A stereocontrolled construction of the side chain of brassinclide and homobrassinolide has been achieved via the tandem vicinal dialkylation of the pyranone moiety as a key step.
The scope of stereochemistry recognition usually occurs near the chiral scaffold of a ligand or catalyst.Remote stereocontrol,which can surpass the limits of stereorecognition of remote prochiral centers,has long been...The scope of stereochemistry recognition usually occurs near the chiral scaffold of a ligand or catalyst.Remote stereocontrol,which can surpass the limits of stereorecognition of remote prochiral centers,has long been a challenging object of great interest in asymmetric catalysis.The current work realized the remote stereocontrol of 1,7-zwitterion intermediates formed from Huang's o-amino aryl MBH carbonates.With simple and easily accessibleβ-ICD as the bifunctional catalyst,multifunctionalized tetrahydroquinoline derivatives could be synthesized via(4+2)cycloadditions with excellent enantioselectivity and diastereoselectivity under mild conditions.The strategy possesses broad substrate scope,and three types of electron-deficient enones are successfully applied.Mechanistic studies disclosed the Lewis base-catalyzed reaction pathway,and H-bonding between the catalyst and enones is crucial for long-range stereocontrol.Scale-up reaction and transformations of the tetrahydroquinoline products demonstrated the potential of this strategy.展开更多
The radical polymerization of methyl methacrylate(MMA) was carried out in the presence of combined Lewis acids of the AlCl3-FeCl2 system.Compared with the polymerization produced in the presence of single Lewis acids,...The radical polymerization of methyl methacrylate(MMA) was carried out in the presence of combined Lewis acids of the AlCl3-FeCl2 system.Compared with the polymerization produced in the presence of single Lewis acids,AlCl3 or FeCl2,the MMA polymerization in the presence of AlCl3-FeCl2 composite in CHCl3 or 1-butanol produced a polymer with a higher isotacticity and in toluene produced a polymer with a much higher isotacticity(mm=50%) .The molecular weight and polydispersity of PMMA in the presence of Lewis acids were similar with those in the absence of Lewis acids,although Lewis acids decelerate the polymerization of MMA.The effects of the Lewis acids were greater in a solvent with a lower polarity.A possible stereocontrol mechanism of the polymerization was proposed.The Lewis acid composite of AlCl3-FeCl2 readily formed a complex with growing species.These complexes possessed apparent bulkiness that changes the direction of monomer addition to the growing radical center.展开更多
Asymmetric olefin isomerization has become a powerful tool for positional migration of C=C double bonds to afford valuable chiral olefins.However,the synthesis of optically active all-carbon quaternary stereocenters v...Asymmetric olefin isomerization has become a powerful tool for positional migration of C=C double bonds to afford valuable chiral olefins.However,the synthesis of optically active all-carbon quaternary stereocenters via this strategy is still rare.Herein,we report a cobaltcatalyzed desymmetric olefin isomerization to access 1-methylcyclohexenes bearingβ-quaternary stereocenters in a chemo-,site-,and stereoselective fashion.Preliminary mechanistic studies have revealed the Co-H insertion/β–Helimination reaction pathway and the origin of remote stereocontrol of all-carbon quaternary centers.The gram-scale synthesis and stereoretentive transformations of spirocyclic products demonstrate the synthetic utility of this reaction.展开更多
In contrast to the stereocontrol of the stereocenter at the allyl unit,the asymmetric induction of prochiral nucleophiles remains a challenge in Pd-catalyzed asymmetric allylic substitutions due to the remote distance...In contrast to the stereocontrol of the stereocenter at the allyl unit,the asymmetric induction of prochiral nucleophiles remains a challenge in Pd-catalyzed asymmetric allylic substitutions due to the remote distance between the chiral catalyst and the stereocenter established at prochiral nucleophile.Much effort has been devoted to solving this challenge through the elaborate design of chiral ligands.Recently,synergistic catalysis has gained increasing attention owing to its potential advantages over the traditional single palladium catalysis,such as improvement of reactivity and selectivity.This strategy,including bimetallic catalysis and Pd/organocatalysis,not only broadens the scope of prochiral nucleophiles,but also provides a simple and unified method for the stereocontrol of prochiral nucleophiles.This review summarizes the brief history and advances in this field.展开更多
Stereocontrolled synthesis of 3(R) and 3(S)-hydroxyeicos-4(E)-en-1-yne has been achieved through double elimination of chloride intermediates 8 and 11, which were prepared from acetylenic alcohol intermediates 1 and 10.
