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Visible light-mediated NHC and photoredox co-catalyzed radical 1,2-sulfonylacylation of allenes via cross-coupling between an allyl radical and an NHC-stabilized acyl radical.

Secondary alcohols bearing both axial and central chirality comprise attractive biological activity, and also exhibit excellent chiral induction in asymmetric reactions. However, only very limited asymmetric catalytic approaches were developed for their catalytic synthesis. We herein describe visible light-mediated cobalt-catalyzed asymmetric reductive Grignard-type addition of axially prochiral biaryl dialdehydes with aryl iodides, leading to the direct construction of axially chiral secondary alcohols bearing aldehyde groups. Preliminary mechanistic studies indicate efficient kinetic recognition of diastereomers might occur to improve the diastereoselectivity, which might open a new avenue for the challenging cascade construction of multiple chiral elements. This protocol features excellent enantio- and diastereoselectivity, green and mild conditions, simple operation, and broad substrate scope, providing a modular platform for the synthesis of secondary axially chiral alcohols.

The modulation of selectivity of highly reactive carbon radical cross-coupling for the construction of C-C bonds represents a challenging task in organic chemistry. N-Heterocyclic carbene (NHC) catalyzed radical transformations have opened a new avenue for acyl radical cross-coupling chemistry. With this method, highly selective cross-coupling of an acyl radical with an alkyl radical for efficient construction of C-C bonds was successfully realized. However, the cross-coupling reaction of acyl radicals with vinyl radicals has been much less investigated. We herein describe NHC and visible light-mediated photoredox co-catalyzed radical 1,4-sulfonylacylation of 1,3-enynes, providing structurally diversified valuable tetrasubstituted allenyl ketones. Mechanistic studies indicated that ketyl radicals are formed from aroyl fluorides

1,3,5-tri-substituted benzene rings emerged with unique properties has widespread applications in materials, boosting the rapid development of their synthesis. Despite the significance, the direct construction of hetero-1,3,5-trisubstituted benzene core was far less-developed. Herein, we realized a DBU-mediated isomerization/6-π electro-cyclization/oxidative aromatization cascade of sulfonyl-substituted allenyl ketones under an air atmosphere. This versatile protocol featured metal-free conditions, easy operation, and broad functional group tolerance provides a new avenue for the construction of hetero-1,3,5-tri-substituted benzene.

The implementation of warm mix asphalt and chemical compaction aids is becoming more widespread. A growing number of contractors are using warm mix asphalt technologies to reduce mixing and compaction temperatures, reduce fuel consumption, improve compatibility, and increase economic and environmental value. In 2009, three pavement overlay projects were constructed in the state of Iowa using both hot mix aphalt and warm mix asphalt mixes to compare their performance. A series of dynamic modulus tests were conducted using field and laboratory mixtures of hot mix asphalt and warm mix asphalt. For each project, twelve specimens, including six hot mix asphalt specimens and six warm mix asphalt specimens, were tested to determine dynamic modulus and phase angles. These results were used as input parameters for designing each pavement in the mechanistic-empirical pavement design guide (MEPDG) and in finite element viscoelastic simulations to predict the performance behavior of warm mix asphalt and hot mix as phalt. A step-by-step framework to convert dynamic modulus results to Prony series to use in finite element simulation models was developed and is detailed for one mixture. This research compared predicted rutting damage by MEPDG design, estimated rutting from finite element simulations, and measured rutting in the field. The results show that MEPDG based on linear elastic theories may overestimate the rutting of pavements while the finite element based on viscoelastic theory accurately predicted the rutting of pavements. Therefore, a series of proposed calibration coefficients from this research can be useful for industrial applications and design engineers to modify and correct MEPDG overlay design thicknesses on top of hot mix asphalt, and jointed plain concrete pavement surfaces with either hot mix asphalt and warm mix asphalt mixtures.

Rh(III)-catalyzed, chelation-assisted oxidative C−H imidation of arenes with N−H imide have been realized using PhI(OAc)2 as an oxidant. This transformation exhibits a broad substrate scope and tolerates various functional groups. The reaction proceeded via in situ generation of an iodine(III) imido. DFT calculations suggest that this oxidative imidaton system proceeds via a Rh(III)-Rh(V)-Rh(III) pathway.

