’1000 V/mm/G’0) of the elastomers of different ethylene norbornene (ENB) contents and molecular weights were measured under electric field strengths varying from 0 V/mm to 1000 V/mm and at temperatures between 300 K and 380 K. The storage modulus response and sensitivity increase with increasing molecular weight and dielectric constant, consistent with the existing theory. However, for the case of EPDMs with different ENB contents, the storage modulus response and sensitivity vary inversely with the dielectric constant. EDPM is potentially a new type of electroactive materials.
文摘The addition reaction of p chlorobenzaldoxime dehydrodimer and 1,3 dienes in refluxing chloroform gives linear 1,4 addition products. The reaction is probably a free radical process.
文摘1,3‐Dienes are a class of easily accessible and versatile feedstock chemicals that can participate in a wide range of reactions to facilitate the synthesis of various valuable allylic compounds.In the past decades,radical methodology has emerged as a powerful tool for organic synthesis by virtue of the fact that diverse highly reactive radical species can usually be generated under mild,neutral and controlled conditions,and allow for rapid generation of molecular complexity.In this review,we critically illustrate the recent advances in the field of radical‐mediated transformations of 1,3‐dienes based on the different radical precursors and working modes.Wherever possible,particular emphasis is also put on the related mechanistic studies and synthetic applications.
文摘Asymmetric syntheses of both enantiomerically pure (+) and (-) 5-oxo-endo-tricyclo [5.2.1.0.^(2,6)] deca-3, 8-diene 1 was described. The key step is the use of enzyme-catalyzed hydrolysis of meso-diacetate 5.
文摘New methods for dehydrogenation of steroidal 2,5(10)-dienes with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or pyridinium hydrobromide perbromide(PHP,Py·HBr·Br_2) to aromatic A ring steroid in quantitative yield in short time are described.
文摘(η^-C_H_5)_2CeCl_5Mg_2(tmed)_2 was used as a catalyst to polymerize isoprene,Terminal ends of polyisoprene were identified as -CH_2-CH=CH_,which indicates that the insertion reaction of the monomer occurred between η^-allyl and cerium ion and gives a direct evidence for the η^-allyl mechanism of conjugated diene polymerzation with rare earth coordination catalysts.
