Ruthenium(II)-Catalyzed [4 + 2] Electro-Oxidative Annulation of C6-Arylpurines/Purine Nucleosides.

A sustainable pathway for the synthesis of tetracyclic purinium salts via ruthenium-catalyzed electro-oxidative annulation of C6-arylpurine nucleosides with alkynes without a stoichiometric metal oxidant has been developed. The protocol described herein exhibits high regioselectivity, broad scope, and wide functional group tolerance, allowing efficient coupling of various biologically important molecules including acyclic, ribosyl, arabinosyl, and deoxyribosyl purine nucleoside derivatives. A novel purinoisoquinolinium-coordinated ruthenium(0) sandwich intermediate has been isolated, crystallographically characterized, and electrochemically analyzed, offering direct mechanistic insight.

Rhodium(III)-Catalyzed Synthesis of Diverse Fluorescent Polycyclic Purinium Salts from 6-Arylpurine Nucleosides and Alkynes.

Described herein is an efficient strategy for assembling a new library of functionalized polycyclic purinium salts with a wide range of anions through RhIII-catalyzed C-H activation/annulation of 6-arylpurine nucleosides with alkynes under mild reaction conditions. The resulting products displayed tunable photoluminescence covering most of the visible spectrum. Mechanistic insights delineated the rhodium catalyst's mode of action. A purinoisoquinolinium-coordinated rhodium(I) sandwich complex was well characterized and identified as the key intermediate.

Facilitating Rh-Catalyzed C-H Alkylation of (Hetero)arenes and 6-Arylpurine Nucleosides (Nucleotides) with Electrochemistry.

An electrochemical approach to promote the ortho-C-H alkylation of (hetero)arenes via rhodium catalysis under mild conditions is described. This approach features mild conditions with high levels of regio- and monoselectivity that tolerate a variety of aromatic and heteroaromatic groups and offers a widely applicable method for late-stage diversification of complex molecular architectures including tryptophan, estrone, diazepam, nucleosides, and nucleotides. Alkyl boronic acids and esters and alkyl trifluoroborates are demonstrated as suitable coupling partners. The isolation of key rhodium intermediates and mechanistic studies provided strong support for a rhodium(III/IV or V) regime.

Electrooxidative Iridium-Catalyzed Regioselective Annulation of Benzoic Acids with Internal Alkynes.

Electrochemically driven, Cp*Ir(III)-catalyzed regioselective annulative couplings of benzoic acids with alkynes have been established herein. The combination of iridium catalyst and electricity not only circumvents the need for stoichiometric amount of chemical oxidant, but also ensures broad reaction compatibility with a wide array of sterically and electronically diverse substrates. This electrochemical approach represents a sustainable strategy as an ideal alternative and supplement to the oxidative annulations methodology to be engaged in the synthesis of isocoumarin derivatives.

Divergent rhodium-catalyzed electrochemical vinylic C-H annulation of acrylamides with alkynes.

α-Pyridones and α-pyrones are ubiquitous structural motifs found in natural products and biologically active small molecules. Here, we report an Rh-catalyzed electrochemical vinylic C-H annulation of acrylamides with alkynes, affording cyclic products in good to excellent yield. Divergent syntheses of α-pyridones and cyclic imidates are accomplished by employing N-phenyl acrylamides and N-tosyl acrylamides as substrates, respectively. Additionally, excellent regioselectivities are achieved when using unsymmetrical alkynes. This electrochemical process is environmentally benign compared to traditional transition metal-catalyzed C-H annulations because it avoids the use of stoichiometric metal oxidants. DFT calculations elucidated the reaction mechanism and origins of substituent-controlled chemoselectivity. The sequential C-H activation and alkyne insertion under rhodium catalysis leads to the seven-membered ring vinyl-rhodium intermediate. This intermediate undergoes either the classic neutral concerted reductive elimination to produce α-pyridones, or the ionic stepwise pathway to produce cyclic imidates.

