Two-step Access Research Articles

Two-step access to bis-meso-perfluoroalkyl-corroles towards meso-perfluoroacyl-ABC-corroles.

A solventless and acid-catalyzed condensation of meso-perfluoroalkyl-dipyrromethanes with selected benzaldehydes was used to prepare ten different bilanes that were isolated before their oxidation into trans-A2B-corroles bearing two meso-perfluoroalkyl groups. Macrocycles bearing long chains (C3F7 or C7F15) are key precursors to afford ABC-corroles having a meso-acyl substituent when subjected to a mild and basic hydrolysis affecting one of the alkyl substituents.

A two-step access to fused-/spiro-polycyclic frameworks via double Heck cascade and acid-driven processes.

This report illustrates the rapid construction of two divergent classes of polycyclic frameworks, benzo[a]fluorenones and spiro-chromenone indenes, via a double Heck cascade and an acid-driven cyclization from easily accessible precursors, alkyl 2-bromocinnamate esters and diphenylacetylenes. The present strategy has surveyed a broad substrate scope and delivered an array of products with interesting structural features. Besides, fluorescence studies were performed for the synthesized benzo[a]fluorenones.

Catalysis enabled synthesis, structures, and reactivities of fluorinated S8-corona[n]arenes (n = 8-12).

Previously inaccessible large S8-corona[n]arene macrocycles (n = 8-12) with alternating aryl and 1,4-C6F4 subunits are easily prepared on up to gram scales, without the need for chromatography (up to 45% yield, 10 different examples) through new high acceleration SNAr substitution protocols (catalytic NR4F in pyridine, R = H, Me, Bu). Macrocycle size and functionality are tunable by precursor and catalyst selection. Equivalent simple NR4F catalysis allows facile late-stage SNAr difunctionalisation of the ring C6F4 units with thiols (8 derivatives, typically 95+% yields) providing two-step access to highly functionalised fluoromacrocycle libraries. Macrocycle host binding supports fluoroaryl catalytic activation through contact ion pair binding of NR4F and solvent inclusion. In the solid-state, solvent inclusion also intimately controls macrocycle conformation and fluorine-fluorine interactions leading to spontaneous self-assembly into infinite columns with honeycomb-like lattices.

A Two-Step Handover Strategy for GEO/LEO Heterogeneous Satellite Networks Based on Multi-Attribute Decision Making

Low Earth Orbit (LEO) satellites can provide high-speed and low-delay services for terrestrial users; however, the rapid movement of LEO satellites and the insufficient size of the LEO constellations incurs the instability of the transmission links. The rapid movement of LEO satellites also leads to frequent handovers. Fortunately, GEO/LEO heterogeneous satellite systems can remedy this shortcoming. As the handover decision strategy which makes the selection among the available satellites will directly impact the performance of GEO/LEO heterogeneous satellite systems, we propose a two-step access and handover decision strategy for heterogeneous satellite networks in this paper. Firstly, a GEO/LEO network selection is carried out based on utility functions that reflect user’s QoS requirements. Then, the multi-attribute decision making (MADM) method is used to select the specific LEO satellite if users select LEO satellite network. We also propose an Importance-TOPSIS scheme to improve the weight setting for handover attributes. Simulation results show that the proposed method can reduce the number of handovers and the forced termination probability of the system, and the overall throughput of the system is also improved.

Selective preparation of tetrasubstituted fluoroalkenes by fluorine-directed oxetane ring-opening reactions.

The selective ring-opening reaction of fluoroalkylidene-oxetanes was directed by the presence of the fluorine atom, enabling a two-step access to tetrasubstituted fluoroalkenes with excellent geometry control. Despite its small van der Waals radii electronic, rather than steric influences of the fluorine atom governed the ring-opening reaction with bromide ions, even in the presence of bulky substituents.

Ultrafine and highly-dispersed bimetal Ni2P/Co2P encapsulated by hollow N-doped carbon nanospheres for efficient hydrogen evolution

Ultrafine Ni2P/Co2P nanoparticles encapsulated in hollow porous N-doped carbon nanospheres are synthesized through a facile two-step access. Firstly, metallic Ni and Co coated by hollow N-doped spheres as precursors are obtained through a high temperature calcination route of organic polymer and inorganic Ni and Co salts. Then bimetal Ni2P/Co2P supported on N-doped carbon nanospheres are acquired by a facile phosphorization process. It is worth to note that aniline-pyrrole polymer can prevent fast growth and severe aggregation of Ni2P/Co2P, which implies more exposed active sites. Moreover, the calcination of hollow polymer spheres lead to the formation of ultrathin NC shell on the surface of Ni2P/Co2P hybrids, which can tune electronic structures, improve the conductivity and protect active sites from corrosion in harsh conditions. When used as HER catalyst, it displays remarkable catalytic activity in both acidic and alkaline solutions, which needs an onset potential of only 164 mV and 168 mV, respectively. Therefore, this work may propose a new strategy to design unique inorganic-organic heterostructures to combine ultrafine metal phosphides with porous carbon for efficient HER.

