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71.
Francis J. Chung 《Journal of Fourier Analysis and Applications》2015,21(3):628-665
We show that measurements of a Neumann-to-Dirichlet map, with either inputs or outputs restricted to part of the boundary, can determine an electric potential on that domain. Given a convexity condition on the domain, either the set on which measurements are taken, or the set on which input functions are supported, can be made to be arbitrarily small. The result is analogous to the result by Kenig, Sjöstrand, and Uhlmann for the Dirichlet-to-Neumann map. The main new ingredient in the proof is an improved Carleman estimate for the Schrödinger operator with appropriate boundary conditions. This is proved by Fourier analysis of a conjugated operator along the boundary of the domain. 相似文献
72.
Saeromi Chung Mahmood H. Akhtar A. Benboudiaf Deog‐Su Park Yoon‐Bo Shim 《Electroanalysis》2020,32(3):520-527
An electrochemical sensor based on the conducting polymer composite with a palladium complex (Pd(C2H4N2S2)2) was developed for the detection of serotonin and dopamine simultaneously in the breast cancer cell and human plasma samples. The proposed sensor was fabricated using the Pd(C2H4N2S2)2 complex‐anchored poly2,2 : 5,2‐terthiophene‐3‐(p‐benzoic acid) (pTBA) layer on the AuNPs decorated reduced graphene oxide (AuNPs@rGO) substrate, which revealed the enhanced anodic current of the target species. The sensor probe was characterized by electrochemical and surface analysis methods. The experimental parameters affecting the sensor performance were optimized, in terms of AuNPs@rGO concentration, the number of electropolymerization cycle for pTBA, immobilization time of Pd(C2H4N2S2)2, and pH. The dynamic ranges for serotonin and dopamine were obtained from 0.02 to 200 μM, and from 0.1 to 200 μM with the detection limit of 2.5, and 24.0 nM, respectively. The reliability of proposed sensor was evaluated using cancer cell lines for the clinical applications. 相似文献
73.
Wai Chung Fu Timothy F. Jamison 《Angewandte Chemie (International ed. in English)》2020,59(33):13885-13890
The deuteriodifluoromethyl group (CF2D) represents a challenging functional group due to difficult deuterium incorporation and unavailability of precursor reagents. Herein, we report the use of chlorodifluoromethane (ClCF2H) gas in the continuous flow deuteriodifluoromethylation and gem‐difluoroalkenylation of aldehydes. Mechanistic studies revealed that the difluorinated oxaphosphetane (OPA) intermediate can proceed via alkaline hydrolysis in the presence of D2O to provide α‐deuteriodifluoromethylated benzyl alcohols or undergo a retro [2+2] cycloaddition under thermal conditions to provide the gem‐difluoroalkenylated product. 相似文献
74.
Heung Jae Lee Dong Seok Kim Min Chul Suh Sang Chul Shim 《Journal of polymer science. Part A, Polymer chemistry》1996,34(16):3255-3261
2,4-Hexadiyn-1,6-diol (HDO) was polymerized on glass and silicon plates by chemical vapor deposition without transition metal catalysis to form homogeneous thin films. Structural properties of the films were investigated by FT-IR, UV-visible, Raman, x-ray diffraction, and XPS spectroscopic analyses. The structure of CVD-polymerized HDO (CVD-PHDO) films was different from that of metathesis polymerized HDO (metathesis-PHDO), showing a polyacene-based structure but no polyene structure with acetylenic side groups. © 1996 John Wiley & Sons, Inc. 相似文献
75.
Deok-Heon Kweon Su-Dong Cho Sung-Kyu Kirn Joo-Wha Chung Yong-Jin Yoon 《Journal of heterocyclic chemistry》1996,33(6):1915-1918
3,4,5-Trichloropyridazin-6-one, 3,4,5,6-tetrachloropyridzine and 4,5-dichloro-3-(N,N-dimethylamino)-pyridazin-6-one were synthesized from 4,5-dichloro-3-nitropyridazin-6-one and dimethylchloromethylene-ammonium chloride selectively. 相似文献
76.
