Achieving Nickel-Catalyzed Reductive C(sp2)-B Coupling of Bromoboranes via Reversing the Activation Sequence.

Transition metal-catalyzed reductive cross-couplings to build C-C/Si bonds have been developed, but the reductive cross-coupling to create the C(sp2)-B bond has not been explored. Herein, we describe a nickel-catalyzed reductive cross-coupling between aryl halides and bromoboranes to construct a C(sp2)-B bond. This protocol offers a convenient approach for the synthesis of a wide range of aryl boronate esters, using readily available starting materials. Mechanistic studies indicate that the key to the success of the reaction is the activation of the B-Br bond of bromoboranes with a Lewis base such as 2-MeO-py. The activation ensures that bromoboranes will react with the active nickel(I) catalyst prior to aryl halides, which is different from the sequence of the general nickel-catalyzed reductive C(sp2)-C/Si cross-coupling, where the oxidative addition of an aryl halide proceeds first. Notably, this approach minimizes the production of undesired homocoupling byproduct without the requirement of excessive quantities of either substrate.

Photoinduced halogen-bonding enabled synthesis of oxindoles and isoindolinones from aryl iodides.

We report the use of halogen bonding (XB) for the generation of aryl radicals from aryl halides under blue light irradiation and applied it in radical generation/1,5-hydrogen-atom transfer/radical cyclization cascade reactions for the synthesis of oxindoles and isoindolinones. On the basis of experimental studies, we propose that DBU can serve as a suitable XB acceptor with aryl halides for the formation of a photoactive electron donor and acceptor complex.

N-Heterocyclic Nitreniums Can Be Employed as Photoredox Catalysts for the Single-Electron Reduction of Aryl Halides.

N-Heterocyclic nitrenium (NHN) salts, the analogues of N-heterocyclic carbenes, have attracted considerable interest. However, relatively little is known about their catalytic ability beyond their Lewis acid catalysis. Herein, we describe that NHNs can serve as catalytic electron acceptors for charge transfer complex photoactivations. We showcase that, under blue light irradiation, the NHN salts could catalyze the generation of aryl radicals from aryl halides.

Combining lanthanum-modified bentonite (LMB) and submerged macrophytes alleviates water quality deterioration in the presence of omni-benthivorous fish.

Bioturbation by omni-benthivorous fish often causes sediment resuspension and internal nutrient loading, which boosts phytoplankton growth and may lead to a shift of clear water lakes to a turbid state. Removal of large-sized omni-benthivorous individuals is a lake restoration measure that may revert lakes from a turbid to a clear water state, yet the rapid reproduction of small omni-benthivorous fish in tropical and subtropical shallow lakes may impede such lake recovery. In lake restoration, also a combination of lanthanum-modified bentonite (LMB) and planting submerged macrophytes has been used that may synergistically improve lake water quality. How the combined effect works in the presence of small omni-benthivorous fish has not been studied, which is needed given the high abundances of small omni-benthivorous fish in (sub)tropical lakes. We conducted a two-by-two factorial mesocosm experiment with and without the submerged macrophytes Vallisneria natans and with and without LMB, all in the presence of small crucian carp. At the end of the experiment, turbidity in the V. natans, LMB and combined LMB + V. natans treatments had decreased by 0.8%, 30.3% and 30.9%, respectively, compared with the controls. In addition, the nitrogen (N) and phosphorus (P) release from the sediment in the combined LMB + V. natans treatments had decreased substantially, by 97.4% and 94.3%, respectively, compared with the control. These N and P fluxes were also significantly lower in the combined LMB + V. natans treatments than in the sole LMB treatment (88.1% and 82.3%) or the V. natans treatment (93.2% and 90.3%). Cyanobacteria in the overlying water in the combined LMB + V. natans treatments significantly decreased by 84.1%, 63.5% and 37.0%, respectively, compared with the control and the sole LMB and V. natans treatments. Our results show that LMB and submerged macrophytes complement each other in effectively improving the water quality, even in the presence of small omni-benthivorous fish.