文摘A stereocontrolled construction of the side chain of brassinclide and homobrassinolide has been achieved via the tandem vicinal dialkylation of the pyranone moiety as a key step.
基金the National Natural Science Foundation of China(Nos.82073997 and 22001024)the Science&Technology Department of Sichuan Province(Nos.2021YFS0044 and 2021YJ0402)+1 种基金Innovation Team and Talents Cultivation Program of National Administration of Traditional Chinese Medicine(No.ZYYCXTD-D-202209)Xinglin Scholar Research Promotion Project of Chengdu University of TCM.
文摘The scope of stereochemistry recognition usually occurs near the chiral scaffold of a ligand or catalyst.Remote stereocontrol,which can surpass the limits of stereorecognition of remote prochiral centers,has long been a challenging object of great interest in asymmetric catalysis.The current work realized the remote stereocontrol of 1,7-zwitterion intermediates formed from Huang's o-amino aryl MBH carbonates.With simple and easily accessibleβ-ICD as the bifunctional catalyst,multifunctionalized tetrahydroquinoline derivatives could be synthesized via(4+2)cycloadditions with excellent enantioselectivity and diastereoselectivity under mild conditions.The strategy possesses broad substrate scope,and three types of electron-deficient enones are successfully applied.Mechanistic studies disclosed the Lewis base-catalyzed reaction pathway,and H-bonding between the catalyst and enones is crucial for long-range stereocontrol.Scale-up reaction and transformations of the tetrahydroquinoline products demonstrated the potential of this strategy.
文摘The radical polymerization of methyl methacrylate(MMA) was carried out in the presence of combined Lewis acids of the AlCl3-FeCl2 system.Compared with the polymerization produced in the presence of single Lewis acids,AlCl3 or FeCl2,the MMA polymerization in the presence of AlCl3-FeCl2 composite in CHCl3 or 1-butanol produced a polymer with a higher isotacticity and in toluene produced a polymer with a much higher isotacticity(mm=50%) .The molecular weight and polydispersity of PMMA in the presence of Lewis acids were similar with those in the absence of Lewis acids,although Lewis acids decelerate the polymerization of MMA.The effects of the Lewis acids were greater in a solvent with a lower polarity.A possible stereocontrol mechanism of the polymerization was proposed.The Lewis acid composite of AlCl3-FeCl2 readily formed a complex with growing species.These complexes possessed apparent bulkiness that changes the direction of monomer addition to the growing radical center.
基金We gratefully acknowledge funding from the National Key R&D Program of China(grant no.2021YFF0701600)the National Natural Science Foundation of China(grant nos.22171159 and 22225103).
文摘Asymmetric olefin isomerization has become a powerful tool for positional migration of C=C double bonds to afford valuable chiral olefins.However,the synthesis of optically active all-carbon quaternary stereocenters via this strategy is still rare.Herein,we report a cobaltcatalyzed desymmetric olefin isomerization to access 1-methylcyclohexenes bearingβ-quaternary stereocenters in a chemo-,site-,and stereoselective fashion.Preliminary mechanistic studies have revealed the Co-H insertion/β–Helimination reaction pathway and the origin of remote stereocontrol of all-carbon quaternary centers.The gram-scale synthesis and stereoretentive transformations of spirocyclic products demonstrate the synthetic utility of this reaction.
基金supported by the National Natural Science Foundation of China(21831005,21991112,22171183)the Science and Technology Commission of Shanghai Municipality(19JC1430100)。
文摘In contrast to the stereocontrol of the stereocenter at the allyl unit,the asymmetric induction of prochiral nucleophiles remains a challenge in Pd-catalyzed asymmetric allylic substitutions due to the remote distance between the chiral catalyst and the stereocenter established at prochiral nucleophile.Much effort has been devoted to solving this challenge through the elaborate design of chiral ligands.Recently,synergistic catalysis has gained increasing attention owing to its potential advantages over the traditional single palladium catalysis,such as improvement of reactivity and selectivity.This strategy,including bimetallic catalysis and Pd/organocatalysis,not only broadens the scope of prochiral nucleophiles,but also provides a simple and unified method for the stereocontrol of prochiral nucleophiles.This review summarizes the brief history and advances in this field.
文摘Stereocontrolled synthesis of 3(R) and 3(S)-hydroxyeicos-4(E)-en-1-yne has been achieved through double elimination of chloride intermediates 8 and 11, which were prepared from acetylenic alcohol intermediates 1 and 10.
