RESUMO
Various multi-substituted pyrido[1,2-a]pyrimidin-4-ones were synthesized via a one-pot tandem CuI-catalyzed C-N bond formation/intramolecular amidation reaction at 130 °C in DMF. This protocol features simple operation, broad substrate scope, good functional group tolerance and gram scale preparation, thus allowing practical and modular synthesis of pyrido[1,2-a]pyrimidin-4-ones from readily available 2-halopyridine and (Z)-3-amino-3-arylacrylate ester in good to excellent yields.
RESUMO
In this work, we prepared polyhydroxylated lignin by demethylation and hydroxylation of lignin, and grafted phosphorus-containing groups by nucleophilic substitution reaction, the resulting material could be used as a carrier for the preparation of heterogeneous Cu-based catalysts (PHL-CuI-OPR2). The optimal PHL-CuI-OPtBu2 catalyst was characterized by FT-IR, TGA, BET, XRD, SEM-EDS, ICP-OES, XPS. The catalytic performance of PHL-CuI-OPtBu2 in the Ullmann CN coupling reaction was evaluated using iodobenzene and nitroindole as model substrates under nitrogen atmosphere with DME and H2O as cosolvent at 95 °C for 24 h. The applicability of modified lignin-supported copper catalyst was investigated of various aryl/heteroaryl halides with indoles under optimal conditions, the corresponding products were obtained with high yield. Additionally, it could be easily recovered from the reaction medium by an easy centrifugation and washing.
Assuntos
Cobre , Lignina , Cobre/química , Espectroscopia de Infravermelho com Transformada de Fourier , CatáliseRESUMO
Passenger contact in public transit (PT) networks can be a key mediate in the spreading of infectious diseases. This paper proposes a time-varying weighted PT encounter network to model the spreading of infectious diseases through the PT systems. Social activity contacts at both local and global levels are also considered. We select the epidemiological characteristics of coronavirus disease 2019 (COVID-19) as a case study along with smart card data from Singapore to illustrate the model at the metropolitan level. A scalable and lightweight theoretical framework is derived to capture the time-varying and heterogeneous network structures, which enables to solve the problem at the whole population level with low computational costs. Different control policies from both the public health side and the transportation side are evaluated. We find that people's preventative behavior is one of the most effective measures to control the spreading of epidemics. From the transportation side, partial closure of bus routes helps to slow down but cannot fully contain the spreading of epidemics. Identifying "influential passengers" using the smart card data and isolating them at an early stage can also effectively reduce the epidemic spreading.
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An efficient synthesis of fused azapolycycles based on (benz)imidazole and pyridine scaffolds has been developed. In all cases, the first nucleophilic addition of (benz)imidazoles to alkynyl bromides in tert-pentyl alcohol can proceed in a stereoselective manner to provide (Z)-N-(1-bromo-1-alken-2-yl)benzimidazoles at 110 °C. Sequentially, these adducts containing alkenyl bromide can undergo Pd-catalyzed intermolecular C-H annulation in the presence of internal alkynes in dimethylacetamide, affording fluorescent (benz)imidazole-fused pyridines in good to high yields. These compounds generally exhibit blue or green fluorescences (454-503 nm for solution states and 472-506 nm for solid states), and the fluorescence quantum yields remained in 0.19-0.89 and 0.02-0.74 for solution and solid states, respectively.
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An efficient Pd(II)-catalyzed oxidative annulation of 2-hydroxynaphthalene-1,4-diones and internal alkynes has been developed with high step efficiency. A broad range of functional groups are compatible with this reaction, thus providing a new entry to diverse naphtho[2,3-b]furan-4,9-dione derivatives in good to high yields.
RESUMO
Starting from arylboronic acids and ester (Z)-3-aminoacrylates, one-pot syntheses of diverse indole-3-carboxylic esters have been described through copper(ii)-catalyzed sequential Chan-Lam N-arylation and cross-dehydrogenative coupling (CDC) reactions. The initial Chan-Lam arylation can proceed in DMF at 100 °C for 24 h to give ester (Z)-3-(arylamino)acrylate intermediates in the presence of Cu(OAc)2/tri-tert-butylphosphine tetrafluoroborate, a catalytic amount of myristic acid as the additive, KMnO4 and KHCO3. Sequentially, these in situ arylated intermediates can undergo an intramolecular oxidative cross-dehydrogenative coupling process in mixed solvents (DMF/DMSO = 2 : 1) at 130 °C to give C3-functionalized multi-substituted indole derivatives.
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An efficient palladium-catalyzed route for tandem synthesis of imidazole-fused polyheterocycles from 2-vinyl imidazoles and aryl halides is described. The sequentially accomplished process comprises intermolecular Heck arylation of 2-vinyl imidazoles followed by an intramolecular aerobic oxidative C-H amination reaction promoted by the same Pd catalyst. This Pd-catalyzed tandem approach offers a straightforward protocol for the assembly of benzimidazo/phenanthroimidazo[1,2-a]quinolines in moderate to high yields, serving as a useful tool for the discovery of fluorescent materials.
RESUMO
Multisubstituted indoles were synthesized via a one-pot tandem copper-catalyzed Ullmann-type C-N bond formation/intramolecular cross-dehydrogenative coupling process at 130 °C in DMSO. The methodology allows practical and modular assembly of indoles in good to excellent yields from readily available aryl iodides and enamines.