Slope position- mediated soil environmental filtering drives plant community assembly processes in hilly shrublands of Guilin, China.

Background and aims: A major goal of community ecology focuses on trying to understand how environmental filter on plant functional traits drive plant community assembly. However, slopes positions- mediated soil environmental factors on community-weighted mean (CWM) plant traits in shrub community has not been extensively explored to analyze and distinguish assembly processes. Methods: Here, we surveyed woody shrub plant communities from three slope positions (foot, middle, and upper) in a low hilly area of Guilin, China to assess differences in functional trait CWMs and environmental factors across these positions. We also measured the CWMs of four plant functional traits including specific leaf area, leaf dry matter content, leaf chlorophyll content, and leaf thickness and nine abiotic environmental factors, including soil water content, soil organic content, soil pH, soil total nitrogen, soil total phosphorus, soil total potassium, soil available nitrogen, soil available phosphorus, and soil available potassium. We used ANOVA and Tukey HSD multiple comparisons to assess differences in functional trait CWMs and environmental factors across the three slope positions. We used redundancy analysis (RDA) to compare the relationships between CWMs trait and environmental factors along three slope positions, and also quantified slope position-mediated soil environmental filtering on these traits with a three-step trait-based null model approach. Results: The CWMs of three leaf functional traits and all soil environmental factors except soil pH showed significant differences across the three slope positions. Soil total nitrogen, available nitrogen, available potassium, and soil organic matter were positively correlated with the CWM specific leaf area and leaf chlorophyll content along the first RDA axis and soil total potassium, total phosphorous, and soil water content were positively correlated with the CWM leaf dry matter content along the second RDA axis. Environmental filtering was detected for the CWM specific leaf area, leaf dry matter content, and leaf chlorophyll content but not leaf thickness at all three slope positions. Conclusions: Ultimately, we found that soil environmental factors vary along slope positions and can cause variability in plant functional traits in shrub communities. Deciduous shrub species with high specific leaf area, low leaf dry matter content, and moderate leaf chlorophyll content dominated at the middle slope position, whereas evergreen species with low specific leaf area and high leaf dry matter content dominated in slope positions with infertile soils, steeper slopes, and more extreme soil water contents. Altogether, our null model approach allowed us to detect patterns of environmental filtering, which differed between traits and can be applied in the future to understand community assembly changes in Chinese hilly forest ecosystems.

A donor-acceptor complex enables the synthesis of E-olefins from alcohols, amines and carboxylic acids.

Olefins are prevalent substrates and functionalities. The synthesis of olefins from readily available starting materials such as alcohols, amines and carboxylic acids is of great significance to address the sustainability concerns in organic synthesis. Metallaphotoredox-catalyzed defunctionalizations were reported to achieve such transformations under mild conditions. However, all these valuable strategies require a transition metal catalyst, a ligand or an expensive photocatalyst, with the challenges of controlling the region- and stereoselectivities remaining. Herein, we present a fundamentally distinct strategy enabled by electron donor-acceptor (EDA) complexes, for the selective synthesis of olefins from these simple and easily available starting materials. The conversions took place via photoactivation of the EDA complexes of the activated substrates with alkali salts, followed by hydrogen atom elimination from in situ generated alkyl radicals. This method is operationally simple and straightforward and free of photocatalysts and transition-metals, and shows high regio- and stereoselectivities.

Photoinduced α-Alkenylation of Katritzky Salts: Synthesis of ß,γ-Unsaturated Esters.

ß,γ-Unsaturated esters are building blocks in biologically important compounds, pharmaceuticals, and natural products. Because the current synthetic methods often require transition-metal catalysts or lack general variants, we herein describe a simple NaI-involved photoinduced deaminative alkenylation for their synthesis in the absence of photocatalysts and additives. The density functional theory study unveils that the electrostatic interaction of NaI with Katritzky salts is the key to forming the photoactive electron donor-acceptor complex, thus leading to the alkyl radicals for the alkenylation.

