Search

The ability to selectively functionalize ubiquitous C-H bonds streamlines the construction of complex molecular architectures from easily available precursors. Here we report enzyme catalysts derived from a cytochrome P450 that use a nitrene transfer mechanism for the enantioselective amination of primary, secondary and tertiary C(sp3)-H bonds. These fully genetically encoded enzymes are produced and function in bacteria, where they can be optimized by directed evolution for a broad spectrum of enantioselective C(sp3)-H amination reactions. These catalysts can aminate a variety of benzylic, allylic and aliphatic C-H bonds in excellent enantioselectivity with access to either antipode of product. Enantioselective amination of primary C(sp3)-H bonds in substrates that bear geminal dimethyl substituents furnished chiral amines that feature a quaternary stereocentre. Moreover, these enzymes enabled the enantioconvergent transformation of racemic substrates that possess a tertiary C(sp3)-H bond to afford products that bear a tetrasubstituted stereocentre, a process that has eluded small-molecule catalysts. Further engineering allowed for the enantioselective construction of methyl-ethyl stereocentres, which is notoriously challenging in asymmetric catalysis.

High‐valent iron‐oxo species are one of the common intermediates in both biological and biomimetic catalytic oxidation reactions. Recently, hydrogen‐bonding (H‐bonding) has been proved to be critical in determining the selectivity and reactivity. However, few examples have been established for mechanistic insights into the H‐bonding effect. Moreover, intramolecular H‐bonding effect on both C‐H activation and oxygen atom transfer (OAT) reactions in synthetic porphyrin model system has not been investigated yet. In this study, a series of heme‐containing iron(IV)‐oxo porphyrin species with or without intramolecular H‐bonding are synthesized and characterized. Kinetic studies revealed that intramolecular H‐bonding can significantly enhance the reactivity of iron(IV)‐oxo species in OAT, C‐H activation, and electron‐transfer reactions. This unprecedented unified H‐bonding effect is elucidated by theoretical calculations, which showed that intramolecular H‐bonding interactions lower the energy of the anti‐bonding orbital of iron(IV)‐oxo porphyrin species, resulting in the enhanced reactivities in oxidation reactions irrespective of the reaction type. To the best of the knowledge, this is the first extensive investigation on the intramolecular H‐bonding effect in heme system. The results show that H‐bonding interactions have a unified effect with iron(IV)‐oxo porphyrin species in all three investigated reactions. [ABSTRACT FROM AUTHOR]

The development of boron reagents is crucial for synthetic chemistry. Herein, we present a scalable and practical synthesis of diborodichloromethane (DBDCM) through the reaction of trichloromethyllithium with bis(pinacolato)diboron (B2pin2). The resulting DBDCM reagent serves as a basic synthetic unit for the construction of various structurally diverse gem‐diborylalkanes through controllable C−Cl functionalizations. Moreover, we have developed consecutive tetra‐functionalizations of DBDCM for the construction of diverse tertiary and quaternary carbon containing molecules. The use of isotopically enriched 13C‐chloroform and 10B2pin2 enables the synthesis of isotopically enriched 13C‐DBDCM and 10B‐DBDCM reagents, which are beneficial for the convenient synthesis of carbon‐13 and boron‐10 molecules. [ABSTRACT FROM AUTHOR]

Carbon-hydrogen (C-H) and carbon-carbon (C-C) bonds are the main constituents of organic matter. Recent advances in C-H functionalization technology have vastly expanded our toolbox for organic synthesis.sup.1. By contrast, C-C activation methods that enable editing of the molecular skeleton remain limited.sup.2-7. Several methods have been proposed for catalytic C-C activation, particularly with ketone substrates, that are typically promoted by using either ring-strain release as a thermodynamic driving force.sup.4,6 or directing groups.sup.5,7 to control the reaction outcome. Although effective, these strategies require substrates that contain highly strained ketones or a preinstalled directing group, or are limited to more specialist substrate classes.sup.5. Here we report a general C-C activation mode driven by aromatization of a pre-aromatic intermediate formed in situ. This reaction is suitable for various ketone substrates, is catalysed by an iridium/phosphine combination and is promoted by a hydrazine reagent and 1,3-dienes. Specifically, the acyl group is removed from the ketone and transformed to a pyrazole, and the resulting alkyl fragment undergoes various transformations. These include the deacetylation of methyl ketones, carbenoid-free formal homologation of aliphatic linear ketones and deconstructive pyrazole synthesis from cyclic ketones. Given that ketones are prevalent in feedstock chemicals, natural products and pharmaceuticals, these transformations could offer strategic bond disconnections in the synthesis of complex bioactive molecules. Aromatization-driven C-C bond activation through iridium/phosphine catalysis enables deacylative transformations in various ketone substrates., Author(s): Yan Xu [sup.1] , Xiaotian Qi [sup.2] , Pengfei Zheng [sup.1] [sup.3] , Carlo C. Berti [sup.1] , Peng Liu [sup.2] , Guangbin Dong [sup.1] Author Affiliations: (1) Department [...]

