Concise synthesis of eight-membered lactones,a kind of medium-sized heterocycles widespread in many bioactive natural products,is highly significant.However,it still remains a challenge due to unfavorable entropic fac...Concise synthesis of eight-membered lactones,a kind of medium-sized heterocycles widespread in many bioactive natural products,is highly significant.However,it still remains a challenge due to unfavorable entropic factor and transannular interaction.Herein,we disclose an enantioselective synthesis of eight-membered lactones through a Pd-catalyzed asymmetric(6+2)dipolar annulation of vinyl oxetanes andα-diazo ketones(20 examples,up to 93%yield and 95:5 er).This reaction features simple operation,mild conditions and good enantiocontrol,especially the challenging chiral all-carbon quaternary stereocenter.A newly developed chiral hybrid P,S ligand and the in-situ photo-generation of ketene dipolarophiles are crucial to this success.展开更多
The metallic glass matrix composites（MGMCs）and bulk metallic glasses（BMGs）were studied by statistical analysis during plastic deformation at the strain rates of 2×10^-2,2×10^-3,and 2×10^-4 s^-1,resp...The metallic glass matrix composites（MGMCs）and bulk metallic glasses（BMGs）were studied by statistical analysis during plastic deformation at the strain rates of 2×10^-2,2×10^-3,and 2×10^-4 s^-1,respectively.No serration events occur in both MGMCs and BMGs during compression tests at the strain rate of 2×10^-2 s^-1.When deformed at the strain rate of 2×10^-3 s^-1,the BMG displays a larger plasticity,which is due to the larger serration events followed by a series of small serrations caused by the continuous movement of free volume.The amplitudes and elastic-energy densities increase with increasing the strain rates owing to many serrations in MGMCs.It is deduced that the Young′s modulus decreases from the normalized stress drop and fluctuations are observed on stressstrain curves,which is attributed to a lower coefficient according to the stick-slip model.展开更多
基金supported by the National Natural Science Foundation of China(21822103,21820102003,91956201)the Program of Introducing Talents of Discipline to Universities of China(111Program,B17019)+1 种基金the Natural Science Foundation of Hubei Province(2017AHB047)Hubei International Scientific and Technological Cooperation Base of Pesticide and Green Synthesis。
文摘Concise synthesis of eight-membered lactones,a kind of medium-sized heterocycles widespread in many bioactive natural products,is highly significant.However,it still remains a challenge due to unfavorable entropic factor and transannular interaction.Herein,we disclose an enantioselective synthesis of eight-membered lactones through a Pd-catalyzed asymmetric(6+2)dipolar annulation of vinyl oxetanes andα-diazo ketones(20 examples,up to 93%yield and 95:5 er).This reaction features simple operation,mild conditions and good enantiocontrol,especially the challenging chiral all-carbon quaternary stereocenter.A newly developed chiral hybrid P,S ligand and the in-situ photo-generation of ketene dipolarophiles are crucial to this success.
基金Item Sponsored by National Natural Science Foundation of China(51371122,51471025,51210105006)Program for Innovative Talents of Higher Learning Institutions of Shanxi of China(2013)Youth Natural Science Foundation of Shanxi Province of China(2015021005)
文摘The metallic glass matrix composites（MGMCs）and bulk metallic glasses（BMGs）were studied by statistical analysis during plastic deformation at the strain rates of 2×10^-2,2×10^-3,and 2×10^-4 s^-1,respectively.No serration events occur in both MGMCs and BMGs during compression tests at the strain rate of 2×10^-2 s^-1.When deformed at the strain rate of 2×10^-3 s^-1,the BMG displays a larger plasticity,which is due to the larger serration events followed by a series of small serrations caused by the continuous movement of free volume.The amplitudes and elastic-energy densities increase with increasing the strain rates owing to many serrations in MGMCs.It is deduced that the Young′s modulus decreases from the normalized stress drop and fluctuations are observed on stressstrain curves,which is attributed to a lower coefficient according to the stick-slip model.
