Conspectus Ynamides are electron-rich heteroatom-substituted alkynes with a C–C triple bond directly attached to the amide group. Importantly, this amide group is able to impose an electronic bias, ...thus resulting in the highly regioselective attack of this polarized alkyne by a large variety of nucleophiles. Over the past two decades, catalytic reactions of ynamides have experienced dramatic developments, especially those catalyzed by transition metals. As a result, ynamides have been widely applied to the rapid and efficient assembly of versatile structurally complex N-containing molecules, especially in an atom-economic and stereoselective way. On the basis of newly developed ynamide preparations and new alkyne transformations, we first developed oxidation-initiated tandem reactions of ynamides such as zinc-catalyzed ynamide oxidation/C–H functionalization and copper-catalyzed ynamide oxidation/carbene metathesis, leading to divergent synthesis of isoquinolones, β-carbolines, and pyrrolo3,4-cquinolin-1-ones. Importantly, this protocol represents the first non-noble-metal-catalyzed intermolecular oxidation of alkynes by N-oxide type oxidants, and the related overoxidation could be dramatically inhibited in this non-noble-metal catalysis. Then, we achieved gold-catalyzed amination-initiated tandem reactions of ynamides via α-imino gold carbenes for efficient construction of various 2-aminoindoles, 3-amino-β-carbolines, and 2-aminopyrroles, where two new types of nitrene transfer reagents (benzyl azides and isoxazoles) were discovered. In particular, the use of isoxazoles as nitrene transfer reagents for atom-economic generation of α-imino metal carbenes has also been elegantly exploited by Hashmi, Liu, and many other groups, providing ready access to a wide range of functionalized N-heterocycles. Moreover, we revealed that donor/donor copper carbenes could be generated via copper-catalyzed diyne cyclization under mild conditions. These novel copper carbenes could undergo asymmetric C–H insertion, cyclopropanation, and formal 3 + 2 cycloaddition to produce diverse chiral polycyclic pyrroles with good to excellent enantioselectivities. Thus, this strategy may open new avenues in catalytic asymmetric reaction of ynamides, which remain largely unexplored and deserve more attention. Meanwhile, we also accomplished the efficient and practical synthesis of medium-sized lactams by yttrium-catalyzed cascade cyclization of allyl alcohol-tethered ynamides and the combination of radical chemistry based on visible-light photoredox catalysis with ynamide chemistry for divergent synthesis of useful 2-benzhydrylindoles and 3-benzhydrylisoquinolines. In this Account, we describe a panoramic picture of our recent contributions since 2015 to the development and application of ynamide chemistry in organic synthesis via transition metal-catalyzed tandem reactions by focusing on the tetrafunctionalization of ynamides. These studies provide not only efficient and attractive methods for divergent synthesis of valuable N-heterocycles but also some new insights into the exploration of alkyne chemistry and metal carbene chemistry.
This study examines potential future changes of precipitation in China based on Coupled Model Intercomparison Project Phase 5 (CMIP5) climate model projections for the medium (RCP4.5) and high ...(RCP8.5) emission scenarios. We first evaluate the biases of climate model output and correct the biases through quantile mapping. After bias correction, we examine the changes in mean precipitation as well as shifts in its frequency distribution. We also evaluate the changes in extreme precipitation based on frequency analysis techniques. Our results show that by the end of the century, mean precipitation is going to increase by 8% (12%) under RCP4.5 (RCP8.5) scenarios, resulted from a combination of an increase in precipitation intensity and a slight decrease in precipitation frequency. Spatially, precipitation is projected to increase more in northern China than southern China, and the increase is the least in the southeast. Seasonally, precipitation is projected to increase more in fall and winter, and less in spring and summer. The precipitation intensity distribution is likely to shift towards more heavy events, with a decrease in the contribution from light events and a significant increase in contribution from heavy events. Extreme precipitation is going to increase at much higher rates than mean precipitation, and the increase is more spatially uniform. Changes in annual and seasonal precipitation are closely linked with temperature change. Total precipitation increases at 2.6% (1.9%) per degree warming under RCP4.5 (RCP8.5), but extreme precipitation has much higher sensitivities ranging 4.5–6.5% per degree warming for events of various return intervals. The percentage increase per degree is generally smaller for RCP8.5 than RCP4.5 scenarios, suggesting a reduced sensitivity at higher temperature. In addition, the precipitation increase seems to be linked with changes in the atmospheric circulations that transport moisture in different regions in China. These changes have significant implications for the management of water resources and water‐related hazards.
