N-Fluorobenzenesulfonimide: a useful and versatile reagent for the direct fluorination and amination of (hetero)aromatic C–H bonds

This review updates recent advances and developments in the direct fluorination and amination of (hetero)aromatic C–H bonds utilizing N-fluorobenzenesulfonimide, classified according to the type of catalyst.

This review updates recent advances and developments in the direct fluorination and amination of (hetero)aromatic C–H bonds utilizing N-fluorobenzenesulfonimide, classified according to the type of catalyst.     

Novel synthesis of divergent aryl imidazoles from ketones involving copper-catalyzed α-amination and oxidative C–C bond cleavage

A one-pot synthesis, initiated by a copper salt with inorganic (NH₄)₂CO₃ as the nitrogen source, forms divergent aryl imidazole derivatives from ketones via α-amination and oxidative C–C bond cleavage reactions. The approach provides a simple and rapid synthesis of imidazole derivatives and has certain versatility.

A one-pot synthesis, initiated by a copper salt with (NH₄)₂CO₃ as the nitrogen source, forms divergent aryl imidazole derivatives from ketones via C–H activation, α-amination and oxidative C–C bond cleavage and condensation cascade reaction.

The aryl imidazole is a core skeleton for chiral ligands widely used in asymmetric synthesis,¹ as well as many drug molecules and natural products that possess anti-cancer, anti-infection, anti-histamine, anti-ulcer, antihypertensive, and anti-malarial activities (Fig. 1).² Therefore, how to construct an aryl imidazole core is of great significance and has been extensively studied for the development of different synthetic methods.Open in a separate windowFig. 1Bioactive molecules containing aryl imidazole.As early as 1858, imidazoles were first synthesized by Heinrich Debus'' research group,³ and many other synthetic methods have been reported since then. These include the Bredereck synthetic method,⁴ the Leusen reaction,⁵ the Debus-Radziszewski reaction,³ the Claisen rearrangement reaction,⁶ the Phillips method,⁷ the isonitrile synthesis,⁸ and the ketones method (Scheme 1a).⁹ These methods mostly involved the traditional amination process which typically employs indirect synthesis from halogenated hydrocarbons, unsaturated bonds, and/or acyl chlorides. This leads to an increase in the number of reaction steps and limits the diversity of the substrates.Open in a separate windowScheme 1Formation of imidazole derivatives and C–C single-bond cleavage.In the past decade, metal-catalyzed C–H bond activation and amination and the activation of C–C bond cleavage have been favored.^10–13 The activation energy of C–H and C–C bonds cleavage can be reduced by directly metal-catalyzed activation of the C–H and C–C bonds, which makes the reaction easier and simplifies the synthetic process. This resulted in the development of synthetic methods for imidazole skeletons involving metal-catalyzed amination.¹⁴ However, a common problem with these syntheses is that the starting substrates are not readily available so that these solutions are economically unreliable. Recently, a few of the tandem new bond formations after C–C bond cleavage draw our attention. These examples offer the reutilization of the molecule fragments, which can be utilized to synthesize various nitrogen-containing heterocyclic rings with the atomic economy. However, these methods also have some drawbacks and limitations that do not have universal application, such as need of ring tension for C–C bond breaking (Scheme 1b),¹¹ the participation of adjacent groups for C–C bond breaking (Scheme 1c), and C–C bond breaking in α-hydroxyketones and ketones (Scheme 1d and e).¹⁵Following our interest in tandem metal-catalyzed transformation for the heterocyclic synthesis,¹⁶ especially the α-amination catalyzed by transition metal complexes,¹⁷ which is an attractive reaction for the synthesis of amine derivatives and amino-functionalized heterocycles, we explored the metal-catalyzed α-amination reaction of ketones using ammonia released from ammonium carbonate. In transition metal-catalyzed amination, the simple inorganic ammonium salts as the nitrogen source is a change from the conventional nitrogen sources including iodoimines, chloramines T, organic azides, hydroxylamines, NFSI, aromatic nitroso derivatives, and other organic nitrogen-containing compounds. Furthermore, it is surprising that the catalytic α-amination of the ketone results in the tandem reactions for the synthesis of imidazole while producing a small amount of amide. Herein, we report a novel approach of imidazole formation involving α-amination and C–C bond cleavage reaction with an excellent substrate scope.Firstly, using propiophenone as the substrate, we investigated the effect of different reaction conditions on the reaction. As shown in ESI Table 1.^† The use of inexpensive ammonium carbonate as a nitrogen source and copper iodide as a catalyst and readily available starting materials makes this protocol economically visible.Under the optimal reaction conditions, we explored the substrate scope of the reaction (Scheme 2). In this investigation, the corresponding imidazole derivatives (2a–2p) were obtained from the reaction of a series of aromatic ketones. The results show that the substrates with electron-withdrawing groups on the aromatic ring have higher reactivity than the substrates with electron-donating substituents on the aromatic ring with the exception of 2k. The substrates containing electron-withdrawing groups on the aromatic ring afforded moderate to high yield of the imidazole products (2b–2g). In addition, the alkyl chain length of the aryl alkyl ketones also affected the yields of the reaction, and the longer the chain length, the lower the reactivity (2n, 2o). The α-aryl substituted aromatic ketones also can afford the corresponding imidazole product (2p).Open in a separate windowScheme 2Reactivity of the aryl alkyl ketones^[a]. [a] Reactions conditions: CuI (10 mol%), 1 (0.37 mmol), (NH₄)₂CO₃ (7.4 mmol), air, H₂O (0.37 mmol), MeOH (2 mL), and 100 °C for 6 h in a sealed tube.To understand the reaction for novel imidazole