Eun Kee Cho Phong K. Quach Yunfei Zhang Jae Hun Sim Tristan H. Lambert 《Chemical science》2022,13(8):2418
The use of hydrazine-catalyzed ring-closing carbonyl–olefin metathesis (RCCOM) to synthesize polycyclic heteroaromatic (PHA) compounds is described. In particular, substrates bearing Lewis basic functionalities such as pyridine rings and amines, which strongly inhibit acid catalyzed RCCOM reactions, are shown to be compatible with this reaction. Using 5 mol% catalyst loadings, a variety of PHA structures can be synthesized from biaryl alkenyl aldehydes, which themselves are readily prepared by cross-coupling.Hydrazine catalysis enables the ring-closing carbonyl–olefin metathesis (RCCOM) to form polycyclic heteroaromatics, especially those with basic functionality.Polycyclic heteroaromatic (PHA) structures comprise the core framework of many valuable compounds with a diverse range of applications (Fig. 1A).1 For example, polycyclic azines (e.g. quinolines) are embedded in many alkaloid natural products, including diplamine2 and eupolauramine3 to name just a few. These types of structures are also of interest for their biological activity, such as with the inhibitor of the Src-SH3 protein–protein interaction shown in Fig. 1A.4 Many nitrogenous PHAs are also useful as ligands for transition metal catalysis, as exemplified by the widely used ligand 1,10-phenanthroline.5 Meanwhile, chalcogenoarenes6 such as dinaphthofuran7 and benzodithiophene8 have attracted high interest for both their medicinal properties9 and especially for their potential use as organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), and organic field-effect transistors (OFETs).10 These and numerous other examples have inspired the development of a wide variety of strategies to construct PHAs.1,11–14 Although these approaches are as varied as the structures they target, the wide range of molecular configurations within PHA chemical space and the challenges inherent in exerting control over heteroatom position and global structure make novel syntheses of these structures a topic of continuing interest.Open in a separate windowFig. 1(A) Examples of PHAs. (B) RCCOM strategy for PHA synthesis. (C) Lewis base inhibition for Lewis acid vs. hydrazine catalyzed RCCOM. (D) Hydrazine-catalyzed RCCOM for PHA synthesis.One potentially advantageous strategy for PHA synthesis is the use of ring-closing carbonyl–olefin metathesis15 (RCCOM) to forge one of the PHA rings, starting from a suitably disposed alkenyl aldehyde precursor 2 that can be easily assembled by cross-coupling (Fig. 1B). In related work, the application of RCCOM to form polycyclic aromatic hydrocarbons (PAHs) was reported by Schindler in 2017.16 In this case, 5 mol% FeCl3 catalyzed the metathesis of substrates to form phenanthrenes and related compounds in high yields at room temperature. This method was highly attractive for its efficiency, its use of an earth-abundant metal catalyst, and the production of benign acetone as the only by-product. Nevertheless, one obvious drawback to the use of Lewis acid activation is that the presence of any functionality that is significantly more Lewis basic than the carbonyl group can be expected to strongly inhibit these reactions (Fig. 1C). Such a limitation thus renders this method incompatible with a wide swath of complex molecules, especially PHAs comprised of azine rings. This logic argues for a mechanistically orthogonal RCCOM approach that allows for the synthesis of PHA products with a broader range of ring systems and functional groups.We have developed an alternative approach to catalytic carbonyl–olefin metathesis that makes use of the condensation of 1,2-dialkylhydrazines 5 with aldehydes to form hydrazonium ions 6 as the key catalyst–substrate