[Effects of fertilizer application on yield and fertilizer utilization of Coffea arabica in southwest dry-hot region of China under different shading levels]. / 不同遮荫条件下施肥量对西南干热区小粒咖啡产量和肥料利用的影响.

The fertilizer and shading management of Coffea arabica in dry-hot area is extensive, resulting in lower yield and fertilizer utilization efficiency. A field experiment was carried out to find the coupling mode of shading and fertilizer for fertilizer-saving and high yield of C. arabica in dry-hot region. Four shading levels (100% NR, 75% NR, 60% NR, 45% NR, NR was natural radiation) and four fertilizer levels (No fertilization and 666.67, 1000, 1333.33 kg·hm-2) were set to examine the effects of different radiations and fertilizer treatments on canopy structure, yield, ferti-lizer use efficiency, soil nutrient content and microbial biomass carbon of C. arabica. The results showed that canopy structure, yield, fertilizer use efficiency, soil nutrient content and microbial biomass carbon were significantly affected by shading and fertilizer treatments. Soil nutrient content and microbial biomass carbon decreased with the increases of shading levels. Soil nutrient content increased with the increases of fertilizer application, while microbial biomass carbon increased first and then decreased, with a peak at the rate of 1000 kg·hm-2(200.30 mg·kg-1). Shading and fertilizer had significant effects on the canopy structure including leaf area index and openness. There were significant negative correlations of leaf area index with openness, gap fraction, total fixed-point factor and total radiation under canopy. Results of response surface analysis and spatial analysis showed that the combination of shading level and fertilizer application were 80% NR and 666.67 kg·hm-2, 79% NR and 1286.81 kg·hm-2, 79% NR and 967.74 kg·hm-2, 82% NR and 1075.27 kg·hm-2, respectively, when partial fertilizer productivity, yield, fertilizer agronomic efficiency and yield increase of fertilizer reached the maximum. The ranges of shading and fertilizer were 68%-77% NR and 946.24-1178.79 kg·hm-2 when the yield, agronomic efficiency and yield increasing rate by fertilizer reached 80% of the maximum value. In this experiment, the optimum combination of shading level and fertilizer application was 75% NR and 1000 kg·hm-2.

Site-Selective C-H Functionalization via Synergistic Use of Electrochemistry and Transition Metal Catalysis.

Electrochemical synthesis of organic compounds has emerged as an attractive and environmentally benign alternative to conventional approaches for oxidation and reduction of organic compounds that utilizes electric current instead of chemical oxidants and reductants. As such, many useful transformations have been developed, including the Kolbe reaction, the Simons fluorination process, the Monsanto adiponitrile process, and the Shono oxidation, to name a few. Electrochemical C-H functionalization represents one of the most promising reaction types among many electrochemical transformations, since this process avoids prefunctionalization of substrates and provides novel retrosynthetic disconnections. However, site-selective anodic oxidation of C-H bonds is still a fundamental challenge due to the high oxidation potentials of C-H bonds compared to organic solvents and common functional groups. To overcome this issue, indirect electrolysis via the action of a mediator (a redox catalyst) is regularly employed, by which the selectivity can be controlled following reaction of said mediator with the substrate. Since the redox potentials of transition metal complexes can be easily tuned by modification of the ligand, the synergistic use of electrochemistry and transition metal catalysis to achieve site-selective C-H functionalization is an attractive strategy. In this Account, we summarize and contextualize our recent efforts toward transition metal-catalyzed electrochemical C-H functionalization proximal to a suitable directing group. We have developed C-H oxygenation, acylation, alkylation, and halogenation reactions in which a Pd(II) species is oxidized to a Pd(III) or Pd(IV) intermediate by anodic oxidation, followed by reductive elimination to form the corresponding C-O, C-C, and C-X bonds. Importantly, improved monofunctionalization selectivity is achieved in the Pd-catalyzed C(sp3)-H oxygenation compared to conventional approaches using PhI(OAc)2 as the chemical oxidant. Physical separators are sometimes used to prevent the electrochemical deposition of Pd black on the cathode resulting from reduction of high valent Pd species. We skirted this issue through the development a Cu-catalyzed electrochemical C(sp2)-H amination using n-Bu4NI as a redox cocatalyst in an undivided cell. In addition, we developed Ir-catalyzed electrochemical vinylic C-H functionalization of acrylic acids with alkynes in an undivided cell, affording various substituted α-pyrones in good to excellent yield. More importantly, chemical oxidants, including Ag2CO3, Cu(OAc)2, and PhI(OAc)2, resulted in much lower yields in the absence of electrical current under otherwise identical conditions. As elaborated below, progress in the area of electrochemical transition metal-catalyzed synthesis provides an effective platform for environmentally friendly and sustainable selective chemical transformations.