This figure shows the projected percentage change between 1971–2000 and 2071–2100 under the medium (RCP4.5) and high (RCP8.5) climate change scenarios for precipitation mean, frequency, and intensity in China. It shows a general increase in precipitation and decrease in frequency, leading to a greater increase in precipitation intensity. The frequency distribution is going to shift towards more intense precipitation, with an even greater increase for extreme precipitation.
Landscape planning and design is an indispensable part of modern urban construction. In landscape design, rendering technology can transform designers' imagination into actual images, allowing people ...to better understand the design intent. In order to solve the problem of insufficient precision in image rendering in landscape design, this paper proposes a landscape design image rendering technology based on improved neural network technology. This technology combines stereo matching algorithms, which evaluate the corrected stereo images to calculate the differences between the real scene and the underlying model. The stereo matching algorithm is based on the basic model and obtains accurate depth information from a wide range image pair, making the rendered landscape image more realistic and precise. The experiment demonstrates the effectiveness of the landscape design image rendering system through two important aspects: processing speed and parallax accuracy. The development of image rendering technology in landscape design cannot be separated from the mutual promotion of theory and practice. The technology proposed in this article has certain practical value and hopes to make more positive contributions to urban construction and cultural inheritance.
Recently, Kovalenko and co‐workers and Li and co‐workers developed CsPbX3 (X = Cl, Br, I) inorganic perovskite quantum dots (IPQDs), which exhibited ultrahigh photoluminescence (PL) quantum yields ...(QYs), low‐threshold lasing, and multicolor electroluminescence. However, the usual synthesis needs high temperature, inert gas protection, and localized injection operation, which are severely against applications. Moreover, the so unexpectedly high QYs are very confusing. Here, for the first time, the IPQDs' room‐temperature (RT) synthesis, superior PL, underlying origins and potentials in lighting and displays are reported. The synthesis is designed according to supersaturated recrystallization (SR), which is operated at RT, within few seconds, free from inert gas and injection operation. Although formed at RT, IPQDs' PLs have QYs of 80%, 95%, 70%, and FWHMs of 35, 20, and 18 nm for red, green, and blue emissions. As to the origins, the observed 40 meV exciton binding energy, halogen self‐passivation effect, and CsPbX3@X quantum‐well band alignment are proposed to guarantee the excitons generation and high‐rate radiative recombination at RT. Moreover, such superior optical merits endow them with promising potentials in lighting and displays, which are primarily demonstrated by the white light‐emitting diodes with tunable color temperature and wide color gamut.
A room‐temperature supersaturated recrystallization method is developed to rapidly synthesize all‐inorganic halide perovskite QDs with blue, green, and red luminescent quantum yields of 70%–95% and line‐widths less than 35 nm. The origins of the optical superiority are proposed to be the observed 40 meV exciton binding energy, surface self‐passivation effect, and quantum‐well band alignment. Such superior optical merits endow them with promising potentials in healthy lighting and wide‐color‐gamut displays, which are primarily demonstrated by the color‐temperature‐tunable white light‐emitting diodes.
