The development of catalytic asymmetric methods that enable access to value-added functionalities or structures,exemplified by allylic alcohols,is a highly interesting yet challenging topic from both academic and indu...The development of catalytic asymmetric methods that enable access to value-added functionalities or structures,exemplified by allylic alcohols,is a highly interesting yet challenging topic from both academic and industrial perspectives.However,before recent advances in chemical catalysis,there were scarce protocols toward constructing enantioenriched tertiary allylic alcohol scaffolds.In this context,peptide-mimic phosphonium salts were found to be highly efficient in catalytic asymmetricα-hydroxylation ofα,β-unsaturated and/orβ,Y-unsaturated compounds with satisfactory regio-and stereochemical outcomes(up to 97%yield and 95%ee).This methodology tolerates a broad array of substrates and thus provides an expeditious and unified platform for the assembly of enantioenriched tertiary allylic alcohols by avoiding the use of additional reductants and expensive metal catalysts.Furthermore,the power of this protocol is enlarged by simple conditions and the use of air as a source of hydroxyl functionality.展开更多
Chiral quaternary phosphonium ion-pair catalysis showcases a distinctive catalytic and stereoinductive mode arising from the synergy between ionic and noncovalent interactions.Over recent decades,this methodology has ...Chiral quaternary phosphonium ion-pair catalysis showcases a distinctive catalytic and stereoinductive mode arising from the synergy between ionic and noncovalent interactions.Over recent decades,this methodology has been widely adopted to facilitate enantioselective nucleophilic addition reactions,including conjugate addition,Henry reaction,Mannich reaction,Strecker reaction,and hydrophosphonylation.This strategy has been successfully applied to the synthesis of numerous structurally diverse and multifunctionalized molecules,featuring challenging stereogenic centers.This minireview specifically highlights the accomplishments in asymmetric nucleophilic addition facilitated by chiral quaternary phosphonium catalysts.Its purpose is to cultivate interest among researchers,encouraging more engagement in this field and establishing quaternary phosphonium ion-pair catalysis as a potent and dependable tool for synthetic and pharmaceutical chemists.展开更多
Hydroclimatic variations over the eastern Central Asia are highly sensitive to changes in hemispheric-scale atmospheric circulation systems. To fully understand the long-term variability and relationship between hydro...Hydroclimatic variations over the eastern Central Asia are highly sensitive to changes in hemispheric-scale atmospheric circulation systems. To fully understand the long-term variability and relationship between hydroclimate and atmospheric circulation system, we present a high-resolution lascustrine record of late Holocene hydroclimate from Lake Sayram, Central Tianshan Mountains, China, based on the total organic carbon, total nitrogen, and carbonate contents, carbon/nitrogen ratios, and grain size. Our results reveal four periods of substantially increased precipitation at the interval of 4000–3780, 3590–3210, 2800–2160, and 890–280 cal yr BP, and one period of slightly increased precipitation from 1700–1370 cal yr BP. These wetter periods broadly coincide with those identified in other records from the mid-latitude Westerlies-dominated eastern Central Asia, including the northern Tibetan Plateau. As such, a similar hydroclimatic pattern existed over this entire region during the late Holocene. Based on a close similarity of our record with reconstruction of North Atlantic Oscillation indices and solar irradiance, we propose that decreased solar irradiance and southern migration of the entire circum-North Atlantic circulation system, particularly the main pathway of the mid-latitude Westerlies, significantly influenced hydroclimate in eastern Central Asia during the late Holocene. Finally, the inferred precipitation at Lake Sayram has increased markedly over the past 100 years, although this potential future changes in hydroclimate in Central Asia need for further investigation.展开更多