Reported herein is the atroposelective synthesis of biaryl NH isoquinolones by RhIII -catalyzed C-H activation of benzamides and intermolecular [4+2] annulation for a broad scope of 2-substituted 1-alkynylnaphthalenes, as well as sterically hindered, symmetric diarylacetylenes. The axial chirality is constructed based on dynamic kinetic transformation of the alkyne in redox-neutral annulation with benzamides, with alkyne insertion being stereodetermining. The reaction accommodates both benzamides and heteroaryl carboxamides and proceeds in excellent regioselectivity (if applicable) and enantioselectivities (average 91.8 % ee). An enantiomerically and diastereomerically pure rhodacyclic complex was prepared and offers insight into enantiomeric control of the coupling system, wherein the steric interactions between the amide directing group and the alkyne substrate dictate both the regio- and enantioselectivity.

Alkenes are ubiquitous, and radical difunctionalization of alkenes represents one of the most practical approaches to constructing value-added compounds. Dicarbonylation of alkenes provides direct access to value-added 1,4-dicarbonyl compounds. However, selectivity control for unsymmetric 1,2-dicarbonylation is an unclosed challenge. We herein describe NHCs and photocatalysis co-catalyzed three competent radical 1,2-dicarbonylation of alkenes by distinguishing two carbonyl groups, providing structurally diversified 1,4-diketones. Mechanistic studies indicated that NHCs-stabilized ketyl-type radicals originate from aroyl fluorides via oxidative quenching process of excited photocatalysis, and acyl radicals are generated from single-electron-oxidation of α-keto acids. Distinct properties of acyl radical and NHCs-stabilized ketyl radical contributed to selectivity control. Transient acyl radicals are rapidly added to alkenes delivering alkyl radicals, which undergo subsequent radical-radical cross-coupling with ketyl-type radicals, affording 1,2-dicarbonylation products. This transformation features mild reaction conditions, broad substruct scope, and excellent selectivity, providing a general and practical approach for the dicarbonylation of olefins.

Axially chiral aldehydes have received increasing attention in enantioselective catalysis. However, only very few catalytic methods have been developed to construct structurally diverse axially chiral aldehydes. We herein describe an NHC-catalyzed atroposelective esterification of biaryl dialdehydes as a general and practical strategy for the construction of axially chiral aldehydes. Mechanistic studies indicate that coupling proceeds through a novel combination of NHC-catalyzed desymmetrization of the dialdehydes and kinetic resolution. This protocol features excellent enantioselectivity, mild conditions, good functional-group tolerance, and applicability to late-stage functionalization and provides a modular platform for the synthesis of axially chiral aldehydes and their derivatives.

The modulation of selectivity of highly reactive carbon radical cross-coupling for the construction of C-C bonds represents a challenging task in organic chemistry. N-Heterocyclic carbenes (NHCs) catalyzed radical transformations opened a new avenue for acyl radical cross-coupling chemistry. With this method, highly selective cross-coupling of acyl radical with alkyl radical for efficient construction of C-C bonds were succussfully realized. However, the cross-coupling reaction of acyl radical with vinyl radicals represents an uncharted domain. We herein describe NHCs and photocatalysis co-catalyzed radical 1,4-sulfonylacylation of 1,3-enynes, providing structurally diversified valuable tetrasubstituted allenyl ketones. Mechanistic studies indicated that ketyl radicals are formed from aroyl fluorides via oxidative quenching process of excited photocatalysis, allenyl radicals are generated from chemo specific sulfonyl radical addition to the 1,3-enynes, finally, unprecedented key allenyl and ketyl radical cross-coupling provides tetrasubstituted allenyl ketones.