Vanadium sulfides interwoven nanoflowers based on in-situ sulfurization of vanadium oxides octahedron on nickel foam for efficient hydrogen evolution

Novel vanadium sulfides interwoven nanoflowers supported on nickel foam (VO-S/NF) has been synthesized through a facile two-step access. Firstly, octahedron-structured vanadium oxides as precursor were anchored on the surface of NF (VO/NF) by a hydrothermal process. Secondly, in-situ sulfurization in H2S gas has been applied to prepare VO-S/NF. XRD shows that VO-S/NF sample is composed of mixture phases including VS and Ni3S2, implying the interface effect between VS and Ni3S2. SEM images demonstrate that octahedron-structured VO from VO/NF changed to VO-S interwoven nanoflowers on VO-S/NF, which are composed of vertical interwoven nanosheets. It can enlarge surface area to expose abundant active sites and facilitate mass and charge transportation. The electrochemical measurements display the enhanced HER activity of VO-S/NF requiring an overpotential of 165mV to deliver 10mAcm−2, which may be ascribed to the novel structure of VS interwoven nanosheets and the synergistic effect between VS and Ni3S2. Furthermore, VO-S/NF remains high HER activity for at least 10h with excellent structural stability confirmed by post-HER characterization such as XRD, SEM and XPS. Therefore, it may provide a new way to design multiple transition metal sulfides-based electrocatalysts with unique nanostructure as well as interface effect for HER in alkaline.

Mobile Myanmar: The development of a mobile app culture in Yangon

This article looks at the unfolding smartphone app adoption culture in Yangon, Myanmar with insights from 18 informant interviews, 3 informal interviews, and nonparticipant observation. Through the domestication framework and actor-network theory, findings showed a unique overlay of actors influencing acquisition and adoption of apps, including: dependent users, “warm-gatekeepers,” mobile phone shops, and Facebook. Mediators such as Android skins, language skills, and other factors (mobile data pricing and network infrastructure) impact the relationships between these actors. Together, the impact of mediators on actor relationships highlighted a filtered means many users adopted to acquire new apps, a “two-step access” model of acquisition. This article traces how users acquire apps given this network of actors, following their journey and how they overcome challenges and limitations in their social and technological landscape.

Benzothiophene or benzofuran bridges in diaryl ethenes: two-step access by pd-catalyzed C-H activation and theoretical/experimental studies on their photoreactivity.

A series of terarylenes incorporating benzothiophene (BT)/benzofuran (BF) as the central ethene unit was synthesised by using sequential Pd-catalysed C-H activation reactions. This new methodology allows the easy modification of the nature of the pendant heteroarene groups. Diaryl ethene (DAE) derivatives with thiophene, thiazole, pyrrole, isoxazole and pyrazole rings were prepared. A large number of asymmetrical DAEs are easily accessible by this new method in both the BT and BF series. The study of their photochromic properties in solution revealed that the nature of the heteroarene and of the central unit drastically modify their photochromic behaviour. TD-DFT calculations were performed to assess the nature of the relevant excited states.

Chemical Tailoring of Teicoplanin with Site-Selective Reactions

Semisynthesis of natural product derivatives combines the power of fermentation with orthogonal chemical reactions. Yet, chemical modification of complex structures represents an unmet challenge, as poor selectivity often undermines efficiency. The complex antibiotic teicoplanin eradicates bacterial infections. However, as resistance emerges, the demand for improved analogues grows. We have discovered chemical reactions that achieve site-selective alteration of teicoplanin. Utilizing peptide-based additives that alter reaction selectivities, certain bromo-teicoplanins are accessible. These new compounds are also scaffolds for selective cross-coupling reactions, enabling further molecular diversification. These studies enable two-step access to glycopeptide analogues not available through either biosynthesis or rapid total chemical synthesis alone. The new compounds exhibit a spectrum of activities, revealing that selective chemical alteration of teicoplanin may lead to analogues with attenuated or enhanced antibacterial properties, in particular against vancomycin- and teicoplanin-resistant strains.