Since Homo sapiens appeared,the planet has experienced continuing environmental changes[1,2].In 2000,Crutzen and Stoermer[3]systematically analysed the global changes caused by human activity over the previous 300 yea...Since Homo sapiens appeared,the planet has experienced continuing environmental changes[1,2].In 2000,Crutzen and Stoermer[3]systematically analysed the global changes caused by human activity over the previous 300 years and suggested that the Holocene epoch ended in the 1750s and a new geological age,the Anthropocene,began.Afterwards,the Anthropocene drew a lot of attention from both scientific community and the general public.The recognition and placement of the Anthropocene/Holocene boundary has been a subject of heated debates over the past two decades.At the 35th International Geological Congress(2016;IGC),the Anthropocene Working Group(AWG)recommended the Anthropocene to be formalised with an epoch rank,with the 1950s as its lower boundary[4].展开更多
Evaluating anthropogenic impacts on regional vegetation changes during historical time is not only important for a better understanding of the Anthropocene but also valuable in improving the vegetation-climate models....Evaluating anthropogenic impacts on regional vegetation changes during historical time is not only important for a better understanding of the Anthropocene but also valuable in improving the vegetation-climate models.In this study,we analyzed stable isotopes(δ^18O,δ^13C)and trace elements(Mg/Ca,Sr/Ca)of a stalagmite from Huangchao Cave in central Shandong,northern China.230Th and AMS14C dating results indicate the stalagmite deposited during 174BC and AD1810,with a hiatus between AD638 and 1102.Broad similarities of theδ^18O and trace elements in the stalagmite suggest they are reliable precipitation indexes.Theδ^13C of the stalagmite,a proxy of vegetation change,was generally consistent with local precipitation and temperature variations on a centennial-scale before the 15th century.It typically varied from–9.6‰to–6.3‰,indicating climate controlled C3 type vegetation during this period.However,a persistent and marked increasing trend in theδ^13C record was observed since the 15th century,resulting inδ^13C values from–7.7‰to–1.6‰in the next four centuries.This unprecedentedδ^13C change caused by vegetation deterioration cannot be explained by climate change but is fairly consistent with the dramatically increasing population and farmland in Shandong.We suggest that the increasing deforestation and reclamation in central Shandong began to affect vegetation in the mountain region of central Shandong since the 15th century and severely destroyed or even cleared the forest during the 16th–18th century.展开更多
Stereodivergently constructing the designed products having adjacent multi-stereocenters via a given reaction,with excellent control of both absolute and relative configurations,presents one of the substantial hurdles...Stereodivergently constructing the designed products having adjacent multi-stereocenters via a given reaction,with excellent control of both absolute and relative configurations,presents one of the substantial hurdles in asymmetric catalysis.Herein,we report a precisely stereodivergent asymmetric protocol by synergistic combination of phosphonium-involved ion-pair catalysis and base for accessing to chiral phosphorus compounds bearing two adjacent chiral centers particularly containing an acidic protonated enantioenriched carbon atom,having broad functional group compatibility in both dynamic and thermodynamic processes under mild reaction conditions.Two keys for the success in constructing these stereoisomers with high levels of regio-,diastereo-,and enantioselectivities were contained:firstly,the precise stereo-control in providing dynamic products was enabled by bifunctional phosphonium salt catalyst with semi-enclosed cavity;secondly,the readily stereospecific transformation of adducts from dynamic to thermodynamic version was initiated by achiral base.All four stereoisomers could be readily accessed even in gram-scale in high yields with maintaining excellent stereoselectivities,illustrating the potential of this synergistic catalytic methodology in organic synthesis.Moreover,mechanistic studies including density functional theory(DFT)calculations and control experiments provide insights into the mechanism.展开更多