synthesis well, we designed a series of experiments to observe the special effects of some conditions on the imidazole synthesis (see ESI^†). The effect of the nitrogen source on the reaction was first investigated. No reaction occurred in the absence of (NH₄)₂CO₃. This result indicates that (NH₄)₂CO₃ is really a nitrogen source for the reaction and it may decompose into ammonia to form a complex with copper and participates in the catalytic cycle. To confirm this point, ammonia-saturated methanol was used as the reaction solvent. The reaction occurred, but the yield of the corresponding product was only 46%. This lower yield may be due to the fact that only a limited amount of ammonia dissolved in methanol. Subsequently, the copper–ammonia complex (Cu[NH₃]₄SO₄) was prepared by the reaction of the copper salt with excess ammonia water and was used in the reaction. The result shows that the product was obtained in 72% yield, which confirmed that the copper–ammonia complex was not only the catalyst of the reaction, but also the nitrogen source. In addition, the effects of air and water on the reaction were also investigated. In the absence of water (anhydrous methanol) or air, no target product was obtained, indicating that water and air play an important role in the cleavage of C–C bond of propiophenone. Further, to confirm the α-C–H activation and α-amination in the imidazole formation, α-perdeuterated propiophenone was used as the substrate using deuterated methanol as a solvent in the presence of dry air and D₂O, the product was obtained in only 11% yield. The results show that C–H activation is a prerequisite for the reaction process.In addition, referring to the C–C bond cleavage reaction,^11,15 during the formation of imidazoles, we speculated that a portion of propiophenone may undergo cleavage of the C–C bond to produce an aldehyde. In order to confirm this, benzaldehyde was added to the reaction system, and only trace amount of original product 2a was found. In contrast, the corresponding aldehyde condensation products was obtained in yields of 66%, respectively. If 4 equivalents of benzaldehyde are added, the formation of 2a can also be completely inhibited. The results indicate that a competitive reaction occurs when an excess of other aldehyde is present, and the root cause is related to more rapidly α-amination than the cleavage of the C–C bond of propiophenone during the reaction. The experimental results make us to use other aldehydes and ketones in the synthesis of divergent aryl imidazoles. As shown in Scheme 3, divergent imidazoles were obtained in excellent yield by adding four equivalents of the aldehyde to the reaction system. Both aliphatic and aromatic aldehydes yield the ideal results, but ketones failed to afford pure corresponding products, the reaction is messy and complicated. It is interesting that when 1,2-diarylethan-1-one replaces propiophenone 1a, the addition of ketones resulted in the formation of corresponding 2H-imidazoles (Scheme 4). Meanwhile, the formation of 4j further indicates that the reaction rate of α-amination is faster than that of C–C bond cleavage. The structures of 2d and 3m, 4a were further confirmed by the X-ray single crystal analysis (the detailed crystal data are provided in the ESI^†).Open in a separate windowScheme 3The formation of divergent imidazoles from propiophenone and aldehydes^[a]. [a] Reactions conditions: CuI (10 mol%), 1a (0.37 mmol), aldehyde (1.48 mmol), (NH₄)₂CO₃ (7.4 mmol), air, MeOH (2 mL), 24 h, 100 °C, in a sealed tube.Open in a separate windowScheme 4The formation of divergent imidazoles from 1,α-biarylethanone.At the same time, ethylamine was used as a nitrogen source and phenylacetone as a substrate to react under the same reaction conditions. The intermediates α-ethylpheny-lacetone, (E)-ethylacetone-1-(ethylimino)-1-phenyl-propan-2-amine and N-ethylbenzamide and their products 1,3-diethyl-4-methyl-ene-5-phenyl-2,3-dihydro-1-himidazole were found by LC-MS (see ESI^†).On the basis of experimental results and the previously proposed mechanisms,¹⁸ a reaction pathway for aryl imidazole synthesis was proposed (Scheme 5). First, Cu(i) is oxidized to Cu(ii) under an oxygen atmosphere. The Cu(ii) species then forms a complex with ammonia (released from ammonium carbonate). Subsequently, the copper–ammonia complex reacts with the substrate to give intermediate A. A is converted into intermediate B after loss of a proton. B then undergoes a disproportionation reaction with NH₂ insertion to afford intermediate C. Intermediate D occurs via cleavage of C–Cu bond. Intermediate E forms via ammonia 1, 2-addition to species D. The intermediate E is then dehydrated to form compound F. Simultaneously, O₂ insertion into the C–Cu bond of intermediate A results in intermediate G. Addition of water then forms intermediate H. An aldehyde is then formed by electron transfer and cleavage of the C–C bond. Finally, the nucleophilic addition reaction of the aldehyde with intermediate F occurs to obtain the imidazole product by further dehydration and loss of a proton.Open in a separate windowScheme 5A proposed reaction pathway for aryl imidazole synthesis.In conclusion, under copper catalysis, the aryl alkyl ketones were reacted with an inorganic salt (NH₄)₂CO₃ in one-pot to form the imidazole derivatives by C–H activated amination and C–C oxidative cleavage. We speculate that in the imidazole synthesis, a portion of aryl alkyl ketones underwent the C–C bond cleavage, and the cleavage fragment is further subjected to a multicomponent cascade reaction with other reaction intermediates to form imidazole derivatives. The approach provides a simple and rapid synthesis for imidazole derivatives and has certain versatility. When the applicability of the reaction was further explored, it was found that the addition of other aldehydes in the reaction of the arylalkyl ketone inhibited the formation of the original product, but produced a new imidazole derivative formed by condensation with the aldehydes. In the aryl alkyl ketone reaction, the addition of other aldehydes and ketones can produce more diverse imidazole derivatives.     