A simple two-step access to diversely substituted imidazo[4,5-b]pyridines and benzimidazoles from readily available 2-imidazolines

Abstract We discovered a facile rearrangement of N -(hetero)aryl 2-imidazolines into diversely substituted imidazo[4,5- b ]pyridines and benzimidazoles, under Bechamp reduction conditions. Combined with the earlier reported protocol for Pd-catalyzed (hetero)arylation of 2-imidazolines, it provides a simple two-step access to a range of compounds based on these medicinally important heterocyclic cores.

Efficient two-step access to azafluorenones and related compounds

Crystals of a lithiocuprate prepared from copper(I) chloride and lithium 2,2,6,6-tetramethylpiperidide (2equiv) were isolated and analyzed by X-ray diffraction as (TMP)2Cu(Cl)Li2·THF. The observation of this species is consistent with its having a role in deprotocupration–aroylation. Phenyl pyridyl ketones, phenyl quinolyl ketones, and phenyl thienyl ketones were prepared in tetrahydrofuran using the lithiocuprate and aroyl chorides as electrophiles. Diaryl ketones bearing a chloro group at the 2 position (of a pyridyl or phenyl group) thus synthesized were next converted through palladium-catalyzed ring closure to polycycles of the 5H-indeno[1,2-b]pyridin-5-one, 11H-indeno[1,2-b]quinolin-11-one, 9H-indeno[2,1-c]pyridin-9-one, and 8H-indeno[2,1-b]thiophen-8-one families.

Comparative analysis of endoscopic precut conventional and needle knife sphincterotomy

To compare the efficacy, complications and post-procedural hyperamylasemia in endoscopic pre-cut conventional and needle knife sphincterotomy. We performed a retrospective analysis of two pre-cut sphincterotomy (PS) techniques, pre-cut conventional sphincterotomy (PCS), and pre-cut needle knife (PNK). The study included 143 patients; the classic technique was used in 59 patients (41.3%), and the needle knife technique was used in 84 patients (58.7%). We analyzed the efficacy of bile duct access, the need for a two-step procedure, the rates of complications and hyperamylasemia 4 h after the procedure, "endoscopic bleeding" and the need for bleeding control. Furthermore, to assess whether the anatomy of the Vater's papilla, indications for the procedure or the need for additional procedures could inform the choice of the PS method, we evaluated the additive hyperamylasemia risk 4 h after the procedure with respect to the above mentioned variables. The bile duct access efficacy with PNK and PCS was 100% and 96.6%, respectively, and the difference between the two groups was not significant (P = 0.06). However, the needle knife technique required two-step access significantly more often, in 48.8% vs 8.5% of cases (P < 0.0001). The only complication noted was post-ercp pancreatitis (PEP), which was observed in 4/84 (4.8%) and 2/59 (3.4%) patients submitted to PNK and PSC, respectively; the difference between the two procedures was not significant (P = 0.98). An analysis of other consequences of the techniques yielded the following results in the PNK and PCS groups: hyperamylasemia 4 h after the procedure > 80 U/L, 41/84 vs 23/59 (P = 0.32); hyperamylasemia 4 h after the procedure > 240 U/L, 19/84 vs 11/59 (P = 0.71); pancreatic pain, 13/84 vs 7/59 (P = 0.71); endoscopic bleeding, 10/84 vs 8/59 (P = 0.97); and the need for bleeding control, 10/84 vs 7/59 (P = 0.79). In the next part of the study, we analyzed the influence of the method chosen on the risk of hyperamylasemia with respect to an indication for endoscopic retrograde cholangiopancreatography, papillary anatomy and concomitant procedures performed. We determined that the hyperamylasemia risk was increased by more than threefold [odds ratio (OR) = 3.38; P = 0.027] after PCS in patients with a flat Vater's papilla and more than fivefold (OR = 5.3; P = 0.049) after the PNK procedure in patients who required endoscopic homeostasis. PCS and PNK do not differ in terms of efficacy or complication rates, but PNK is more often associated with the necessity for a two-step procedure.

Regio‐ and Stereoselective Synthesis of Cyclopentenones: Intermolecular Pseudo‐Pauson–Khand Cyclization

Doing the two step: A very simple two-step access to polysubstituted cyclopentenones from terminal alkynes, [M(CO)6], and bromoalkenes is described. This protocol is an alternative to the intermolecular Pauson–Khand reaction, and can be used with a variety of bromoalkenes. Moreover, the final quenching allows the installation of reactive electrophiles (E). The enantiopure product cyclopentenones can be synthesized with an all-carbon-substituted quaternary stereocenter.

ChemInform Abstract: Stereoselective Synthesis of Substituted 2‐(Z‐Styrylsulfonyl)‐1H‐imidazoles and Benzothiazole.

AbstractThe novel two‐step access to title compounds (IV) leads stereoselectively to the (Z)‐styrylthio derivatives (III) which can be oxidized with retention of the geometry.