Electro-Fenton-like processes are widely used in removal of antibiotics in sewage owing to their excellent degradation efficiency for organics. However, the degradation mechanisms of antibiotics in electro-Fenton-like systems are still unclear caused by the non-real time detection of current methods. An electrochemical-mass spectrometry (EC-MS) method was developed for in situ analysis and real-time monitoring of electrochemical degradation of antibiotics in this study. In EC-MS, ITO glass was used as an electrochemical reactor and counter electrode, which is positioned in front of the MS inlet. A platinum slice as a working electrode was placed over the ITO glass. When different high voltages were applied on the electrodes, the electrochemical degradation of organics started and a charged spray was generated for MS detection. To enhance the electrochemical reaction efficiency, the voltage difference was optimized. As a proof-of-concept, the degradation of ciprofloxacin (CIP) in an electro-Fenton-like system was monitored, and five intermediates (m/z 330, 304, 348, 346 and 362) different from those obtained in other removal processes were detected and verified. Furthermore, six new characteristic intermediates (m/z 364, 305, 293, 277, 275 and 280) were captured. Meanwhile, the compounds were identified by high-resolution mass spectrometry and tandem mass spectrometry. Extracted ion chromatography (EIC) of several characteristic intermediates was performed for further discussion of the degradation pathway. Based on the data acquired, the degradation mechanism of CIP by an electro-Fenton-like process was proposed for the first time. This work provided a useful tool for mechanism research in electrochemical advanced oxidation processes.

Rh(iii)-catalyzed synthesis of vicinal diamides has been realized via elaboration of an authenticated Rh-C(sp3) species generated via initial intramolecular amidorhodation of olefins. The second amidation was achieved using both electrophilic and nucleophilic amidating reagents. The reactions proceeded under mild conditions with good yield, broad substrate scope, and excellent functional-group tolerance.

Enantiomeric access to pentatomic biaryls is challenging due to their relatively low rotational barrier. Reported herein is the mild and highly enantioselective synthesis of 2,3'-biindolyls via underexplored integration of C-H activation and alkyne cyclization using a unified chiral Rh(III) catalyst. The reaction proceeded via initial C-H activation followed by alkyne cyclization. A chiral rhodacyclic intermediate has been isolated from stoichiometric C-H activation, which offers direct mechanistic insight.

Reported herein is a mild synthesis of 3-allylindoles via Rh(III)-catalyzed allylic C-H activation of olefins and coupling with o-alkynylanilines. The reaction proceeded via initial nucleophilic cyclization of o-alkynylanilines followed by oxidative coupling with allylic C-H bonds via an η3-allyl intermediate.

Pyridines/pyrimidines are common and effective directing groups in C-H activation. However, they are poorly functionalizable heteroarenes. Reported in this work is Mn-catalyzed dehydrocyanative transannulation between three classes of heteroarenes and propargyl carbonates. The pyridyl/pyrimidyl groups in the heteroarenes initially function as directing groups to enable C-H allenylation; they then undergo intramolecular Diels-Alder/retro-Diels-Alder reactions with the allene moiety to afford fused carbo/heterocycles. Three key intermediates at different stages of the reaction were isolated.

Assays utilizing in situ fluorogenic reactions provide a simple and convenient alternative approach for the detection of biological molecules and activities. In this work, a novel ratiometric fluorescent probe based on in situ fluorogenic reaction is explored and developed for alkaline phosphatase (ALP) activity sensing. An intriguing fluorogenic reaction between 2,3-diaminonaphthalene (2,3-DAN) and ascorbic acid (AA) in alkaline aqueous solutions could generate the fluorescent quinoxaline derivative. The resultant quinoxaline emits intense yellow fluorescence, differing from the blue fluorescence of 2,3-DAN. Thus, a ratiometric fluorescent probe based on this fluorogenic reaction is constructed for ALP activity sensing, combining with ALP-triggered hydrolysis of AA2P into AA. Meanwhile, the addition of copper(II) acetate into the reaction system largely improves reaction rate and efficiency. This sensing strategy shows high sensitivity for ALP activity with detection limit of 0.08 U/L, and excellent selectivity towards ALP out of various interferences. This method is extended to human salivary ALP detection. The present method provides a simple and reliable alternative for the detection of ALP activity and has the potential for clinical applications. It also shows a feasible way to construct ratiometric fluorescent methods.

Chemodivergent annulative couplings have been realized between N-methoxy benzamides and 1,3-enynes via Rh-catalyzed C-H activation and 1,4-Rh migration. Under Rh/copper catalyzed aerobic conditions, the nitrogen annulation occurred as the major pathway. The chemoselectivity was switched to the oxygen annulation under proper condition control with stoichiometric amounts of Cu(II) oxidant and NaOAc. Both coupling systems proceeded with a broad scope and functional group tolerance.

