Photocatalyst-Free Visible Light-Induced C(sp2)-H Arylation of Quinoxalin-2(1H)-ones and coumarins.

Herein, we describe a visible light-induced C(sp2)-H arylation method for quinoxalin-2(1H)-ones and coumarins using iodonium ylides without the need for external photocatalysts. The protocol demonstrates a broad substrate scope, enabling the arylation of diverse heterocycles through a simple and mild procedure. Furthermore, the photochemical reaction showcases its applicability in the efficient synthesis of biologically active molecules. Computational investigations at the CASPT2//CASSCF/PCM level of theory revealed that the excited state of quinoxalin-2(1H)-one facilitates electron transfer from its π bond to the antibonding orbital of the C-I bond in the iodonium ylide, ultimately leading to the formation of an aryl radical, which subsequently participates in the C-H arylation process. In addition, our calculations reveal that via single- electron transfer (SET) process, the C-I bond cleavage in iodonium ylide and new C-C bond formation between resultant aryl radical and cationic quinoxaline species take place in a concerned manner. This enables the arylation reaction to efficiently proceed along an energy-efficient route.

Visible-Light-Promoted C3-Sulfenylindoles with Arylsulfonyl Chlorides via Electron Donor-Acceptor Complex.

In this study, we present an efficient approach for the synthesis of 3-sulfenyl indoles through an electron donor-acceptor (EDA) complex-promoted photoreaction. This sulfenylation reaction leverages sulfonyl chlorides as the sulfur source and employs PPh3 as the reductant without the need for any transition-metal catalyst or photocatalyst. At the same time, the relaxation process of the excited EDA complex was theoretically investigated at the method and multiconfiguration second-order perturbation//complete active space self-consistent field/PCM level of theory, which involves the π bond of indoles injecting an electron to the antibonding orbital of the S-Cl bond in arylsulfonyl chlorides.

Heterogeneous Photocatalytic Ring Expansion of Cyclic Ketones for the Construction of Medium-Sized Lactams.

Construction of medium-sized ring compounds remains challenging in synthetic chemistry. Herein, we describe the synthesis of medium-sized lactams via a photoinduced ring expansion of benzo-fused cyclic ketones using graphitic carbon nitride (g-C3N4) as a photocatalyst. The ring expansion protocol provided an efficient access to 8-10-membered lactams in good yields and displayed good tolerance to a range of functional groups. The mechanism studies revealed that the photochemical reaction proceeds via an intermediary of a nitrogen radical, which is generated through an oxidative hydrogen atom transfer (HAT) process.

Rhodium-Catalyzed C(sp2)-O Cross Couplings of Diazo Quinones with Phenols to Construct Diaryl Ethers.

The diaryl ether represents a prevalent structural motif found in numerous biologically active molecules. Herein, we describe a dirhodium-catalyzed C(sp2)-O cross coupling reaction between diazo quinones and phenols for the construction of diaryl ethers in moderate to high yields. The reaction proceeds under mild and neutral conditions and is tolerant of various functional groups. The synthetic method has been successfully applied to the concise synthesis of a Navl.7 inhibitor.

Fabrication of ROS-responsive nanoparticles by modifying the interior pore-wall of mesoporous silica for smart delivery of azoxystrobin.

The suboptimal efficiency in pesticide utilization may elevate residues, posing safety risks to human food and non-target organisms. To address this challenge, delivery systems, such as pathogen infection stimuli-responsive carriers, can be employed to augment the efficiency of fungicide utilization. The bursting of reactive oxygen species (ROS) is a common defense response of host plants to pathogenic infections. In this study, ROS-responsive mesoporous silica nanoparticles (MSN) modified with phenyl sulfide (PHS) as azoxystrobin (AZOX) carrier (MSN-PHS-AZOX) were fabricated. Results demonstrated that MSN-PHS-AZOX exhibited fungicide release kinetics dependent on ROS. In vitro inhibition experiments confirmed the fungicidal effect of MSN-PHS-AZOX on Botrytis cinerea, relying on external ROS. In vivo leaf experiments showcased the superior persistence of MSN-PHS-AZOX in compared to AZOX SC. Furthermore, MSN-PHS-AZOX exhibits favorable biosafety and lower toxicity to aquatic zebrafish compared to AZOX SC, with no adverse impact on cucumber leaf growth. These findings suggest the potential application of this ROS-responsive nano fungicide in managing plant disease in agricultural fields.

Heterogeneous Photocatalytic C-H Functionalization of Indoles with Diazo Compounds Enabled by Carbon Nitride.