Photochemical Decarboxylative C(sp3)-X Coupling Facilitated by Weak Interaction of N-Heterocyclic Carbene.

While N-hydroxyphthalimide (NHPI) ester has emerged as a powerful reagent as an alkyl radical source for a variety of C-C bond formations, the corresponding C(sp3)-N bond formation is still in its infancy. We demonstrate herein transition-metal-free decarboxylative C(sp3)-X bond formation enabled by the photochemical activity of the NHPI ester-NaI-NHC complex, giving primary C(sp3)-(N)phth, secondary C(sp3)-I, or tertiary C(sp3)-(meta C)phth coupling products. The primary C(sp3)-(N)phth coupling offers convenient access to primary amines.

N-Heterocyclic Carbene Catalyzed Synthesis of Dihydroxybenzophenones from ß-Methylenals and Aurones.

N-heterocyclic carbene catalyzed synthesis of 2,2'-dihydroxybenzophenones from ß-methylenals and aurones was developed. The cleavage of the C-O bond by a retro-Michael addition is the key step from the spirocyclic intermediate to final product.

(Dynamic) Kinetic Resolution of Enamines/Imines: Enantioselective N-Heterocyclic Carbene Catalyzed [3+3] Annulation of Bromoenals and Enamines/Imines.

The enantioselective N-heterocyclic carbene catalyzed [3+3] annulation of α-bromoenals by dynamic kinetic resolution (DKR) of enamines and normal resolution of α,α-disubstituted imines were developed. The corresponding substituted dihydropyridones were isolated in good yields with excellent diastereo- and enantioselectivities, and a high selective factor (up to 83) was realized for the resolution of α,α-disubstituted imines.

Enantioselective N-Heterocyclic Carbene-Catalyzed Synthesis of Spirocyclic Oxindole-benzofuroazepinones.

Herein, we report an enantioselective synthesis of azepinones via the N-heterocyclic carbene (NHC) catalyzed [3+4] annulation reaction of isatin-derived enals and aurone-derived azadienes. The corresponding spirocyclic oxindole-benzofuroazepinones were obtained in good yields, with excellent diastereo- and enantioselectivities. The resulted azepinones were evaluated for their in vitro cytotoxic activities against six human tumor cell lines, with two compounds showing significant inhibitory activity comparable with that of cisplatin.

Diastereo- and Enantioselective Synthesis of Spirooxindoles with Contiguous Tetrasubstituted Stereocenters via Catalytic Coupling of Two Tertiary Radicals.

The oxidative N-heterocyclic carbene-catalyzed [3 + 2] annulation of ß,ß-disubstituted enals and dioxindoles was developed, giving the spirocyclic oxindole-γ-lactones bearing two contiguous tetrasubstituted stereocenters in good yields with excellent diastereoselectivities and good enantioselectivities.

Omnidirectional Internal Fixation by Double Approaches for Treating Rüedi-Allgöwer Type III Pilon Fractures.

In the present study, we explored the effectiveness and complications of omnidirectional internal fixation using a double approach for treating Rüedi-Allgöwer type III pilon fractures. A retrospective analysis was performed of 19 cases of Rüedi-Allgöwer type III unilateral closed pilon fracture. With preoperative preparation and correct surgical timing, the reduction was performed using anteromedial and posterolateral approaches, and the fracture fragments were fixed by omnidirectional internal fixation. Imaging evaluation was performed using the Burwell-Charnley scoring system. The Johner-Wruhs scoring system was used to assess the functional status of the patients. A comprehensive evaluation of efficacy was performed using a 5-point Likert score. The complications were also recorded and analyzed. All patients were followed up for an average of 16.2 months. The operative incisions of 15 cases healed by primary intent and with delayed healing in 4. All patients had achieved bony union at an average of 16 weeks postoperatively. No deep infection, broken nail or withdrawn nail, exposed plate, or skin flap necrosis occurred. The Burwell-Charnley imaging evaluation showed that 14 patients had anatomic reduction of the articular surface and 5 had acceptable reduction. Using the Johner-Wruhs scoring system, the results were excellent for 8, good for 7, fair for 2, and poor for 2 patients; the combined rate of excellent and good results was 78.9%. The Likert score of efficacy self-reported by the patients was 3 to 4 points for 12 patients, 2 points for 4 patients, and 0 to 1 point for 3 patients. The Likert score of therapeutic efficacy reported by the physicians was 3 to 4 points for 10 patients, 2 points for 5 patients, and 0 to 1 point for 4 patients. Omnidirectional internal fixation using double approaches was an effective method to treat Rüedi-Allgöwer type III pilon fractures with satisfactory reduction and rigid fixation, good joint function recovery, and few complications.

