Synthesis of Biheteroaryls by Pd-Catalyzed Homocoupling of Heteroaryl Bromides.

Symmetrical biheteroaryl compounds, such as bypyridines and bipyrazoles, are important ligands in transition-metal catalysis. They also serve as synthetic precursors of photo catalysts/sensitizers, bioactive agents, and energetic materials. To facilitate the concise synthesis of these useful structures, an efficient Pd-catalyzed homocoupling of heteroaryl bromides has been successfully established using the electron-rich and sterically hindered monophosphorus ligand BIDIME.

Heck Reaction of N-Heteroaryl Halides for the Concise Synthesis of Chiral α-Heteroaryl-substituted Heterocycles.

The Heck reaction between N-heteroaryl halides and heterocyclic alkenes provides a convenient approach to biologically relevant α-heteroaryl functionalized heterocycles, yet reactions of this type have been challenging due to strong N-heteroaryl coordination to palladium metal, which causes catalyst poisoning. In this report, an efficient palladium-catalyzed Heck reaction between N-heteroaryl halides and heterocyclic olefins is established, leading to a variety of α-heteroaryl substituted heterocycles. The method features an unprecedented broad substrate scope and excellent functional group compatibility.

Synthesis of α-Heteroaryl Propionic Esters by Palladium-Catalyzed α-Heteroarylation of Silyl Ketene Acetals.

A practical and efficient synthesis of α-heteroaryl propionic esters is developed by employing palladium-catalyzed α-heteroarylation of silyl ketene acetals, forming a wide variety of α-heteroaryl propionic esters with various substituents and functionalities in high yields. The success of this transformation is credited to the development of the bulky P,P═O ligand. The method has provided an efficient synthesis of α-heteroaryl propionic acids.

Fish isotopic niches associated with environmental indicators and human disturbance along a disturbed large subtropical river in China.

Stable isotopes are increasingly used to detect and understand the impacts of environmental changes on riverine ecological properties. The δC and δN signatures of fish with different feeding habits were measured in a large subtropical river to evaluate how fish isotopic niches respond to environmental gradients and human disturbance. From basal resources to fish consumers, the high values of epilithic periphyton (biofilm) δC and suspended particulate organic matter δN concurrently determined the niche ranges and space (e.

Stable isotopes reveal effects of natural drivers and anthropogenic pressures on isotopic niches of invertebrate communities in a large subtropical river of China.

Isotopic niches reflect the basic structure and functioning of river food webs; however, their response to riverine environments remains unclear. We used stable isotope analysis and community-wide metrics to quantify how invertebrate niches vary with environmental changes along a large subtropical river in China. Eight niche metrics, which had higher values in the wet than in the dry season, increased from headwaters to the middle river and decreased sharply near the estuarine industrial zones.

Evaluation of factors influencing annual occurrence, bioaccumulation, and biomagnification of antibiotics in planktonic food webs of a large subtropical river in South China.

Biological pump is important to control the fate and distribution of organic contaminants, particularly in temperate and cold oligotrophic waters. However, it remains largely unknown how factors affect the long-term occurrence and fate of ionogenic organic compounds in subtropical eutrophic waters. The present study aimed to assess biogeochemical and physical factors affecting the annual occurrence, bioaccumulation, and trophic transfer of 14 antibiotics through planktonic food webs in the Pearl River, a large subtropical eutrophic river in China.