Copper-Catalyzed Electrochemical Selective Bromination of 8-Aminoquinoline Amide Using NH4Br as the Brominating Reagent.

A simple and mild protocol for copper-catalyzed bromination of quinoline at the C5 site of quinoline by anodic oxidation was developed, affording the desired remote C-H activation products with isolated yields of up to about 90%. The reaction proceeds with low-cost NH4Br and shows mild and green conditions (electricity as a green oxidant; NH3 and H2 as byproducts). At the same time, a gram-scale bromination reaction was also successfully fulfilled, showing its potential applicable value in organic synthesis. Moreover, the CV chart further demonstrated the proposed catalytic cycle.

Electrochemistry-Enabled Ir-Catalyzed Vinylic C-H Functionalization.

Synergistic use of electrochemistry and organometallic catalysis has emerged as a powerful tool for site-selective C-H functionalization, yet this type of transformation has thus far mainly been limited to arene C-H functionalization. Herein, we report the development of electrochemical vinylic C-H functionalization of acrylic acids with alkynes. In this reaction an iridium catalyst enables C-H/O-H functionalization for alkyne annulation, affording α-pyrones with good to excellent yields in an undivided cell. Preliminary mechanistic studies show that anodic oxidation is crucial for releasing the product and regeneration of an Ir(III) intermediate from a diene-Ir(I) complex, which is a coordinatively saturated, 18-electron complex. Importantly, common chemical oxidants such as Ag(I) or Cu(II) did not give significant amounts of the desired product in the absence of electrical current under otherwise identical conditions.

Palladium-Catalyzed Electrochemical C-H Bromination Using NH4Br as the Brominating Reagent.

The palladium-catalyzed electrochemical C-H bromination of benzamide derivatives under divided cells is developed, in which NH4Br serves as a brominating reagent and electrolyte. The protocol avoids the use of chemical oxidants and provides an alternative method for the synthesis of aryl bromides.

Nickel-catalyzed Enantioselective Hydroarylation and Hydroalkenylation of Styrenes.

We have developed a Ni-catalyzed enantioselective hydroarylation of styrenes with arylboronic acids using MeOH as the hydrogen source, providing an efficient method to access 1,1-diarylalkanes, which are essential structural units in many biologically active compounds. In addition, Ni-catalyzed enantioselective hydrovinylation of styrenes with vinylboronic acids is also realized with good yields and enantioselectivities. The synthetic utility was demonstrated by the efficient synthesis of ( R)-(-)-ibuprofen.

[Effects of deficit irrigation on water-radiation use and yield of Coffea arabica under different shade cultivation modes in dry-hot region]. / ä¸åŒè«è”½æ ½åŸ¹ä¸‹äºç¼ºçŒæº‰å¯¹å¹²çƒ­åŒºå°ç²’å’–å•¡æ°´å ‰åˆ©ç”¨å’Œäº§é‡çš„å½±å“.