Described herein is an organocatalytic enantioselective desymmetrizing cycloisomerization of arylsulfonyl‐protected ynamide cyclohexanones, representing the first metal‐free asymmetric Conia‐ene‐type ...carbocyclization. This method allows the highly efficient and atom‐economical construction of a range of valuable morphans with wide substrate scope and excellent enantioselectivity (up to 97 % ee). In addition, such a cycloisomerization of alkylsulfonyl‐protected ynamide cyclohexanones can lead to the divergent synthesis of normorphans as the main products with high enantioselectivity (up to 90 % ee). Moreover, theoretical calculations are employed to elucidate the origins of regioselectivity and enantioselectivity.
An organocatalytic enantioselective desymmetrizing cycloisomerization of arylsulfonyl‐protected ynamide cyclohexanones is disclosed for practical and atom‐economical assembly of morphans with excellent enantioselectivities. It represents the first metal‐free asymmetric Conia‐ene‐type carbocyclization. In addition, cycloisomerization of the alkylsulfonyl‐protected ynamide cyclohexanones leads to normorphans with high enantioselectivities.
Gold-catalyzed intermolecular alkyne oxidation by an N-O bond oxidant has proven to be a powerful method in organic synthesis during the past decade, because this approach would enable readily ...available alkynes as precursors in generating α-oxo gold carbenes. Among those, gold-catalyzed oxidative cyclization of dialkynes has received particular attention as this chemistry offers great potential to build structurally complex cyclic molecules. However, these alkyne oxidations have been mostly limited to noble metal catalysts, and, to our knowledge, non-noble metal-catalyzed reactions such as diyne oxidations have not been reported. Herein, we disclose a copper-catalyzed oxidative diyne cyclization, allowing the facile synthesis of a wide range of valuable pyrrolo3,4-cquinolin-1-ones. Interestingly, by employing the same starting materials, the gold-catalyzed cascade cyclization leads to the divergent formation of synthetically useful pyrrolo2,3-bindoles. Furthermore, the proposed mechanistic rationale for these cascade reactions is strongly supported by both control experiments and theoretical calculations.
In recent years, asymmetric catalysis of ynamides has attracted much attention, but these reactions mostly constructed central chirality, except for a few examples on the synthesis of axially chiral ...compounds which exclusively relied on noble‐metal catalysis. Herein, a facile access to axially chiral N‐heterocycles enabled by chiral Brønsted acid‐catalyzed 5‐endo‐dig cyclization of ynamides is disclosed, which represents the first metal‐free protocol for the construction of axially chiral compounds from ynamides. This method allows the practical and atom‐economical synthesis of valuable N‐arylindoles in excellent yields with generally excellent enantioselectivities. Moreover, organocatalysts and ligands based on such axially chiral N‐arylindole skeletons are demonstrated to be applicable to asymmetric catalysis.
A chiral Brønsted acid‐catalyzed atroposelective cyclization of ynamides is disclosed, which represents the first metal‐free protocol for the construction of axially chiral compounds from ynamides. This method enables the practical and atom‐economical synthesis of valuable N‐arylindoles in excellent yields with generally excellent enantioselectivities.
•δ18O, δ2H, and d-excess of groundwater and stream show spatial variation.•This study presents the first groundwater and stream isoscape of Ethiopia.•The isotopic composition of groundwater is biased ...towards the wet season isotopes in precipitation.•High-intensity storms are an important source of groundwater recharge.
Sustainable water resource management requires a clear understanding of the spatial variation and seasonal recharge of groundwater and their links to local precipitation. A combined spatial analysis of the stable isotope composition of groundwater, surface water, and precipitation could help to understand groundwater sources and recharge processes. In this study, we collected 297 groundwater and stream water samples across Ethiopia and analyzed them for the oxygen and hydrogen isotope ratios. The isotope data were then interpolated into isoscapes for the entire country using the Cokriging method based on their spatial autocorrelation and covariance with elevation, annual mean precipitation, and temperature. These are the first groundwater and stream isoscapes for Ethiopia. By comparing the spatial isotopic distribution of the two water resources with local precipitation, we showed distinct groundwater recharge patterns in different regions in terms of their water sources, timing, seasonality, and the degree of surface and groundwater interaction. We found that the groundwater recharge was generally biased towards the main rainy season. However, in the relatively dry southeastern Ethiopia, groundwater could receive significant input from infrequent high-intensity rainfalls associated with tropical cyclones, but additional precipitation and groundwater isotope data are needed to further test our hypothesis in this data-poor region. Overall, this study has largely expanded the spatial coverage of water stable isotope data and filled significant data gaps in Ethiopia, which could be used to provide vital information in the arid and semi-arid parts of the country where water resources are critical in climate change adaptation strategies.