association step.17–19 This interaction has a much broader chemoorthogonality profile than Lewis acid–base interactions and should thus be much less prone to substrate inhibition than acid-catalyzed approaches. In this Communication, we demonstrate that hydrazine-catalyzed RCCOM enables the rapid assembly of PHAs bearing basic functionality (Fig. 1D).For our optimization studies, we chose biaryl pyridine aldehyde 7 as the substrate (20 salt 11 was also productive (entry 2), albeit somewhat less so. Notably, iron(iii) chloride generated no conversion at either ambient or elevated temperatures (entries 3 and 4). Trifluoroacetic acid (TFA) was similarly ineffective (entry 5). Meanwhile, a screen of various solvents revealed that, while the transformation could occur in a range of media (entries 6–9), THF was optimal. Finally, by raising the temperature to 90 °C (entry 10) or 100 °C (entry 11), up to 96% NMR yield (85% isolated yield) of adduct 8 could be obtained in the same time period.Optimization studiesa
Open in a separate windowaConditions: substrate 8 (0.2 mmol) and 5 mol% catalyst in 0.4 mL of solvent (0.5 M) in a 5 mL sealed tube were heated to the temperature indicated for 15 h. Yields were determined by 1H NMR using CH2Br2 as an internal standard.b2 equiv. of TFA was used.c85% isolated yield.Using the optimized conditions, we explored the synthesis of various PHAs (Fig. 2). In addition to benzo[h]isoquinoline (8), products 12 and 13 with fluorine substitution at various positions could be generated in good yields. Similarly, benzoisoquinolines 14 and 15 bearing electron-donating methoxy groups and the dioxole-fused product 16 were also accessed efficiently. Furthermore, a phenolic ether product 17 with a potentially acid-labile N-Boc group was generated in modest yield. We found that an even more electron-donating dimethylamino group was also compatible with this chemistry, allowing for the production of 18 in 68% yield. On the other hand, adduct 19 bearing a strongly electron-withdrawing trifluoromethyl group was isolated in only modest yield. The naphtho-fused isoquinoline 20 could be generated as well; however, 20 mol% catalyst was required to realize a 35% yield. The thiophene-fused product 21 was furnished in much better yield, also with the higher catalyst loading. Although not a heterocyclic system, we found that the reaction to form phenanthrene (22) was well-behaved, providing that compound in 83% yield. In addition, an amino-substituted phenanthrene 23 was also formed in good yield. Other thiophene-containing PAHs such as 24–26 were produced efficiently. On the other hand, adduct 27 was generated only in low yield. Naphthofuran (28), which is known to have antitumor and oestrogenic properties,21 was synthesized in good yield. Finally, pharmaceutically important structures such as benzocarbazole2229 and naphthoimidazole2330 could be accessed in moderate yields with increased catalyst loading.Open in a separate windowFig. 2Substrate scope studies for hydrazine 1-catalyzed RCCOM synthesis of polycyclic heteroaromatics. a Conditions: substrate and catalyst 1·(TFA)2 (5 mol%) in THF (0.5 M) were heated to 100 °C in a 5 mL sealed tube for 15 h. Yields were determined on purified products. b 20 mol% catalyst.We also examined the scope of the olefin substitution pattern ( Entry Substrate Time (h) Yield (%) 1 15 96 2 48 5 3b 48 27 4 48 54 5 48 64
Entry | Catalyst | Solvent | Temp. (°C) | 8 yield (%) |
---|---|---|---|---|
1 | 10 | THF | 80 | 67 |
2 | 11 | THF | 80 | 53 |
3 | FeCl3 | DCE | rt | 0 |
4 | FeCl3 | DCE | 80 | 0 |
5 | TFA | THF | 80 | 0b |
6 | 10 | i-PrOH | 80 | 31 |
7 | 10 | CH3CN | 80 | 28 |
8 | 10 | EtOAc | 80 | 26 |
9 | 10 | Toluene | 80 | 24 |
10 | 10 | THF | 90 | 87 |
11 | 10 | THF | 100 | 96c |