The yield and quality of Coffea arabica cannot be guaranteed due to irrational irrigation and light management in dry-hot region. To investigate the best coupling mode of irrigation and shade cultivation of C. arabica in dry-hot region, a field experiment was carried out with different irrigation levels and shade cultivation modes. Three levels of irrigation, i.e., full irrigation, light deficit irrigation and severe deficit irrigation, and four modes of shade cultivation, i.e., no shade cultivation (C. arabica monoculture), light shade cultivation (intercropping of four-line C. arabica and a line banana), moderate shade cultivation (intercropping of three-line C. arabica and a line banana) and severe shade cultivation (intercropping of two-line C. arabica and a line banana) were designed to examine the effects of deficit irrigation on growth, photosynthetic characteristics of lea-ves, water-radiation use and yield of C. arabica under the shade of banana trees. The results showed that net photosynthesis rate (Pn), transpiration rate (Tr), stomatal conductance (gs), leaf water use efficiency (LWUE), leaf radiation use efficiency (LRUE) increased with the increases of irrigation amount, while the intercellular CO2 concentration (Ci) decreased with the increases of irrigation amount. Compared with full irrigation, light deficit irrigation decreased dry bean yield by 9.4%, severe deficit irrigation decreased dry bean yield and water use efficiency (WUE) by 36.7% and 16.9%, respectively. Pn, Tr, gs, LWUE first increased and then decreased with the increases of shading degree, with moderate shade cultivation having the maximum increment. Compared with no shade cultivation, light shade cultivation increased dry bean yield and WUE by 13.0% and 12.9%, respectively; moderate shade cultivation increased dry bean yield and WUE by 23.1% and 23.4%, respectively. The dry bean yield, WUE, volume and fresh mass of 100-bean of C. arabica increased in different degrees with the increases of irrigation amount and shading degree, with the largest enhancement of dry bean yield and WUE occurring in full irrigation under moderate shade cultivation. Soil water content in the same soil depth decreased with the increases of shading degree. Soil water content in the same place increased first and then decreased with the increases of soil la-yer depth in 0-50 cm soil layer. Results of regression analysis showed that LRUE had a significantly negative exponential relation or Logistic-curve variation with photosynthetically active radiation. Therefore, the suitable combination of irrigation treatment and banana shade cultivation mode for C. arabica was full irrigation and moderate shade cultivation, considering the comprehensive benefit of superior quality and high production and high efficiency water-radiation use.

Copper-Catalyzed Electrochemical C-H Amination of Arenes with Secondary Amines.

Electrochemical oxidation represents an environmentally friendly solution to conventional methods that require caustic stoichiometric chemical oxidants. However, C-H functionalizations merging transition-metal catalysis and electrochemical techniques are, to date, largely confined to the use of precious metals and divided cells. Herein, we report the first examples of copper-catalyzed electrochemical C-H aminations of arenes at room temperature using undivided electrochemical cells, thereby providing a practical solution for the construction of arylamines. The use of n-Bu4NI as a redox mediator is crucial for this transformation. On the basis of mechanistic studies including kinetic profiles, isotope effects, cyclic voltammetric analyses, and radical inhibition experiments, the reaction appears to proceed via a single-electron-transfer (SET) process, and a high valent Cu(III) species is likely involved. These findings provide a new avenue for transition-metal-catalyzed electrochemical C-H functionalization reactions using redox mediators.

[Coupling mode of irrigation and shading for good quality and proper yield of Coffea arabica in dry-hot region]. / 干热区小粒咖啡提质增产的灌水和遮荫耦合模式.

In a field experiment with three levels of irrigation, i.e., CI, DI75 and DI50(100%, 75% and 50% full irrigation) and four levels of shade, i.e., T100, T70, T55 and T40(100%, 70%, 55% and 40% natural radiation), the effects of irrigation and shading levels on growth, yield and quality of Coffea arabica were examined. The comprehensive benefit evaluation model was established under different irrigation and shading levels. The results showed that DI75 treatment increased the contents of fat and chlorogenic acid in dry bean by 6.0% and 10.2%, DI50 treatment significantly increased the content of caffeine of dry bean, but reduced water use efficiency. Compared with T100, T70 treatment increased the yield of dry bean and water use efficiency by 27.2% and 26.8%, respectively, and increased total sugar and chlorogenic acid content in dry bean by 6.3% and 5.5%. T55 and T40 treatments significantly reduced the yield of dry bean, water use efficiency, and the contents of caffeine and chlorogenic acid of dry bean. Compared with CIT100, DI75T70 treatment increased dry bean yield and water use efficiency by 28.0% and 44.5%, and increased the contents of total sugar, protein, fat and chlorogenic acid of dry bean by 12.2%, 14.7%, 6.6% and 10.0%, respectively, but reduced the concentration of caffeine by 8.3%. The comprehensive benefit of yield and quality of DI75T70 treatment (75% full irrigation, 70% natural radiation) was the best, which could implement good quality and proper yield of C. arabica.