Recrystallized ice-templated electroless plating for fabricating flexible transparent copper meshes

Flexible transparent conductors as a replacement for indium tin oxide (ITO) have been urgently pursued due to the inherent drawbacks of ITO films. Here, we report the fabrication of flexible transparent copper meshes with recrystallized ice-crystal templates. Completely different to conventional approaches, this novel method needs neither the fabrication of mesh patterns via micro/nanofabrication technologies nor the deposition of copper through evaporation or sputtering. The linewidth and mesh size of the prepared copper meshes can be regulated, as the ice recrystallization process is controllable. Therefore, the formed copper meshes have tailorable conductivity and transparency, which are critical for optoelectronic devices. Remarkably, the electrical performance of the copper meshes is maintained even after storing for 60 days in ambient conditions or bending for 1000 cycles. This strategy is modular and can also be employed to prepare other metal meshes, such as silver meshes, offering versatile substitutes for ITO in electronic devices.

Herein, we report the fabrication of flexible copper meshes using recrystallized ice-crystal templates. The linewidth and mean size of the copper meshes can be tuned by adjusting the ice grains.     

Lophiostomin A–D: new 3,4-dihydroisocoumarin derivatives from the endophytic fungus Lophiostoma sp. Sigrf10

Four new 3,4-dihydroisocoumarin congeners, named lophiostomin A–D (1–4), together with two known α-pyridones (5 and 6) were isolated from cultures of the endophytic fungus Lophiostoma sp. Sigrf10 obtained from Siraitia grosvenorii. The structures of the new compounds were determined via combined analysis involving 1D and 2D NMR, high-resolution electrospray ionization mass spectrometry (HRESIMS), and electronic circular dichroism (ECD) spectra, as well as quantum chemical ECD computations for assigning the absolute configurations. All the compounds were evaluated for their antibacterial and antifungal activities. Compounds 1 and 2 displayed moderate inhibitory activities against the spore germination of Magnaporthe oryzae, whereas 5 and 6 were active against the following tested pathogenic bacteria: Bacillus subtilis, Agrobacterium tumefaciens, Ralstonia solanacearum, and Xanthomonas vesicatoria.