Structurally fused heterocycles encompassing a centerpiece of benzotropane are significant scaffolds with a plethora of promising biological activities,but such molecular architectures pose a long-standing daunting sy...Structurally fused heterocycles encompassing a centerpiece of benzotropane are significant scaffolds with a plethora of promising biological activities,but such molecular architectures pose a long-standing daunting synthetic challenge.Herein,we reported a highly efficient asymmetric cyclodearomatization of 2-nitrobenzofurans with cyclic azomethine ylides by employing bifunctional phosphonium salts as phase-transfer catalysts.Under optimized reaction conditions,a diverse array of polycyclic benzofused tropane derivatives with four contiguous 4°/3°stereocenters were readily synthesized in both high yields and diastereoselectivities with up to>99%ee.The practicality and utility of this protocol were further demonstrated by the scaled-up reaction and facile elaborations.Moreover,preliminary investigations into their antitumor activities were also presented.展开更多
We present a phosphonium-containing catalyst generated in situ from phosphine and tert-butyl acrylate that serves as an unusual Lewis base catalyst.It was applied for the promotion of a remote 1,6-cyanation reaction o...We present a phosphonium-containing catalyst generated in situ from phosphine and tert-butyl acrylate that serves as an unusual Lewis base catalyst.It was applied for the promotion of a remote 1,6-cyanation reaction of p-quinone methides and fuchsones employing trimethylsilyl cyanide as the cyanide source.A diverse range ofα-diaryl andα-triaryl acetonitriles was obtained in high yields under mild reaction conditions with low catalyst loading(5 mol%).The practicality and utility of this protocol were demonstrated via the gram-scale preparation and facile elaboration of products.Mechanistic investigations(in situ NMR and ESI-MS analysis)were employed to characterize the active zwitterionic phosphonium intermediate,which was the“true”active catalyst.展开更多
基金Financial support was provided by the National Natural Science Foundation of China(22222109,21921002,22101189 and 22371190)the National Key R&DProgramof China(2018YFA0903500)+3 种基金Beijing National Laboratory for Molecular Sciences(BNLMs202101)Sichuan Science Foundation for Distinguished Young Scholars(2023NSFSC1921)Sichuan Provincial Natural Science Foundation(2022NSFSC1181,24NSFSC6590)Fundamental Research Funds from Sichuan University(2020SCUNL108)and Fundamental Research Funds for the Central Universities.
文摘The development of catalytic asymmetric methods that enable access to value-added functionalities or structures,exemplified by allylic alcohols,is a highly interesting yet challenging topic from both academic and industrial perspectives.However,before recent advances in chemical catalysis,there were scarce protocols toward constructing enantioenriched tertiary allylic alcohol scaffolds.In this context,peptide-mimic phosphonium salts were found to be highly efficient in catalytic asymmetricα-hydroxylation ofα,β-unsaturated and/orβ,Y-unsaturated compounds with satisfactory regio-and stereochemical outcomes(up to 97%yield and 95%ee).This methodology tolerates a broad array of substrates and thus provides an expeditious and unified platform for the assembly of enantioenriched tertiary allylic alcohols by avoiding the use of additional reductants and expensive metal catalysts.Furthermore,the power of this protocol is enlarged by simple conditions and the use of air as a source of hydroxyl functionality.
基金Financial support was provided by the National Natural Science Foundation of China(grant nos.22222109,21921002,22101189,21897002,and 31972290)the Beijing National Laboratory for Molecular Sciences(grant no.BNLMS202101)+2 种基金the Natural Science Foundation of Sichuan Province(grant nos.2023NSFSC1921,2022NSFSC1181,and 24NSFSC6590)the Fundamental Research Funds from Sichuan University(grant no.2020SCUNL108)the Fundamental Research Funds for the Central Universities.