Palladium-Catalyzed C(sp2)-H Acetoxylation via Electrochemical Oxidation.

Palladium-catalyzed arene C(sp2)-H acetoxylation has emerged as a powerful tool to construct a carbon-oxygen (C-O) bond. However, the requirement of stoichiometric chemical oxidants for this transformation possesses a significant disadvantage. To solve this fundamental problem, we now report an anodic oxidation strategy to achieve arene C(sp2)-H acetoxylation.

Palladium-Catalyzed C(sp3)-H Oxygenation via Electrochemical Oxidation.

Palladium-catalyzed C-H activation/C-O bond-forming reactions have emerged as attractive tools for organic synthesis. Typically, these reactions require strong chemical oxidants, which convert organopalladium(II) intermediates into the PdIII or PdIV oxidation state to promote otherwise challenging C-O reductive elimination. However, previously reported oxidants possess significant disadvantages, including poor atom economy, high cost, and the formation of undesired byproducts. To overcome these issues, we report an electrochemical strategy that takes advantage of anodic oxidation of PdII to induce selective C-O reductive elimination with a variety of oxyanion coupling partners.

[Coupling effects of periodic rewatering after drought stress and nitrogen fertilizer on growth and water and nitrogen productivity of Coffea arabica]. / 干旱胁迫-复水与氮肥耦合对小粒咖啡生长和水氮生产力的影响.

The effects of periodic rewatering after drought stress and nitrogen fertilizer on growth, yield, photosynthetic characteristics of leaves and water and nitrogen productivity of Coffea arabica (Katim P7963) were studied under different nitrogen application levels in 2.5 consecutive years. Irrigation (periodic rewatering after drought stress) and nitrogen were designed as two factors, with four modes of irrigation, namely, full irrigation (IF-F: 100%ET0+100%ET0, ET0 was reference crop evapotranspiration), rewatering after light drought stress (IL-F: 80%ET0+100%ET0), rewatering after moderate drought stress (IM-F: 60%ET0+100%ET0) and rewatering after severe drought stress (IS-F: 40%ET0+100%ET0), and three levels of nitrogen, namely, high nitrogen (NH: 750 kg N·hm-2 each time), middle nitrogen (NM: 500 kg N·hm-2 each time), low nitrogen (NL: 250 kg N·hm-2 each time), and nitrogen was equally applied for 4 times. The results showed that irrigation and nitrogen had significant effect on plant height, stem diameter, yield and water and nitrogen productivity of C. arabica, and plant height and stem diameter showed S-curve with the day ordinal number, and leaf photosynthesis decreased significantly under drought stress but most photosynthesis index recovered somewhat after rewatering. Compared with IF-F, IL-F increased dry bean yield by 6.9%, while IM-F and IS-F decreased dry bean yield by 15.2% and 38.5%, respectively; IL-F and IM-F increased water use efficiency by 18.8% and 6.0%, respectively, while IS-F decreased water use efficiency by 12.1%; IL-F increased nitrogen partial productivity by 6.1%, while IM-F and IS-F decreased nitrogen partial productivity by 14.0% and 36.0%, respectively. Compared with NH, NM increased dry bean yield and water use efficiency by 20.9% and 19.3%, while NL decreased dry bean yield and water use efficiency by 42.4% and 41.9%, respectively; NM and NL increased nitrogen partial productivity by 81.4% and 72.9%, respectively. Compared with IF-FNH, IL-FNM increased dry bean yield, water use efficiency and nitrogen partial productivity by 37.6%, 52.9% and 106.4%, respectively. Regression analysis showed that the yield of dry bean was the maximum (2362 kg·hm-2) when the irrigation amount was 318 mm and the nitrogen application amount was 583 kg·hm-2; the water use efficiency was the maximum (0.78 kg·m-3) when the irrigationamount was 295 mm and the nitrogen application amount was 584 kg·hm-2, that's to say when yield of dry bean and water use efficiency reach the maximum value at the same time, the combination was the closest to IL-FNM. Therefore, the best combination of water and nitrogen model for C. arabica was IL-FNM.