Intramolecular Cyclizations of Co2(CO)6-Complexed Propargyl Radicals: Synthesis ofd,l- andmeso-1,5-Cyclodecadiynes

Intramolecular radical cyclizations of Co2(CO)6-complexed bis-propargyl alcohols 1−5 provide an easy, two-step access to the otherwise hardly accessible d,l- and meso-3,4-diaryl-1,5-cyclodecadiynes 21−25. The acid-induced generation of bis-cations 6−10 is followed by reduction with a 100-fold excess of zinc, generating key reactive intermediates, i.e. the cobalt-complexed bis-propargyl radicals 11−15. The substitution pattern (0-, 4-, 3,4-, 3,4,5-) and the nature of aromatic substituents (H, i-Pr, OMe) are found essential both to the diastereoselectivity of the process—with d,l:meso ratios varying from 54:46 to 80:20—and the isolability of individual stereoisomers. In particular, an accumulation of methoxy groups on the periphery of the aromatic rings facilitates separation in both intra- and intermolecular reactions. The observed disparity in the level of diastereoselection in intra- and intermolecular reactions is accounted for on the basis of conformational analysis, calculation data for cobalt-complexed propargyl radicals, and the concept of a CH/π coordination. The new knowledge thus acquired has a predicting power, allowing future substrates to be designed, both topologically and stereoelectronically, in a manner favoring either d,l or meso diastereomers.

1,3-Dipolar Cycloaddition of N-Substituted Dipolarophiles and Nitrones: Highly Efficient Solvent-Free Reaction

New isoxazolidines were synthesized in good to excellent yields by 1,3-dipolar cycloaddition of N-vinylamide dipolarophiles and nitrones. Strikingly, solvent-free conditions gave high conversion and yields, shortened reaction time, and minimized degradation products. N-Vinyloxazolidin-2-one and its analogues used in these cycloaddition reactions were conveniently prepared in excellent yields by a modified version of Buchwald's one-step copper-catalyzed vinylation using vinyl bromide. From the adducts, a two-step access to various unsymmetric aspartate derivatives was also described.

An unusual, mild and convenient one-pot two-step access to ( E)-stilbenes from hydroxy-substituted benzaldehydes and phenylacetic acids under microwave activation: a new facet of the classical Perkin reaction

A mild and convenient one-pot two-step synthesis of hydroxystilbenes with trans selectivity has been developed through a modified Perkin reaction between benzaldehydes and phenylacetic acids bearing 4- or 2-hydroxy substitution at the aromatic ring, in the presence of piperidine–methylimidazole and polyethylene glycol under microwave irradiation. The observation of a simultaneous condensation–decarboxylation leading to the unusual formation of hydroxystilbenes in lieu of α-phenylcinnamic acid reveals an interesting facet to the classical Perkin reaction. The developed protocol provides a green alternative to the prevalent methods employing a toxic decarboxylating agent in the form of quinoline/Cu salt, and the requirement for harsh protection–deprotection steps for the synthesis of hydroxylated stilbenes.

One-step percutaneous nephrolithotomy sheath versus standard two-step technique

Objectives Advances in technique and equipment have allowed urologists to perform percutaneous stone removal with increasing efficacy and decreasing complications. The procedure of choice for large renal calculi is percutaneous nephrolithotomy. At our institution, percutaneous access is achieved by a two-step process using either Amplatz dilators or placement of a high-pressure balloon catheter for tract dilation, followed by advancement of a sheath over the balloon. A novel device, the Pathway Access Sheath (PAS) has been developed that allows for balloon tract dilation and percutaneous access sheath placement in one simple step. Methods Our study population consisted of 21 patients, who were randomized to one of two arms. Of the 21 patients, 10 underwent standard two-step access using a high-pressure balloon catheter and 11 underwent percutaneous nephrolithotomy using the novel PAS. We compared the insertion time, blood loss, and cost between the two techniques. Results The average insertion time was shorter in the PAS group (3 minutes) compared with the high-pressure balloon catheter (5 minutes, 42 seconds); a difference that was statistically significant ( P <0.01). The estimated blood loss and cost were similar between the two groups. The increased sheath flexibility of the PAS was noted to be an advantage in some patients. Conclusions The results of our study have shown that a novel single-step renal access device is safe and efficacious and results in a shorter insertion time for percutaneous nephrolithotomy. Blood loss was less in the PAS group as well, although the difference was not statistically significant. Additional studies will establish whether this device will provide a new standard of obtaining renal access.

Catalytic Enantioselective Conjugate Addition of Carbamates.

AbstractFor Abstract see ChemInform Abstract in Full Text.