Nitrogen-rich heterocyclic compounds have a profound impact on human health. Despite the numerous synthetic methods, diversified, step-economic, and general synthesis of heterocycles remains limited. C-H bond functionalization catalyzed by rhodium(iii) cyclopentadienyls has proven to be a powerful strategy in the synthesis of diversified heterocycles. Herein we describe rhodium(iii)-catalyzed sp2 and sp3 C-H activation-oxidative annulations between aromatic substrates and 1,3-enynes, where alkenyl-to-allyl 1,4-rhodium(iii) migration enabled the generation of electrophilic rhodium(iii) π-allyls via remote C-H functionalization. Subsequent nucleophilic trapping of these species by various sp2-hybridized N-nucleophiles delivered three classes (external salts, inner salts, and neutral azacycles) of five-membered azacycles bearing a tetrasubstituted saturated carbon center, as a result of [4 + 1] annulation with the alkyne being a one-carbon synthon. All the reactions proceeded under relatively mild conditions with broad substrate scope, high efficiency, and excellent regioselectivity. The synthetic applications of this protocol have also been demonstrated, and experimental studies have been performed to support the proposed mechanism.

Cu-catalyzed redox-divergent [3+3] coupling of oxime esters with β-CF3 enones and acrylates is described. This redox-neutral coupling with enones and acrylates affords trifluoromethylated pyridines and pyridones, respectively. Under reductive conditions, difluoromethylated pyridines, difluoromethlated pyridones, and trifluoromethylated dihydropyridones are obtained. The reactions occur under mild conditions with broad substrate scope and regio/redox selectivity.

Redox-neutral synthesis of isoquinolinium salts via C-H activation of presynthesized or in situ formed imines and coupling with α-diazo ketoesters has been realized, where a zinc salt promotes cyclization as well as provides a counteranion. Under three-component conditions, both ketone and aldehydes are viable arene sources. The coupling of imines with diazo malonates under similar conditions afforded isoquinolin-3-ones as the coupling product.

Cp*RhIII /IrIII complexes are known to play important roles in both C-H activation and transfer hydrogenation (TH). However, these two areas evolved separately. They have been integrated in redox- and chemodivergent coupling reactions of N-pyridylanilines with enones. The iridium-catalyzed coupling with enones leads to the efficient synthesis of tetrahydroquinolines through TH from i PrOH. Counterintuitively, i PrOH does not serve as the sole hydride source, and the major reaction pathway involves disproportionation of a dihydroquinoline intermediate, followed by the convergent and iterative reduction of quinolinium species.

A novel nitrogen-centered radical-induced 1,2-carbon migration reaction of allylic alcohols has been developed. This method provides easy access to a variety of α-quaternary-β-amino ketones under mild reaction conditions. The reaction has a wide substrate scope and operational simplicity. Mechanistic studies suggest that 1,2-carbon migration is induced by regioselective nitrogen-centered radical addition to the alkene unit.

The Rh(III)-catalyzed annulative C–H functionalization of arenes with sulfoxonium ylides has been realized. Arenes assisted by diverse nucleophilic directing groups are viable substrates, and the coupling affords structurally diverse fused hetero- and carbocycles under redox-neutral conditions.

Chemodivergent and redox-neutral annulations between N-methoxybenzamides and sulfoxonium ylides have been realized via Rh(III)-catalyzed C–H activation. The sulfoxonium ylide acts as a carbene precursor, and coupling occurs under acid-controlled conditions, where Zn(OTf)2 and PivOH promote chemodivergent cyclizations.

A facile and efficient copper-catalyzed azidative multifunctionalization of alkynes has been developed by using N-fluorobenzenesulfonimide (NFSI) as both nitrogen source and aryl source and trimethylsilyl azide (TMSN3) as azido source. This transformation proceeds under mild conditions, providing a series of α-azido-α-aryl imine in good yields by a single operation starting from a wide range of alkynes. The prepared α-azido-α-aryl imines could be easily converted into 1,5-piperizine-fused 1,2,3-triazoles and azido enamines.