Four new 3,4-dihydroisocoumarin congeners, named lophiostomin A–D (1–4), together with two known α-pyridones (5 and 6) were isolated from cultures of the endophytic fungus Lophiostoma sp. Sigrf10 obtained from Siraitia grosvenorii.     

Electromagnetic and microwave absorption properties of iron pentacarbonyl pyrolysis-synthesized carbonyl iron fibers

The present study executed iron pentacarbonyl pyrolysis to synthesize one-dimensional structured carbonyl iron fibers (CIFs) via carrier gas induced flow. The obtained CIFs with a diameter of 100–300 nm and length–diameter ratio of more than 20, are actually composed of a large number of nanocrystalline aggregates. We investigated the dependence of the structure, morphology, and static magnetic and electromagnetic properties of the CIFs on the pyrolysis temperatures. CIFs synthesized at 300 °C (denoted as CIF-300) exhibited optimal microwave absorption properties dependent on the fiber structure and well-matched impedance. An optimal reflection loss of −58.1 dB was observed at 13.8 GHz with a matching thickness of 1.43 mm. Furthermore, CIF-300 presented a broad effective absorption bandwidth (RL ≤ −10 dB) of 5.66 GHz with a thickness of 1.44 mm, indicating that it could be applied in practical applications from 3.74 GHz to 18.0 GHz by tuning its thickness from 1.0 mm to 4.0 mm. This paper not only reveals that the CIFs synthesized at 300 °C have great potential application in microwave absorbing materials (MAMs) with thin thicknesses, wide absorption bandwidths, and strong absorption intensities, but also provides a simple approach to prepare metal fibers.

Carbonyl iron fibers synthesized at 300 °C exhibit a minimum RL of −58.1 dB and an effective absorption bandwidth of 5.66 GHz.     

Enhanced sintering resistance of bimetal/SBA-15 catalysts with promising activity under a low temperature for CO methanation

According to its thermodynamic equilibrium analysis and strong exothermic characteristics, the major challenge of syngas methanation is to develop a high-efficient low-temperature catalyst with superior sintering resistance. In this study, bimetal-based SBA-15 catalysts were prepared via a citric acid-assisted impregnation method and applied in CO methanation. The obtained catalysts were characterized via X-ray diffraction, N₂ adsorption–desorption, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, H₂ temperature-programmed reduction and other techniques. Combining the structural characterization of the fresh and used catalyst, the function of the organic additive and metal promoters was revealed. The catalysts exhibited superior low-temperature activity and excellent sintering resistance owing to the electron migration from the additive metal to Ni, strong interaction between the metal and support and the confinement effect of the support. The catalyst with Mo as a promotor exhibited the best dispersion and the largest surface concentration of nickel, which resulted in its highest catalytic activity among the catalysts. The design and preparation of a highly effective catalyst can provide novel insight into the preparation of other catalysts.

Well-dispersed bimetallic catalysts with confinement effects and strong interaction lead to superior low-temperature activity and excellent thermostability.     

Endoscopic transnasal odontoidectomy to treat basilar invagination with congenital osseous malformations

Purpose

Transoral resection of the odontoid has been accepted as a standard procedure to decompress the cervicomedullary junction during the past several decades. The endoscopic transnasal odontoidectomy is emerging as a feasible surgical alternative to conventional microscopic transoral approach. In this article, we describe several operative nuances and pearls from our experience about this approach, which provided successful decompression.

Methods

From September 2009 to April 2010, three consecutive patients with basilar invagination, of which the etiology was congenital osseous malformations, underwent endoscopic transnasal odontoidectomy. All patients presented with myelopathy. The last two cases also received occipitocervical fixation and bone fusion during the same surgical episode to ensure stability.

Results

All the patients were extubated after recovery from anesthesia and allowed oral food intake the next day. Cerebrospinal fluid rhinorrhea was found in the second case and cured by continuous lumber drainage of cerebrospinal fluid. No infection was noted. The average follow-up time was more than 24 months. Remarkable neurological recovery was observed postoperative in all patients.