The location, size, and number of synapses critically influence the specificity and strength of neural connections. In axons, synaptic vesicle (SV) and active zone (AZ) proteins are transported by ...molecular motors and accumulate at discrete presynaptic loci. Little is known about the mechanisms coordinating presynaptic protein transport and deposition to achieve proper distribution of synaptic material. Here we show that SV and AZ proteins exhibit extensive cotransport and undergo frequent pauses. At the axonal and synaptic pause sites, the balance between the capture and dissociation of mobile transport packets determines the extent of presynaptic assembly. The small G protein ARL-8 inhibits assembly by promoting dissociation, while a JNK kinase pathway and AZ assembly proteins inhibit dissociation. Furthermore, ARL-8 directly binds to the UNC-104/KIF1A motor to limit the capture efficiency. Together, molecular regulation of the dichotomy between axonal trafficking and local assembly controls vital aspects of synapse formation and maintenance.
•The balance between transport and assembly controls synapse distribution•ARL-8 and a JNK pathway antagonistically regulate presynaptic protein dissociation•AZ proteins are cotransported with STVs and promote STV clustering during transport•UNC-104/KIF1A functions as an ARL-8 effector to regulate presynaptic cargo capture
Wu et al. report that a molecular network composed of the small G protein ARL-8, the JNK kinase pathway, active zone proteins, and the UNC-104/KIF1A motor regulates the balance between presynaptic protein transport and assembly to control synapse distribution.
Stable isotopes of oxygen (δ18O) and hydrogen (δD) in precipitation can be used as dual conservative tracers in the hydrologic cycle and help to understand hydrological and atmospheric processes. ...Although long-term monthly precipitation global isotope datasets are available in some locations, currently there are limited daily precipitation isotope data, particularly in the Midwest region of the USA. In this study we report a daily precipitation δ18O and δD dataset from March 2014–December 2017 in Dayton, Ohio, the USA. The daily δ18O and δD vary from −28.0 to 0.4‰, and −214.0 to 9.0‰ respectively. The data exhibit strong seasonality with lower δ18O and δD values in the winter and higher values in the summer. The precipitation isotopic values are mainly controlled by temperature, and show no correlation with precipitation amount and relative humidity. However, δ18O-temperature relationship varies among different seasons. The correlation is the strongest in winter (R2 = 0.56), weaker in spring (R2 = 0.28) and fall (R2 = 0.24), and almost non-existent in summer (R2 = 0.1). The slope values also vary with highest value in winter (0.68‰/OC) and much smaller in other seasons. The HYSPLIT back trajectory analyses show that Pacific, Gulf of Mexico, Arctic and Continental moistures are the main sources for southwestern Ohio with different seasonal contributions. The isotopic compositions of precipitation from different sources show small intra-season variations but large seasonal variability. Our daily-resolved dataset provides new insights into the main controls on the isotopic composition of precipitation and its seasonal variations, which could help to understand atmospheric processes and enable their proper use in interpretation of paleoclimate proxies, particularly those with seasonal bias.
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•δ18O shows seasonality with high values in the summer and low values in the winter.•Precipitation isotopic composition is mainly controlled by temperature.•The δ18O-T relationship varies seasonally with highest slope in winter.•Dayton gets moisture from Pacific, Gulf of Mexico, Arctic and Continental sources.•δ18O from different sources are similar within a season but vary seasonally.
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