Nickel-catalyzed electrophiles-controlled enantioselective reductive arylative cyclization and enantiospecific reductive alkylative cyclization of 1,6-enynes.

Transition metal-catalyzed asymmetric cyclization of 1,6-enynes is a powerful tool for the construction of chiral nitrogen-containing heterocycles. Despite notable achievements, these transformations have been largely limited to the use of aryl or alkenyl metal reagents, and stereoselective or stereospecific alkylative cyclization of 1,6-enynes remains unexploited. Herein, we report Ni-catalyzed enantioselective reductive anti-arylative cyclization of 1,6-enynes with aryl iodides, providing enantioenriched six-membered carbo- and heterocycles in good yields with excellent enantioselectivities. Additionally, we have realized Ni-catalyzed enantiospecific reductive cis-alkylative cyclization of 1,6-enynes with alkyl bromides, furnishing chiral five-membered heterocycles with high regioselectivity and stereochemical fidelity. Mechanistic studies reveal that the arylative cyclization of 1,6-enynes is initiated by the oxidative addition of Ni(0) to aryl halides and the alkylative cyclization is triggered by the oxidative addition of Ni(0) to allylic acetates. The utility of this strategy is further demonstrated in the enantioselective synthesis of the antiepileptic drug Brivaracetam.

Nickel-Catalyzed Reductive anti-Arylative Cyclization of Alkynyl Enones with Aryl Halides.

A nickel-catalyzed reductive anti-arylative cyclization of alkynyl enones with aryl halides has been developed. The reaction avoids the use of stoichiometric organometallic reagents and has a broad reaction scope and high functional group tolerance. This method offers an efficient way to access a variety of synthetically useful carbocycles that are widely found in many natural products and biologically active molecules.

Optimization of a compact on-site stormwater runoff treatment system: Process performance and reactor design.

Stormwater runoff has become a major anthropogenic urban pollution source that threatens water quality. In this study, coagulation-sedimentation, and ammonium ion exchange and regeneration (AIR) modules were coupled as a CAIR system to efficiently treat stormwater runoff. In the coagulation module, 99.3%, 91.7%, and 97.0% of turbidity, total phosphorus, and chemical oxygen demand could be removed at an optimized poly-aluminum ferric chloride dosage of 30 mg/L, and the continuous experiment confirmed that the full load mode was more suitable for its rapid start-up. In the AIR module, dynamic ammonium removal indicated that the breakthrough time decreased with the rising initial concentration and superficial velocity. The Modified Dose Response (MDR) model described the ammonium exchange behavior better than the Thomas and the Bohart-Adams models. Then, a design flow of the ion exchange reactor was constructed by correlating constants in the MDR model with engineering parameters, and the ion exchange reactor was designed for continuous operation of the CAIR system. The average concentrations of chemical oxygen demand, total phosphorus, ammonium nitrogen, and total nitrogen in the effluent of the CAIR system were 7.22 ± 2.26, 0.17 ± 0.05, 1.49 ± 0.01, and 1.62 ± 0.02 mg/L, respectively. The almost unchanged exchange capacity and physicochemical properties after the multicycle operation confirmed the durability of zeolite for ion exchange. Techno-economic analysis suggested that the CAIR system is practically promising for stormwater management with efficient pollutants removal, small footprint, and acceptable operating cost.

Performance and microbial community of MBBRs under three maintenance strategies for intermittent stormwater treatment.

Maintaining microbial activities is a critical problem for biological treatment processes of stormwater runoff because of its intermittent nature. In this study, the suitability of the moving bed biofilm reactor (MBBR) was assessed for stormwater treatment by long-term dry - rainy alternation operation. Three strategies to maintain microbial activities during the dry period, including keeping idle (MBBRI), introducing river water throughout the period (MBBRC), and ahead of a rainy day (MBBRM), were investigated. COD and NH4+-N removal efficiencies declined linearly from 94.2 % and 94.7 % to 51.7 % and 64.6 %, respectively, after the 61-day operation with microbial activity and biomass decreased. Introducing river water adversely affected the process performance as MBBRC presented the highest declining rates of COD and NH4+-N removal efficiencies. Most genera in MBBRs decayed and their microbial communities developed towards individualization, especially in MBBRM because of its highest environmental variability. Keeping idle slightly alleviated the performance decline and formed a more stable microbial community structure. However, significantly deteriorating performance in all MBBRs after the long-term operation indicated that MBBRs were unsuitable for treating stormwater independently of intermittent nature.

Spatial Distributions and Intrinsic Influence Analysis of Cr, Ni, Cu, Zn, As, Cd and Pb in Sediments from the Wuliangsuhai Wetland, China.

The spatial distributions of Cr, Ni, Cu, Zn, As, Cd and Pb (potentially toxic elements, PTEs) in sediments and intrinsic influence factors from the Wuliangsuhai wetland of the Hetao Irrigation District, China were studied in this work. The results showed that excluding Zn, the total contents of other PTEs were higher than the background values, of which As (39.26 mg·kg-1) and Cd (0.44 mg·kg-1) were six-fold and seven-fold higher, respectively. Especially, the high levels of Cd (70.17%), Pb (66.53%), and Zn (57.20%) in the non-residual fraction showed high bioavailability and mobility. It indicated that PTEs can enter the food chain more easily and produce much toxicity. Based on Igeo, ICF, and MRI, the contamination of As was the most serious in the middle areas (MDP) of the wetland, and its risk was up to moderately strong. Cd and Pb posed moderate and considerate risk, respectively. Furthermore, 29.50% and 55.54% risk contribution ratio of As and Cd, respectively, showed that they were the dominant contaminants. In addition, the positive correlation between sand, OM, and total contents and chemical fractions of PTEs by using PCM, RDA, and DHCA indicated that physicochemical properties could significantly influence the spatial distributions of PTEs. The work was useful for assessing the level of pollution in the study area and acquiring information for future and possible monitoring and remediation activities.