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Efficient solution-phase protocols for the high-throughput synthesis of 6-(1,2,3-triazol-1-yl)-dihydropyrimidones are reported. The multistep sequence involves the initial bromination of dihydropyrimidones precursors (DHPMs, Biginelli compounds) at the C6-methyl position, using a recyclable polymer-supported brominating agent under rapid flow-through conditions (residence time of 1 min). The 6-bromomethyldihydropyrimidone intermediates were subsequently subjected to a microwave-assisted azidation step (25 min), providing the key 6-azidomethyldihydropyrimidone precursors. In the final step of the sequence, the azides were treated with terminal acetylenes under Cu(I) catalysis (azide-acetylene ligation, "click chemistry") to provide the target 6-(1,2,3-triazol-1-yl)-dihydropyrimidones in a regiospecific fashion (1,4-triazoles) in moderate overall yield utilizing controlled microwave irradiation (20 min). In total, a library of 27 compounds was prepared with 4 points of diversity. 相似文献
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Different scavenging techniques using polymer-supported sequestration agents are described for the purification steps in the synthesis of N3-acylated dihydropyrimidines. For scavenging both excess anhydride and unwanted byproducts, polystyrene and silica supported diamines, aminomethyl-functionalized SynPhase Lanterns and diethylenetriamine StratoSpheres Plugs are used. In both synthesis and purification microwave flash heating was utilized, reducing reaction times from hours to minutes. These two steps coupled with an efficient solid-phase extraction (SPE) workup allowed the generation of a 28-member library of N3-acylated dihydropyrimidines using anhydrides. Using related protocols a 15-member library of N3-functionalized dihydropyrimidines utilizing acid chlorides as acylating reagents was also obtained. 相似文献
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T.?RublackEmail author S.?Hartnauer P.?Kappe C.?Swiatkowski G.?Seifert 《Applied Physics A: Materials Science & Processing》2011,103(1):43-50
The selective ablation of thin (∼100 nm) SiO2 layers from silicon wafers has been investigated by applying ultra-short laser pulses at a wavelength of 800 nm with pulse
durations in the range from 50 to 2000 fs. We found a strong, monotonic decrease of the laser fluence needed for complete
ablation of the dielectric layer with decreasing pulse duration. The threshold fluence for 100% ablation probability decreased
from 750 mJ/cm2 at 2 ps to 480 mJ/cm2 at 50 fs. Significant corruption of the opened Si surface has been observed above ∼1200 mJ/cm2, independent of pulse duration. By a detailed analysis of the experimental series the values for melting and breaking thresholds
are obtained; the physical mechanisms responsible for the significant dependence on the laser pulse duration are discussed. 相似文献
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The palladium-catalyzed arylation of rac-(E)-3-acetoxy-1,3-diphenylprop-1-ene with arylboronic acids was studied under controlled microwave irradiation conditions. A variety of different catalysts, bases, and solvents were explored in order to achieve optimum yields in the shortest possible reaction times. The best isolated yields were obtained using Pd2(dba)3·CHCl3/PPh3 as the catalytic system, potassium phosphate monohydrate as the base, and toluene/H2O as a solvent system. Microwave irradiation using 5 mol % of the palladium catalyst for 90 s (max. temp 170 °C) generally afforded the cross-coupling products in good to excellent yields. 相似文献
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Van Der Eycken E Appukkuttan P De Borggraeve W Dehaen W Dallinger D Kappe CO 《The Journal of organic chemistry》2002,67(22):7904-7907
Inter- and intramolecular hetero-Diels-Alder reactions in a series of functionalized 2(1H)-pyrazinones were investigated under controlled microwave irradiation. The cycloaddition reactions were efficiently performed in sealed tubes, utilizing either a combination of 1,2-dichloroethane and a thermally stable ionic liquid, or 1,2-dichlorobenzene as reaction medium. In all cases, a significant rate-enhancement using microwave flash heating as compared to thermal heating was observed. 相似文献
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