Herein, we reported the heterogeneous photocatalytic C-H alkylation of indoles with diazo compounds using graphitic carbon nitride (g-C3N4) as the photocatalyst. The reaction was carried out under a simple operation and mild conditions. In addition, the catalyst was found to be stable and reusable after five reaction cycles. The photochemical reaction proceeds via an intermediary of a carbon radical, which is generated from diazo compounds through a visible-light-promoted proton-coupled electron transfer (PCET) process.

Hypodense regions in the peripapillary region increased the risk of macular retinoschisis detected by optical coherence tomography.

Purpose: The purpose of the present study was to investigate the clinical features of peripapillary regions in patients with myopic macular retinoschisis (MRS) and its association with the development of retinoschisis (RS). Methods: In this cross-sectional study, high-myopic patients with or without MRS were recruited, and the hypodense regions were analyzed in the peripapillary regions. The vitreoretinal adhesions around both macular and paravascular arcades were compared between groups. The risk factors for the development of MRS were analyzed by logistic regression. Results: Of 88 myopic eyes, MRS was detected in 45 eyes (51%). The eyes with MRS showed a higher rate of peripapillary and paravascular retinoschisis (P < 0.001 and P = 0.006). Hypodense regions were detected in 25 eyes (20.35%). Higher rates of horizontal and vertical macular MRS were detected in the hypodense group (P = 0.012 and P = 0.002). Lower refractive error, longer axial length, and higher rates of outer retinoschisis both in horizontal and vertical macular regions were observed in the hypodense group (P = 0.012, P = 0.006, P = 0.038, and P = 0.034). Higher rates of inner and outer retinoschisis, vitreoschisis, and microfolds along superior vascular arcade were detected in the hypodense group (P = 0.005, P = 0.001, P = 0.014, and P = 0.014). Higher rates of internal limiting membrane (ILM) detachment, inner and outer RS were detected along the inferior vascular arcade in the hypodense group (P = 0.008, P = 0.001, and P = 0.028). Hypodense regions, the axial length and PICC (peripapillary intrachoroidal cavitation) were significantly correlated with the severity of MRS (Odds ratio = 0.207, P = 0.010; Odds ratio = 1.399, P = 0.016; Odds ratio = 0.142, P = 0.010). Conclusions: The hypodense regions were likely to affect outer retinoschisis both in macular and paravascular regions. It was a risk factor for the development of MRS.

Metal-Free Generation of γ-Cyanoalkyl Radicals by N-Heterocyclic Carbene Catalysis: Assembly of 6-Cyanoalkyl Phenanthridines.

A number of γ-cyanoalkyl radicals were generated by sustainable N-heterocyclic carbene catalysis in tin-, transition-meal-, and light-free conditions, followed by insertion into biaryl isonitriles, thus leading to the rapid assembly of a variety of diversely functionalized 6-cyanoalkyl phenanthridines. A preliminary mechanism study revealed that a single-electron transfer radical process was possibly involved.

Asymmetric dearomative cyclopropanation of naphthalenes to construct polycyclic compounds.

Catalytic asymmetric dearomatization (CADA) reactions is an important synthetic method for constructing enantioenriched complex cyclic systems from simple aromatic feedstocks. However, the CADA reactions of nonactivated arenes, such as naphthalenes and benzenes, have been far less explored than those of electronically activated arenes, such as phenols, naphthols and indoles. Herein, we disclose an asymmetric dearomative cyclopropanation of naphthalenes for the rapid construction of polycyclic compounds. With chiral dirhodium carboxylate as a catalyst, the dearomative cyclopropanation proceeded smoothly under mild conditions and afforded benzonorcaradiene-containing tetracycles in good yield and high enantioselectivity (up to 99% ee). Three stereogenic centers, including two all-carbon quaternary centers, were created in the dearomatization reaction. Moreover, a variety of functional groups are well-tolerated in the reaction. The products could be readily converted into other complex polycycles while maintaining the high ee value.

Divergent Construction of Heterocycles by SOMOphilic Isocyanide Insertion under N-Heterocyclic Carbene Catalysis.

A variety of phenanthridines are rapidly constructed by an N-heterocyclic carbene (NHC)-catalyzed SOMOphilic isocyanide insertion-initiated homolytic aromatic substitution-type radical cyclization in the absence of any light, transition metals, and external oxidants. The aldehyde-free, scalable, and operationally simple protocol tolerates diverse functionalized biaryl isonitriles and activated α-halides. Moreover, it can be further applied to the divergent construction of other N-heterocycles. Preliminary mechanistic studies disclose that an NHC-derived radical cation intermediate is possibly involved.

Assessing Macro Disease Index of Wheat Stripe Rust Based on Segformer with Complex Background in the Field.