Evaluating waterlogging vulnerability and analyzing its characteristics and future trends can provide scientific support for urban disaster prevention and reduction. For this study, taking Fuzhou as an example, an urban waterlogging vulnerability assessment system was constructed from the three dimensions of exposure, sensitivity, and adaptive capacity. The entropy method was used to evaluate urban waterlogging vulnerability in Fuzhou during 2014–2020. The use of CA–Markov to predict waterlogging vulnerability in 2023, 2026, and 2029 in Fuzhou is an important innovation reported in this paper. Study results showed that: (1) Vulnerability to waterlogging in Fuzhou follows a gradually decreasing "center-southeast" distribution pattern, with Level 5 areas mainly located in Cangshan District, Gulou District, and Taijiang District. (2) Changes in waterlogging vulnerability in Fuzhou from 2014 to 2020 can be divided into five change modes, with changing areas, mainly of the late-change type, accounting for 14.13% of the total area. (3) Prediction accuracy verification shows that the CA–Markov model is suitable for predicting waterlogging vulnerability in Fuzhou with high accuracy and a kappa coefficient of 0.9079. (4) From 2020 to 2029, the vulnerability level of the eastern coastal region of Fuzhou is expected to generally increase, and the vulnerability degree will continue to deteriorate. The proportion of Level 5 vulnerable areas will increase by 4.5%, and the growth rate will increase faster and faster with the passage of time. [ABSTRACT FROM AUTHOR]

Methods that can simultaneously install multiple different functional groups to heteroarenes via C−H functionalizations are valuable for complex molecule synthesis, which, however, remain challenging to realize. Here we report the development of vicinal di‐carbo‐functionalization of indoles in a site‐ and regioselective manner, enabled by the palladium/norbornene (Pd/NBE) cooperative catalysis. The reaction is initiated by the Pd(II)‐mediated C3‐metalation and specifically promoted by the C1‐substituted NBEs. The mild, scalable, and robust reaction conditions allow for a good substrate scope and excellent functional group tolerance. The resulting C2‐arylated C3‐alkenylated indoles can be converted to diverse synthetically useful scaffolds. The combined experimental and computational mechanistic study reveals the unique role of the C1‐substituted NBE in accelerating the turnover‐limiting oxidative addition step. [ABSTRACT FROM AUTHOR]

Due to the increase in frequency and severity, assessing and predicting urban waterlogging risk is critical. The risk assessment framework is based on three factors: hazard, exposure, and vulnerability. The assessment indicators, previously based solely on static indicators, account for the effects of varying temporal and spatial distributions of people and vehicles on the assessment results. Specifically, two dynamic indicators—the population density and the Traffic Performance Index (TPI)—are added to the mix to dynamically assess the risk of waterlogging in the central urban area of Suqian City of Jiangsu Province, China's central urban area, over various periods. The findings indicate that four–six times more individuals are affected during peak hours than during other periods, and no important roads are within the scope of waterlogging during other periods, while nearly ten important roads will be affected during peak hours. Additionally, the characteristics of the temporal and spatial distribution of waterlogging risk can be more accurately represented by a combination of static and dynamic indicators. The highest risk areas are significantly more prominent during the weekday peak period than during other times; the morning peak is mainly affected by traffic performance indicators, the evening peak is mainly affected by population density, and the main factors affecting the other periods are the same as the other main factors affecting the peak period. The highest risk areas are mainly located in the eastern part of the central urban area of Suqian City, with the lowest risk in the north and south. [ABSTRACT FROM AUTHOR]