An efficient, atom-economical, and regioselective insertion of indoles into terminal alkynes has been realized via cobalt(III)-catalyzed C–H activation under mild conditions, leading to efficient synthesis of α-gem-vinylindoles. The insertion of the alkynes follows a rare 1,2-selectivity, and silyl alkynes, alkyl alkynes, propargyl alcohols, and protected propargyl amines are all applicable. The mechanism of this hydroarylation system has been studied in detail by a combination of experimental and computational approaches. In the reaction of silyl terminal alkynes, the regioselectivity is dictated by the steric effects of the alkyne substituent, especially in the protonolysis stage. However, for protected propargyl amines, the selectivity results from electronic effects during the insertion step, with protonolysis being insignificant in the determination of selectivity. An internal alkyne also coupled in high efficiency but with low regioselectivity. Comparisons of cobalt, rhodium, and iridium catalysts h...

Sulfoxonium ylides act as an efficient carbene precursor in rhodium(III)-catalyzed C-H acylmethlyation of a variety of arenes assisted by different chelating groups, and both aryl- and alkyl-substituted β-carbonyl sulfoxonium ylides are applicable. The system proceeded under redox-neutral conditions with a broad scope, high efficiency, and functional group tolerance.

The first metal-free, three-component radical aminofluorination of styrene derivatives has been developed, which employs Selectfluor as a fluorine source and azole derivatives as a nitrogen source. This transformation proceeds with high regioselectivity, providing various 1,2-aminofluorination compounds under mild conditions. Mechanistic studies suggest that the aminofluorination process might involve radical fluorination followed by nucleophilic amination.

The first copper-catalyzed imidovinylation of alkynes has been developed, which grants facile access to various (E)-2-imido-2,4-dienals with high stereoselectivity under mild conditions. This transformation also represents the first 1,3-carbon migration of propargylic alcohols and their derivatives.

Reported herein is the Rh(III)-catalyzed annulation of N-unprotected 2-arylindoles with quinone monoacetals for the straightforward synthesis of [4,3,1]-bridged carbocycles with exclusive C(3) selectivity. Mechanistic studies, particularly deuterium-labeling experiments, suggest that the coupling likely proceeds via two-fold C-H activation with two-fold migratory insertion into the enone moieties.

C-H bond activation is mostly limited to ortho selectivity. Activation of both ortho and meta C-H bonds constitutes a particularly important strategy for annulation, but has rarely been studied in enantioselective systems. Reported herein is rhodium(III)-catalyzed asymmetric [3+2] transannulation of arenes with 7-azabenzonorbornadienes. Two distinct classes of arenes have been identified as substrates, and the coupling proceeded with high enantioselectivity and excellent diastereoselectivity through sequential activation of ortho and meta C-H bonds.

Mn(i)-Catalyzed synthesis of seven- or eight-membered carbocycles is disclosed via C-H activation of heteroarenes and coupling with alkyne-functionalized 1,3-cyclopentadiones or 1,3-cyclohexadiones. This n to n + 2 (n = 5, 6) ring expansion reaction proceeded via a C-H alkenylation/carbonyl addition/retro-Aldol cascade. Structurally diverse mid-sized carbocycles were constructed via cleavage of both C-H and C-C bonds in a single operation.

Antibiotics are of concern due to their prevalent detection in aquatic environment. Sulfate radical based advanced oxidation processes show a great capacity to degrade antibiotics, but the mechanisms are still unclear. In this work, the degradation mechanism of fluoroquinolones (FQs), a major group of antibiotics, in UV/Fe

A copper-catalyzed highly regio- and stereospecific selenosulfonation of alkynes with arylsulfonohydrazides and diphenyl diselenide has been developed. This novel three component reaction proceeds under very mild conditions and with a broad scope of substrates, providing a wide range of (E)-β-selenovinyl sulfones in good to excellent yields.

A facile, copper-catalyzed aminoarylation reaction of various aryl/alkyl alkynes was realized by utilizing N-fluoroarylsulfonimides (NFSI) as aminoarylation or amination reagent with hydroxyl as directing group. With this methodology, various α,β-unsaturated carbonyl compounds and indenones were efficiently constructed, and the synthetic application for indole derivatives was also provided. The aminoarylation reactions operate via a regiospecific addition of copper-coordinated nitrogen radical to C–C triple bond/Cvinyl–Caryl bond formation followed by other series of radical processes.