Conclusion

The endoscopic transnasal odontoidectomy is a feasible approach for anterior decompression of pathology at the cervicomedullary junction. The advantages over the standard transoral odontoidectomy include elimination of risk of tongue swelling and teeth damaging, improvement of visualization, alleviation of prolonged intubation, reduction of need for enteral tube feeding and less risk of affecting phonation. The minimally invasive access and faster recovery associated with this technique make it a valid alternative for decompression of the ventral side of the cervicomedullary junction.     

经皮肾镜联合输尿管镜气压弹道碎石治疗输尿管石街

目的探讨经皮肾镜取石术（percutaneous nephrolithotripsy,PCNL）联合经尿道输尿管镜气压弹道碎石治疗输尿管石街的可行性。方法 2008年3月～2011年10月对27例经B超、KUB、泌尿系CT三维重建等检查确诊的输尿管石街,在输尿管镜下气压弹道加水冲将石街推至肾盂或输尿管上段,再行PCNL。结果 23例1次取石成功,3例2次取石成功,1例因输尿管下端闭锁无法进镜,仅行经皮肾造瘘置管引流术。19例随访3～12个月,平均6个月,8例积水完全消失,7例轻度积水,4例中度积水,无出血、输尿管梗阻、结石复发。结论 PCNL联合输尿管镜气压弹道治疗输尿管石街,疗效确切、安全。     

Validation of the prognostic value of lymph node ratio in patients with penile squamous cell carcinoma: a population-based study

Purpose

The aim of this study was to validate the prognostic value of lymph node ratio (LNR), the proportion of metastatic among removed lymph nodes, for patients with penile squamous cell carcinoma in a population-based database.

Methods

A total of 210 eligible patients with node-positive disease were identified from the surveillance epidemiology end results database. Cancer-specific survival (CSS) was the clinical outcome of interest. The prognostic ability of LNR was assessed by Cox regression analyses. Logrank test was used to compare CSS between low-risk and high-risk groups stratified by cutoff points of LNR.

Results

The median number of LNs removed was 16, and the median value of LNR was 0.20. First, LNR was a significant prognostic factor of CSS in univariate analysis (HR = 4.08). Second, LNR retained independent predictive ability (HR = 6.74) in the multivariate model including demographic data, disease characteristics and number-based LN variables. Addition of LNR remarkably improved the predictive accuracy and clinical usefulness of the survival model. Third, maximum stratification of CSS can be achieved at the cutoff point of 0.33.

Conclusion

In the population-based study, LNR outperformed number-based LN variables for predicting CSS of node-positive penile cancer. The ratio-based prognostic factor stresses the important role of adequate LND and identification of metastatic LNs in the community setting.     

A new strategy to enhance artificial ligament graft osseointegration in the bone tunnel using hydroxypropylcellulose

Purpose

The aim of this study was to determine whether hydroxypropylcellulose (HPC) coating of polyethylene terephthalate (PET) artificial ligaments enhances graft osseointegration in the bone tunnel.

Methods

Thirty New Zealand white rabbits underwent artificial ligament graft transplantation in the bilateral proximal tibia tunnels. One limb was implanted with an HPC-coated PET graft, and the contralateral limb was implanted with a non-HPC-coated PET graft as a control. The rabbits were then randomly sacrificed at weeks four and eight after surgery for biomechanical testing, histological examination, and histomorphometric and real-time polymerase chain reaction analysis.

Results

At week four after surgery, there were no statistically significant differences in the load to failure or stiffness values between the experimental and control limbs (P = 0.328 and P = 0.128, respectively). At week eight after surgery, the mean load to failure and stiffness value of the experimental limbs was higher than that of the control limbs (P < 0.001 and P = 0.018, respectively). At week eight after surgery, some protruding new bone tissue from the host bone to the graft was found in the HPC-coated group, while a thick fibrous tissue band was observed at the interface between the graft and the host bone in the control group. Histomorphometric analysis showed that the graft-bone interface width in the HPC-coated group was significantly narrower than that in the control group at week eight after surgery (P < 0.001). At weeks four and eight after surgery, the mRNA expression level of bone morphogenetic protein-2 in the HPC group was higher than that in the control group (P = 0.001 and P = 0.010, respectively). The mRNA expression level of osteopontin in the HPC group was higher than that in the control group only at week four after surgery (P = 0.032).

Conclusions

Our data show that an HPC coating on the surface of PET artificial ligament grafts may induce artificial ligament graft osseointegration in the bone tunnel.