To mitigate the incidence of waterlogging to livelihoods and property security, a combination of management measures has been necessary to achieve optimal benefits, reducing the risk caused by waterlogging to the development of the urban ecology. Thus, this study aims to analyze the sensitivity and sensitivity range of management measures under different rainfall conditions, focusing on establishing a foundation for their combined implementation. Based on different rainfall scenarios, the modified Morris method is employed to assess the sensitivity of key factors and subsequently determine their respective sensitivity ranges. The findings reveal that the sensitivity rankings for total overflow volume and maximum pipe flow are as follows: pipe volume per hectare (PV-H), proportion of impervious area (P-Imperv), and slope. Additionally, analyzing the variation pattern of sensitivity with factors highlight the high sensitivity ranges. As for total overflow volume, a very high sensitivity is observed when the P-Imperv ranges from 36.8% to 82.7% (Niujiaolong community) and from 82.7% to 94.5% (Zhuyuan community). Similarly, when PV-H is less than 148 (Niujiaolong community) and 89.6 (Zhuyuan community), the sensitivity of PV-H to total overflow volume is very high. Nevertheless, the slope had a lower influence on the sensitivity in the study areas. These findings provide a complete analysis of the management measures sensitivity, which can be valuable for creating optimal urban waterlogging management systems. [ABSTRACT FROM AUTHOR]

Green technology adoption is indispensable for sustainable growth. Therefore, this study examines the determinants of green innovation in BRICS countries considering the Triple Bottom Line Theory (social, environmental, and economic). A cross-sectional autoregressive distributed lag (CS-ARDL) model is applied for empirical analysis from 1990 to 2019. The findings show that social, economic, and environmental factors significantly derive green innovation in the long run. However, their marginal contribution is substantially varied. A 1% increase in economic factors increases green innovation by 0.290%, while environmental concerns induce innovation by 0.438% in the long run. In contrast, social factors possess a relatively lower influence on green innovation, with a coefficient magnitude of 0.175%. Lastly, globalization stimulates green innovation by 0.310%. Similar results are observed in the short run; however, the magnitude of variables is significantly lower than long-run. These results are also validated using alternative estimators and recommend TBL factors as core drivers of green innovation in BRICS countries. [ABSTRACT FROM AUTHOR]

Precisely introducing two similar functional groups into bulk chemical alkenes represents a formidable route to complex molecules. Especially, the selective activation of two electrophiles is in crucial demand, yet challenging for cross‐electrophile‐coupling. Herein, we demonstrate a redox‐mediated electrolysis, in which aryl nitriles are both aryl radical precursors and redox‐mediators, enables an intermolecular alkene 1,2‐diarylation with a remarkable regioselectivity, thereby avoiding the involvement of transition‐metal catalysts. This transformation utilizes cyanoarene radical anions for activating various aryl halides (including iodides, bromides, and even chlorides) and affords 1,2‐diarylation adducts in up to 83 % yield and >20 : 1 regioselectivity with more than 80 examples, providing a feasible approach to complex bibenzyl derivatives. [ABSTRACT FROM AUTHOR]

This paper explores whether the sponge city construction implemented in China can restore the hydrological condition of the river basins through runoff depth. The annual runoff depth was calculated based on the volume capture ratio of annual rainfall (VCRAR) and compared with undeveloped and before sponge city construction. The results conclude as follows: the current rainwater source control standard benefits the hydrology recovery in China. But the difference between before sponge city construction and undeveloped is large in 12.9% of the regions. The adjustment recommendations of the VCRAR proposed in this paper are favourable to restoring the river basin hydrology. [ABSTRACT FROM AUTHOR]

This report describes the unprecedented electrooxidation of a solvent (e.g. DMF)‐ligated B2cat2 complex, whereby a solvent‐stabilized boryl radical is formed via quasi‐homolytic cleavage of the B−B bond in a DMF‐ligated B2cat2 radical cation. Cyclic voltammetry and density functional theory provide evidence to support this novel B−B bond activation strategy. Furthermore, a strategy for the electrochemical gem‐diborylation of gem‐bromides via paired electrolysis is developed for the first time, affording a range of versatile gem‐diborylalkanes, which are widely used in synthetic society. Notably, this reaction approach is scalable, transition‐metal‐free, and requires no external activator. [ABSTRACT FROM AUTHOR]