文摘Chiral quaternary phosphonium ion-pair catalysis showcases a distinctive catalytic and stereoinductive mode arising from the synergy between ionic and noncovalent interactions.Over recent decades,this methodology has been widely adopted to facilitate enantioselective nucleophilic addition reactions,including conjugate addition,Henry reaction,Mannich reaction,Strecker reaction,and hydrophosphonylation.This strategy has been successfully applied to the synthesis of numerous structurally diverse and multifunctionalized molecules,featuring challenging stereogenic centers.This minireview specifically highlights the accomplishments in asymmetric nucleophilic addition facilitated by chiral quaternary phosphonium catalysts.Its purpose is to cultivate interest among researchers,encouraging more engagement in this field and establishing quaternary phosphonium ion-pair catalysis as a potent and dependable tool for synthetic and pharmaceutical chemists.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41672169, 41473120 & 41502171)the Youth Innovation Promotion Association of Chinese Academy of Sciences (Grant No. 2012295)
文摘Hydroclimatic variations over the eastern Central Asia are highly sensitive to changes in hemispheric-scale atmospheric circulation systems. To fully understand the long-term variability and relationship between hydroclimate and atmospheric circulation system, we present a high-resolution lascustrine record of late Holocene hydroclimate from Lake Sayram, Central Tianshan Mountains, China, based on the total organic carbon, total nitrogen, and carbonate contents, carbon/nitrogen ratios, and grain size. Our results reveal four periods of substantially increased precipitation at the interval of 4000–3780, 3590–3210, 2800–2160, and 890–280 cal yr BP, and one period of slightly increased precipitation from 1700–1370 cal yr BP. These wetter periods broadly coincide with those identified in other records from the mid-latitude Westerlies-dominated eastern Central Asia, including the northern Tibetan Plateau. As such, a similar hydroclimatic pattern existed over this entire region during the late Holocene. Based on a close similarity of our record with reconstruction of North Atlantic Oscillation indices and solar irradiance, we propose that decreased solar irradiance and southern migration of the entire circum-North Atlantic circulation system, particularly the main pathway of the mid-latitude Westerlies, significantly influenced hydroclimate in eastern Central Asia during the late Holocene. Finally, the inferred precipitation at Lake Sayram has increased markedly over the past 100 years, although this potential future changes in hydroclimate in Central Asia need for further investigation.
基金supported by the Shaanxi Science Fund for Distinguished Young Scholars (2018JC-023)the National Natural Science Foundation of China (41842053)+1 种基金the Youth Innovation Promotion Association (2012295)International Partnership Program (132B61KYSB20170005) of Chinese Academy of Sciences
文摘Since Homo sapiens appeared,the planet has experienced continuing environmental changes[1,2].In 2000,Crutzen and Stoermer[3]systematically analysed the global changes caused by human activity over the previous 300 years and suggested that the Holocene epoch ended in the 1750s and a new geological age,the Anthropocene,began.Afterwards,the Anthropocene drew a lot of attention from both scientific community and the general public.The recognition and placement of the Anthropocene/Holocene boundary has been a subject of heated debates over the past two decades.At the 35th International Geological Congress(2016;IGC),the Anthropocene Working Group(AWG)recommended the Anthropocene to be formalised with an epoch rank,with the 1950s as its lower boundary[4].
基金supported by the National Natural Science Foundation of China(Grant No.41991252)the Strategic Priority Research Program(Grant No.XDB40000000)+4 种基金the International Partnership Program(Grant No.132B61KYSB20170005)of Chinese Academy of Sciencesthe National Natural Science Foundation of China(Grant No.41888101)partly supported by the USA National Science Foundation(Grant Nos.0908792,1211299&1702816 to R.Lawrence EDWARDS and Hai CHENG)the 111 Program of China(Grant No.D19002)the Belt&Road Center for Climate and Environment Studies of IEECAS。
文摘Evaluating anthropogenic impacts on regional vegetation changes during historical time is not only important for a better understanding of the Anthropocene but also valuable in improving the vegetation-climate models.In this study,we analyzed stable isotopes(δ^18O,δ^13C)and trace elements(Mg/Ca,Sr/Ca)of a stalagmite from Huangchao Cave in central Shandong,northern China.230Th and AMS14C dating results indicate the stalagmite deposited during 174BC and AD1810,with a hiatus between AD638 and 1102.Broad similarities of theδ^18O and trace elements in the stalagmite suggest they are reliable precipitation indexes.Theδ^13C of the stalagmite,a proxy of vegetation change,was generally consistent with local precipitation and temperature variations on a centennial-scale before the 15th century.It typically varied from–9.6‰to–6.3‰,indicating climate controlled C3 type vegetation during this period.However,a persistent and marked increasing trend in theδ^13C record was observed since the 15th century,resulting inδ^13C values from–7.7‰to–1.6‰in the next four centuries.This unprecedentedδ^13C change caused by vegetation deterioration cannot be explained by climate change but is fairly consistent with the dramatically increasing population and farmland in Shandong.We suggest that the increasing deforestation and reclamation in central Shandong began to affect vegetation in the mountain region of central Shandong since the 15th century and severely destroyed or even cleared the forest during the 16th–18th century.