Wheat stripe rust (WSR) is a foliar disease that causes destructive damage in the wheat production context. Accurately estimating the severity of WSR in the autumn growing stage can help to objectively monitor the disease incidence level of WSR and predict the nationwide disease incidence in the following year, which have great significance for controlling its nationwide spread and ensuring the safety of grain production. In this study, to address the low accuracy and the efficiency of disease index estimation by traditional methods, WSR-diseased areas are segmented based on Segformer, and the macro disease index (MDI) is automatically calculated for the measurement of canopy-scale disease incidence. The results obtained with different semantic segmentation algorithms, loss functions, and data sets are compared for the segmentation effect, in order to address the severe class imbalance in disease region segmentation. We find that: (1) The results of the various models differed significantly, with Segformer being the best algorithm for WSR segmentation (rust class F1 score = 72.60%), based on the original data set; (2) the imbalanced nature of the data has a significant impact on the identification of the minority class (i.e., the rust class), for which solutions based on loss functions and re-weighting of the minority class are ineffective; (3) data augmentation of the minority class or under-sampling of the original data set to increase the proportion of the rust class greatly improved the F1-score of the model (rust class F1 score = 86.6%), revealing that re-sampling is a simple and effective approach to alleviating the class imbalance problem. Finally, the MDI was used to evaluate the models based on the different data sets, where the model based on the augmented data set presented the best performance (R2 = 0.992, RMSE = 0.008). In conclusion, the deep-learning-based semantic segmentation method, and the corresponding optimization measures, applied in this study allow us to achieve pixel-level accurate segmentation of WSR regions on wheat leaves, thus enabling accurate assessment of the degree of WSR disease under complex backgrounds in the field, consequently providing technical support for field surveys and calculation of the disease level.

Construction of N-Polyheterocycles by N-Heterocyclic Carbene Catalysis via a Regioselective Intramolecular Radical Addition/Cyclization Cascade.

N-Polyheterocycles are rapidly accessed by N-heterocyclic carbene (NHC) catalysis through regioselective sequential radical addition/cyclization in the absence of any metals or oxidants. The transformation occurs under mild conditions and enjoys a wide substrate scope with excellent functional group compatibility. Furthermore, a gram-scale synthesis is also conducted. Preliminary mechanistic studies reveal the potential involvement of an NHC radical cation intermediate.

Halogen-Bonding-Promoted C-H Malonylation of Indoles under Visible-Light Irradiation.

Herein, we report a halogen-bonding-based electron donor-acceptor (EDA) complex-promoted photoreaction for the synthesis of C2-malonylated indoles. The protocol provides access to a broad range of functionalized indoles in good yields through the coupling reaction of indoles with diethyl bromomalonate under visible-light irradiation without the need for any transition-metal catalyst or photocatalyst.

Visible-Light Carbon Nitride-Catalyzed Aerobic Cyclization of Thiobenzanilides under Ambient Air Conditions.

A metal-free heterogeneous photocatalysis has been developed for the synthesis of benzothiazoles via intramolecular C-H functionalization/C-S bond formation of thiobenzanilides by inexpensive graphitic carbon nitride (g-C3N4) under visible-light irradiation. This reaction provides access to a broad range of 2-substituted benzothiazoles in high yields under an air atmosphere at room temperature without addition of a strong base or organic oxidizing reagents. In addition, the catalyst was found to be stable and reusable after five reaction cycles.

Chemoselective Rearrangement Reactions of Sulfur Ylide Derived from Diazoquinones and Allyl/Propargyl Sulfides.

Here, we describe three types of rearrangement reactions of sulfur ylide derived from diazoquinones and allyl/propargyl sulfides. With Rh2(esp)2 as the catalyst, diazoquinones react with allyl/propargyl sulfides to form a sulfur ylide, which undergoes a chemoselective tautomerization/[2,3]-sigmatropic rearrangement reaction, a Doyle-Kirmse rearrangement/Cope rearrangement cascade reaction, or a Doyle-Kirmse rearrangement/elimination reaction, depending on the substituent of the sulfides. The protocol provides alkenyl and allenyl sulfides and multisubstituted phenols with moderate and high yields.

Transition-Metal-Free C(sp2 )-C(sp2 ) Cross-Coupling of Diazo Quinones with Catechol Boronic Esters.

A transition-metal-free C(sp2 )-C(sp2 ) bond formation reaction by the cross-coupling of diazo quinones with catechol boronic esters was developed. With this protocol, a variety of biaryls and alkenyl phenols were obtained in good to high yields under mild conditions. The reaction tolerates various functionalities and is applicable to the derivatization of pharmaceuticals and natural products. The synthetic utility of the method was demonstrated by the short synthesis of multi-substituted triphenylenes and three bioactive natural products, honokiol, moracin M, and stemofuran A. Mechanistic studies and density functional theory (DFT) calculations revealed that the reaction involves attack of the boronic ester by a singlet quinone carbene followed by a 1,2-rearrangement through a stepwise mechanism.