Research implementing new pavement technologies often focuses on material characterization; however, expanding the research to study and validate how new technologies influence pavement design is needed for continual improvement. Numerical analysis approaches use laboratory mixture data to predict field performance. This study compares predicted rutting by MEPDG design, estimated rutting from Finite Element (FE) simulations, and actual rutting performance in the field. Ten years ago, warm mix asphalt research was underway to measure the effect of warm mix asphalt (WMA) additives and lower production temperatures on performance. WMA benefits include reduced mixing/compaction temperatures, reduced fuel consumption, and improved compatibility. In 2009, three asphalt overlay projects were constructed in Iowa using both hot mix asphalt (HMA), and WMA mixes to compare their performance. A series of dynamic modulus tests were conducted to determine dynamic modulus and phase angles of HMA and WMA mixtures. The dynamic modulus results were used to develop FE viscoelastic simulations to predict the rutting of HMA/WMA pavement sections. Iowa’s pavement management system provided field rutting of WMA/HMA sections. Also, pavement sections were evaluated using mixture input parameters in the Mechanistic-Empirical Pavement Design Guide (MEPDG). The results showed MEPDG based on linear elastic theories might overestimate the rutting of asphalt pavements, especially overlays placed on Jointed Plain Concrete Pavement (JPCP). In contrast, the FEM based on viscoelastic theories more accurately predicted the rutting of pavements. Calibration coefficients are proposed by this study, which may be useful for design engineers and industrial applications to correct and modify MEPDG overlay design thicknesses for HMA/WMA mixes placed on HMA and JPCP surfaces.

Novel azacycles were synthesized through rhodium(iii)-catalyzed sp2 and sp3 C–H activation-oxidative annulations between arenes and 1,3-enynes., Nitrogen-rich heterocyclic compounds have a profound impact on human health. Despite the numerous synthetic methods, diversified, step-economic, and general synthesis of heterocycles remains limited. C–H bond functionalization catalyzed by rhodium(iii) cyclopentadienyls has proven to be a powerful strategy in the synthesis of diversified heterocycles. Herein we describe rhodium(iii)-catalyzed sp2 and sp3 C–H activation-oxidative annulations between aromatic substrates and 1,3-enynes, where alkenyl-to-allyl 1,4-rhodium(iii) migration enabled the generation of electrophilic rhodium(iii) π-allyls via remote C–H functionalization. Subsequent nucleophilic trapping of these species by various sp2-hybridized N-nucleophiles delivered three classes (external salts, inner salts, and neutral azacycles) of five-membered azacycles bearing a tetrasubstituted saturated carbon center, as a result of [4 + 1] annulation with the alkyne being a one-carbon synthon. All the reactions proceeded under relatively mild conditions with broad substrate scope, high efficiency, and excellent regioselectivity. The synthetic applications of this protocol have also been demonstrated, and experimental studies have been performed to support the proposed mechanism.

Chiral rhodium(III) cyclopentadienyl catalysts (CpX RhIII ) play significant roles in asymmetric arene C-H activation. Rh/Ir-catalyzed couplings of arenes and strained rings have been well-studied, but they have been limited to racemic systems. Reported in this work is the Cpx RhIII /AgSbF6 -catalyzed enantioselective desymmetrizative C-C coupling of N-pyrimidylindoles and 7-azabenzonorbornadienes with high efficiency and enantioselectivity. The role of AgSbF6 has been established by mechanistic studies. AgSbF6 enhances the catalytic activity by suppressing the C3-H activation of the indoles, activation which would otherwise lead to catalytically inactive species.

Copper-catalyzed cascade aminoalkynylation-oxidation of propargylic alcohols has been realized, sterospecifically providing an array of ( Z)-2-amino conjugated enynals/enynones in good yields under mild conditions. This transformation involves a rare 1,3-alkynyl migration of propargylic alcohols and simultaneously forms C-C, C-N, and C═O bonds. Furthermore, ( Z)-2-amino conjugated enynals were applied to efficiently synthesize 3,5-disubstituted-1 H-pyrrole-2-carbaldehyde and conjugated enynol derivatives.