基金supported by the National Natural Science Foundation of China(21971165,21921002)the National Key R&D Program of China(2018YFA0903500)+3 种基金the“1000-Youth Talents Program”(YJ201702)the Fundamental Research Funds from Sichuan University(2020SCUNL108)Beijing National Laboratory for Molecular Sciences(BNLMS202101)the Fundamental Research Funds for the Central Universities。
文摘Stereodivergently constructing the designed products having adjacent multi-stereocenters via a given reaction,with excellent control of both absolute and relative configurations,presents one of the substantial hurdles in asymmetric catalysis.Herein,we report a precisely stereodivergent asymmetric protocol by synergistic combination of phosphonium-involved ion-pair catalysis and base for accessing to chiral phosphorus compounds bearing two adjacent chiral centers particularly containing an acidic protonated enantioenriched carbon atom,having broad functional group compatibility in both dynamic and thermodynamic processes under mild reaction conditions.Two keys for the success in constructing these stereoisomers with high levels of regio-,diastereo-,and enantioselectivities were contained:firstly,the precise stereo-control in providing dynamic products was enabled by bifunctional phosphonium salt catalyst with semi-enclosed cavity;secondly,the readily stereospecific transformation of adducts from dynamic to thermodynamic version was initiated by achiral base.All four stereoisomers could be readily accessed even in gram-scale in high yields with maintaining excellent stereoselectivities,illustrating the potential of this synergistic catalytic methodology in organic synthesis.Moreover,mechanistic studies including density functional theory(DFT)calculations and control experiments provide insights into the mechanism.
基金supported by the National Natural Science Foundation of China(21971165,21921002,81630101)the National Key Research and Development Program of China(2018YFA0903500)+1 种基金the“1000-Youth Talents Program”(YJ201702)the Fundamental Research Funds for the Central Universities。
文摘Structurally fused heterocycles encompassing a centerpiece of benzotropane are significant scaffolds with a plethora of promising biological activities,but such molecular architectures pose a long-standing daunting synthetic challenge.Herein,we reported a highly efficient asymmetric cyclodearomatization of 2-nitrobenzofurans with cyclic azomethine ylides by employing bifunctional phosphonium salts as phase-transfer catalysts.Under optimized reaction conditions,a diverse array of polycyclic benzofused tropane derivatives with four contiguous 4°/3°stereocenters were readily synthesized in both high yields and diastereoselectivities with up to>99%ee.The practicality and utility of this protocol were further demonstrated by the scaled-up reaction and facile elaborations.Moreover,preliminary investigations into their antitumor activities were also presented.
基金support was provided by the National Natural Science Foundation of China(21971165,21921002,21772035,22101189)National Key R&D Program of China(2018YFA0903500)National Natural Science Foundation of Hunan(2021JJ40150).
文摘We present a phosphonium-containing catalyst generated in situ from phosphine and tert-butyl acrylate that serves as an unusual Lewis base catalyst.It was applied for the promotion of a remote 1,6-cyanation reaction of p-quinone methides and fuchsones employing trimethylsilyl cyanide as the cyanide source.A diverse range ofα-diaryl andα-triaryl acetonitriles was obtained in high yields under mild reaction conditions with low catalyst loading(5 mol%).The practicality and utility of this protocol were demonstrated via the gram-scale preparation and facile elaboration of products.Mechanistic investigations(in situ NMR and ESI-MS analysis)were employed to characterize the active zwitterionic phosphonium intermediate,which was the“true”active catalyst.