Building up new and efficient methods for the controlled conversion of carboxylic acids to aldehydes is important. Herein, we report a rapid, modular and scalable method for the conversion of carboxylic acids to aldehydes using pinacolborane at ambient temperature, in which a triflylpyridinium reagent is used. The conversion of carboxylic acid to intermediate acylpyridinium by triflylpyridinium is new. A binary pyridine‐coordinated boronium complex is generated after reduction. The unprecedented reduction of the acylpyridinium by HBpin opens up a practically direct synthesis of aldehydes from carboxylic acids. Theoretical studies indicate that the reduction of acylpyridinium requires a lower activation free energy than that of the product aldehyde. The synthetic advantage of this protocol is further highlighted by the scalable synthesis of aldehyde via continuous flow process. Configuration retention for chiral acids are presented in those syntheses. [ABSTRACT FROM AUTHOR]

The development of a mild and general method for C(sp3)−H functionalization of cyclic amines has been an ongoing challenge. In this work, we describe the copper‐catalyzed enantioselective C(sp3)−H alkynylation of unactivated cyclic 2‐iodo‐benzamide under photo‐irradiation by intramolecular 1,5‐hydrogen atom transfer (HAT). The employment of a new bisoxazoline diphenylamine ligand, in conjunction with 1,1′‐bi‐2‐naphthol, which significantly improved the reduction potential of the copper complex, was the key to success of this chemistry. Mechanistic and computational studies supported that the new copper complex served the dual role as a photoredox and coupling catalyst, the reaction went through a radical process, and the intramolecular 1,5‐HAT process was involved in the rate‐limiting step. Apart from the broad substrate scope including unprecedented benzocyclic amines, this method also showed excellent diastereoselectivity in 2‐monosubstituted cyclic amines via substrate control. [ABSTRACT FROM AUTHOR]

Stereoselective cyclopropanation reaction of alkenes is usually achieved by metal complexes via singlet‐metal‐carbene intermediates. However, previous transition‐metal‐catalyzed cyclopropanation of alkenes with acylsilanes afforded low diastereoselectivity. Herein, we report the first visible‐light‐induced transition‐metal‐free cyclopropanation reaction of terminal alkenes with trifluoroacetylsilanes and difluoroacetylsilanes. Both aromatic and aliphatic alkenes as well as electron‐deficient alkenes are suitable substrates for the highly cis‐selective [2+1] cyclization reaction. A combination of experimental and computational studies identified triplet carbenes as being key intermediates in this transformation. The gram scale reaction and late‐stage functionalization demonstrated the synthetic potential of this strategy. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Mechanistic studies of the palladium catalyst activation with halide additives are of great importance to palladium catalysis. In this work, XAFS spectroscopy and cyclic voltammetry were utilized to study real structures of Pd(OAc)2 in solution with different inorganic halogen additives. XAFS results demonstrate that Pd maintained +2 in the presence of excessive LiCl, LiBr, ZnCl2, ZnBr2, and NaI. Fitting results of EXAFS spectra revealed that the Pd's first shell is replaced by halogen partially or completely depending on the halogen species. DFT calculations were conducted to identify the most reliable solvated structures. The combined experimental and computational studies elucidate the critical role of inorganic halide additives in Pd chemistry. [ABSTRACT FROM AUTHOR]

A new bifunctional ligand bearing chiral N‐heterocyclic carbene (NHC) and prolinol moieties is presented. Utilizing the designed ligand, an in situ formed Cu/Zn hetero‐bimetallic complex unlocks the asymmetric allylic alkylation reactions of allyl phosphates with zinc keto‐homoenolates, leading to the formation of various γ‐vinyl ketones with good regio‐ and enantio‐selectivity. DF sT calculation supports that the chelation of allyl phosphates with catalyst promotes the SN2' addition and the ligand‐substrate steric interactions account for the stereoselective outcome. [ABSTRACT FROM AUTHOR]

A method was developed for ketone synthesis via a photoredox‐assisted reductive acyl cross‐coupling (PARAC) using a nickel/photoredox dual‐catalyzed cross‐electrophile coupling of two different carboxylic acid esters. A variety of aryl, 1°, 2°, 3°‐alkyl 2‐pyridyl esters can act as acyl electrophiles while N‐(acyloxy)phthalimides (NHPI esters) act as 1°, 2°, 3°‐radical precursors. Our PARAC strategy provides an alternative and reliable way to synthesize various sterically congested 3°‐3°, 3°‐2°, and aryl‐3° ketones under mild and highly unified conditions, which have been otherwise difficult to access. The combined experimental and computational studies identified a Ni0/NiI/NiIII pathway for ketone formation. [ABSTRACT FROM AUTHOR]