N-heterocyclic carbene-catalyzed synthesis of spirocyclopentene-oxindoles from bromoenals.

The N-heterocyclic carbene-catalyzed tandem reaction of bromoenals and oxindoles was developed to give the corresponding chiral spirocyclopentene-oxindoles in good yields with good to high diastereo- and enantioselectivities.

N-Heterocyclic carbene-catalyzed oxidative [3 + 2] annulation of dioxindoles and enals: cross coupling of homoenolate and enolate.

The N-heterocyclic carbene-catalyzed oxidative [3 + 2] annulation of dioxindole and enals was developed, giving the corresponding spirocyclic oxindole-γ-lactones in good yields with high to excellent diastereo- and enantioselectivities. The challenging aliphatic enals worked effectively using this strategy. The oxidative cross coupling of homoenolate and enolate via single electron transfer was proposed as the key step for the reaction.

N-Heterocyclic Carbene-Catalyzed [3 + 4] Annulation of Enals and Alkenyl Thiazolones: Enantioselective Synthesis of Thiazole-Fused ε-Lactones.

The bifunctional N-heterocyclic carbene catalyzed [3 + 4] annulation of enals and 5-alkenyl thiazolones was developed, giving the corresponding thiazole-fused ε-lactones in high yields with excellent diastereoselectivties and enantioselectivities. The thiazole-fused ε-lactone could be isomerized to the spirocyclic thiazolone-cyclopentanone without erosion of enantioselectivity.

N-Heterocyclic carbene-catalyzed [3 + 2] annulation of bromoenals with 3-aminooxindoles: highly enantioselective synthesis of spirocyclic oxindolo-γ-lactams.

The chiral N-heterocyclic carbene-catalyzed [3 + 2] annulation of α-bromoenals and 3-aminooxindoles was developed, giving the corresponding spirocyclic oxindolo-γ-lactams in good yields with high diastereoselectivities and enantioselectivities.

N-Heterocyclic carbene-catalyzed [3 + 3] cyclocondensation of bromoenals with hydrazones: highly enantioselective synthesis of dihydropyridazones.

The N-heterocyclic carbene-catalyzed [3 + 3] cyclocondensation of bromoenals and hydrazones is developed to give the corresponding chiral 4,5-dihydropyridazones in good yields with excellent enantioselectivities.

Enantioselective N-heterocyclic carbene-catalyzed synthesis of trifluoromethyldihydropyridinones.

The enantioselective N-heterocyclic carbene-catalyzed [4 + 2] cyclocondensation of α-chloroaldehydes and trifluoromethyl N-Boc azadienes was developed, giving the corresponding 3,4-disubstituted-6-trifluoromethyldihydropyridin-2(1H)-ones in good yields with exclusive cis-selectivities and excellent enantioselectivities.

Enantioselective N-heterocyclic carbene-catalyzed synthesis of indenopyrones.

The chiral N-heterocyclic carbene-catalyzed [4 + 2] cyclization of α-chloroaldehydes and arylidene indanediones was developed, giving the corresponding indenopyrones in good yields with high diastereoselectivities and enantioselectivities.