Search

Comprehensive Summary: Axially chiral biaryls represent the most important class of atropisomers, and they widely exist in natural products and biologically active molecules. They also constitute a unique scaffold for chiral ligands and catalysts in organic synthesis. The development of synthetic methods to obtain such chiral compounds has received widespread attention, among which catalytically atroposelective ring‐opening of configurationally labile compounds represents one of the most attractive strategies. Various substrates with strained cyclic structures, such as the renowned Bringmann's lactones, can undergo asymmetric transformation into stable atropisomers. Known advancement primarily relies on metal catalyst combined with well‐designed chiral ligands, the approaches utilizing organocatalysis as a critical resolution strategy are notably scarce. In this study, we disclosed a N‐heterocyclic carbene (NHC)‐catalyzed asymmetric ring‐opening reaction of biaryl lactams via direct atroposelective nucleophilic activation. The optimized bulky carbene catalyst ensures that the reaction can proceed under mild conditions, affording the desired product with good to excellent yields and atroposelectivity. [ABSTRACT FROM AUTHOR]

Climate change accelerates the global water cycle. However, the relationships between climate change and hydrological processes in the alpine arid regions remain elusive. We sampled surface water and groundwater at high spatial and temporal resolutions to investigate these relationships in the Qaidam Basin, an extremely arid area in the northeastern Tibetan Plateau. Stable H–O isotopes and radioactive 3 H isotopes were combined with atmospheric simulations to examine hydrological processes and their response mechanisms to climate change. Contemporary climate processes and change dominate the spatial and temporal variations of surface water isotopes, specifically the westerlies moisture transport and the local temperature and precipitation regimes. The H–O isotopic compositions in the eastern Kunlun Mountains showed a gradually depleted eastward pattern, while a reverse pattern occurred in the Qilian Mountains water system. Precipitation contributed significantly more to river discharge in the eastern basin (approximately 45 %) than in the middle and western basins (10 %–15 %). Moreover, increasing precipitation and a shrinking cryosphere caused by current climate change have accelerated basin groundwater circulation. In the eastern and southwestern Qaidam Basin, precipitation and meltwater infiltrate along preferential flow paths, such as faults, volcanic channels, and fissures, permitting rapid seasonal groundwater recharge and enhanced terrestrial water storage. However, compensating for water loss due to long-term ice and snow melt will be a challenge under projected increasing precipitation in the southwestern Qaidam Basin, and the total water storage may show a trend of increasing before decreasing. Great uncertainty about water is a potential climate change risk facing the arid Qaidam Basin. [ABSTRACT FROM AUTHOR]

In cold alpine regions, ecohydrological feedback to climatic anomalies can provide valuable insights into ecosystem functions in the context of alarming climate change projections. However, the role of vegetation in the hydrological cycle of alpine wetlands remains unclear. We used water stable isotopes (δ18O and δD) supplemented with δ13C to investigate wetland soil isotope distributions and plant water uptake patterns. The isotope values of the soil profiles were affected by seasonal factors. During cold and dry periods, the isotopes within the soil profile showed a strong evaporation effect, and during warm and humid periods, the isotopes indicated the mixing of multiple water sources. The isotopes show larger variations in the interior of the wetland than in the periphery. The carbon dioxide and methane released by the wetland may cause a negative shift in the δ18O and δD isotopes of soil water. Rose willow and Sophora moorcroftiana can obtain water from both the surface and deep layers to cope with different water stresses. The dominant water is mainly obtained from the surface layer during cold and dry periods, whereas water from deeper layers can also be abstracted during warm and wet periods for rose willow growth. These findings will provide a better understanding of soil and plant water hydrological cycles under harsh natural conditions in cold alpine regions and could offer guidance to local governments for the conservation of this extreme wetland ecosystem. [ABSTRACT FROM AUTHOR]