A rapid and divergent access to chiral azacyclic nucleoside analogues via highly enantioselective 1,3-dipolar cycloaddition of ß-nucleobase substituted acrylates.

A rapid and divergent access to chiral azacyclic nucleoside analogues has been established via highly exo-selective and enantioselective 1,3-dipolar cycloaddition of azomethine ylides with ß-nucleobase substituted acrylates. Using 1 mol% of a chiral copper complex, various chiral azacyclic nucleoside analogues were obtained in high yields, excellent exo-selectivities and enantioselectivities (98 to >99% ee).

[Effects of irrigation amount on morphological characteristics and water use of Jatropha curcas].

Jatropha curcas is the most promising energy tree, and soil moisture is the key factor which affects the seedling quality and water use efficiency of J. curcas. With aims to evaluate the effect of different irrigation amount on growth, morphological characteristics and water use of J. curcas, a pot experiment was conducted with four irrigation amounts, i. e., W1:472.49 mm, W2: 228.79 mm, W3:154.18 mm and W4:106.93 mm, respectively. Compared with W1 treatment, the leaf area and stem cross-section area of base significantly decreased in W2, W3 and W4 treatments, but Huber value significantly increased, which could improve the efficiency of water transfer from root to shoot, thus enhance the capability of resistance to drought stress. Compared with W, treatment, the healthy index of J. curcas seedlings decreased slightly in W2 treatment but significantly decreased in W3 and W4 treatments. Hence, the irrigation amount from 228.79 to 472.49 mm was beneficial to increase the healthy index of J. curcas seedlings. Compared with W1 treatment, irrigation water was saved by 67.4% in W3 treatment, and the total dry mass and evapotranspiration significantly decreased by 17.4% and 68.6%, and the irrigation water use efficiency and total water use efficiency increased by 153.2% and 163.2%, respectively. In the condition of this study, the irrigation amount of 154.18 mm was beneficial to increase water use efficiency.

[Coupling effect of water and nitrogen on spring maize in Wuwei Oasis of Shiyang River Basin, Northwest China].

To explore the optimal supply model of water and nitrogen for spring maize under limited irrigation in arid Northwest China, a field experiment with orthogonal design was conducted in the Wuwei Oasis region margin of Shiyang River Basin to study the effects of irrigation amount at different growth stages and the nitrogen application rate on the group yield and the water and nitrogen utilization of spring maize. With the increase of nitrogen application rate, the grain yield of spring maize increased, and the highest grain yield was obtained when the nitrogen application rate was 300 kg x hm(-2) and the irrigation amount at jointing stage was 136 mm. The grain irrigation water use efficiency (GIWUE) decreased with increasing irrigation amount. When the irrigation amount in whole growth period was 340 mm, the grain yield and GIWUE were improved simultaneously with increasing nitrogen application rate. The GIWUE reached the maximum when the nitrogen application rate was 300 kg x hm(-2) and the irrigation amount at seedling and grain-filling stages was 34 mm, respectively. The effects of nitrogen application and irrigation on the nitrogen accumulation in the whole plant decreased in the order of nitrogen application rate, irrigation at jointing stage, irrigation at seedling stage, irrigation at grain-filling stage, and irrigation at heading stage. The optimal supply model of water and nitrogen for spring maize in Wuwei Oasis was 300 kg x hm(-2) of nitrogen application plus 34, 136, 68 and 102 mm of irrigation at seedling, jointing, heading and grain-filling stages, respectively.