Iron-Catalyzed Highly Enantioselective cis-Dihydroxylation of Trisubstituted Alkenes with Aqueous H2 O2.

Reliable methods for enantioselective cis-dihydroxylation of trisubstituted alkenes are scarce. The iron(II) complex cis-α-[FeII (2-Me2 -BQPN)(OTf)2 ], which bears a tetradentate N4 ligand (Me2 -BQPN=(R,R)-N,N'-dimethyl-N,N'-bis(2-methylquinolin-8-yl)-1,2-diphenylethane-1,2-diamine), was prepared and characterized. With this complex as the catalyst, a broad range of trisubstituted electron-deficient alkenes were efficiently oxidized to chiral cis-diols in yields of up to 98 % and up to 99.9 % ee when using hydrogen peroxide (H2 O2 ) as oxidant under mild conditions. Experimental studies (including 18 O-labeling, ESI-MS, NMR, EPR, and UV/Vis analyses) and DFT calculations were performed to gain mechanistic insight, which suggested possible involvement of a chiral cis-FeV (O)2 reaction intermediate as an active oxidant. This cis-[FeII (chiral N4 ligand)]2+ /H2 O2 method could be a viable green alternative/complement to the existing OsO4 -based methods for asymmetric alkene dihydroxylation reactions.

Iron- and cobalt-catalyzed C(sp3)-H bond functionalization reactions and their application in organic synthesis.

Direct C-H bond functionalization catalyzed by non-precious transition metals is an attractive strategy in synthetic chemistry. Compared with the precious metals rhodium, palladium, ruthenium, and iridium commonly used in this field, catalysis based on non-precious metals, especially the earth-abundant ones, is appealing due to the increasing demand for environmentally benign and sustainable chemical processes. Herein, developments in iron- and cobalt-catalyzed C(sp3)-H bond functionalization reactions are described, with an emphasis on their applications in organic synthesis, i.e., the synthesis of natural products and pharmaceuticals and/or their modification.

Stable group 8 metal porphyrin mono- and bis(dialkylcarbene) complexes: synthesis, characterization, and catalytic activity.

Alkyl-substituted carbene (CHR or CR2, R = alkyl) complexes have been extensively studied for alkylcarbene (CHR) ligands coordinated with high-valent early transition metal ions (a.k.a. Schrock carbenes or alkylidenes), yet dialkylcarbene (CR2) complexes remain less developed with bis(dialkylcarbene) species being little (if at all) explored. Herein, several group 8 metal porphyrin dialkylcarbene complexes, including Fe- and Ru-mono(dialkylcarbene) complexes [M(Por)(Ad)] (1a,b, M = Fe, Por = porphyrinato dianion, Ad = 2-adamantylidene; 2a,b, M = Ru) and Os-bis(dialkylcarbene) complexes [Os(Por)(Ad)2] (3a-c), are synthesized and crystallographically characterized. Detailed investigations into their electronic structures reveal that these complexes are formally low-valent M(ii)-carbene in nature. These complexes display remarkable thermal stability and chemical inertness, which are rationalized by a synergistic effect of strong metal-carbene covalency, hyperconjugation, and a rigid diamondoid carbene skeleton. Various spectroscopic techniques and DFT calculations suggest that the dialkylcarbene Ad ligand is unique compared to other common carbene ligands as it acts as both a potent σ-donor and π-acceptor; its unique electronic and structural features, together with the steric effect of the porphyrin macrocycle, make its Fe porphyrin complex 1a an active and robust catalyst for intermolecular diarylcarbene transfer reactions including cyclopropanation (up to 90% yield) and X-H (X = S, N, O, C) insertion (up to 99% yield) reactions.

Iron porphyrin catalysed light driven C-H bond amination and alkene aziridination with organic azides.

Visible light driven nitrene transfer and insertion reactions of organic azides are an attractive strategy for the design of C-N bond formation reactions under mild reaction conditions, the challenge being lack of selectivity as a free nitrene reactive intermediate is usually involved. Herein is described an iron(iii) porphyrin catalysed sp3 C-H amination and alkene aziridination with selectivity by using organic azides as the nitrogen source under blue LED light (469 nm) irradiation. The photochemical reactions display chemo- and regio-selectivity and are effective for the late-stage functionalization of natural and bioactive compounds with complexity. Mechanistic studies revealed that iron porphyrin plays a dual role as a photosensitizer and as a catalyst giving rise to a reactive iron-nitrene intermediate for subsequent C-N bond formation.