A full account of the total synthesis of (+)-cassaine ( 1) using the transannular Diels-Alder (TADA) reaction as the pivotal construction is described. The strategy began from Evans' oxazolidine 8, the only chiral source used for the total stereochemical outcome of the target molecule. The key intermediate 3 was obtained from 8 in 10 steps in 40% overall yield. Following extensive optimization, the coupling of 3 on both ends with another densely functional partner 2 followed by TADA reaction on macrocycle 4 cleanly furnished the tricycle 5. The stereochemical outcome in 5 was expected via a least-energetic transition state T4. A stereoselective reduction, hydroboration, and methyl cuprate 1,4-addition along with a few other functional interconversions transformed 5 into the key intermediate 37. Final tethering of dimethylaminoethyloxycarbonyl along with epimerization at C8 and alcohol deprotection at C3 yielded the natural product 1. 相似文献
The catalytic activity of a series of ruthenium(II) complexes in azide-alkyne cycloadditions has been evaluated. The [Cp*RuCl] complexes, such as Cp*RuCl(PPh 3) 2, Cp*RuCl(COD), and Cp*RuCl(NBD), were among the most effective catalysts. In the presence of catalytic Cp*RuCl(PPh 3) 2 or Cp*RuCl(COD), primary and secondary azides react with a broad range of terminal alkynes containing a range of functionalities selectively producing 1,5-disubstituted 1,2,3-triazoles; tertiary azides were significantly less reactive. Both complexes also promote the cycloaddition reactions of organic azides with internal alkynes, providing access to fully-substituted 1,2,3-triazoles. The ruthenium-catalyzed azide-alkyne cycloaddition (RuAAC) appears to proceed via oxidative coupling of the azide and alkyne reactants to give a six-membered ruthenacycle intermediate, in which the first new carbon-nitrogen bond is formed between the more electronegative carbon of the alkyne and the terminal, electrophilic nitrogen of the azide. This step is followed by reductive elimination, which forms the triazole product. DFT calculations support this mechanistic proposal and indicate that the reductive elimination step is rate-determining. 相似文献
An efficient one-pot synthesis of N-arylbenzamide is described via reaction of phenylboronic acid/aryl bromide with benzamide in the presence of CuI (5 mol%) as catalyst, 4-dimethylaminopyridine (20 mol%) as the ligand, and Cs2CO3 (2 mmol) as the base. This protocol was applied to synthesize a small library of N-arylbenzamide in high yields. 相似文献
A chemo-enzymatic synthesis of novel caged NAADP+ without the formation of multiple cage compounds has been achieved. The biological activity of the caged NAADP+ was demonstrated by its fast uncaging in intact sea-urchin eggs. 相似文献
l-Proline is utilized as an organocatalyst for the synthesis of substituted 2-aryl-2,3-dihydroquinolin-4(1H)-ones, in good yields. The efficiency of the catalyst was proved with a variety of substrates ranging from electron-deficient to electron-rich aryl aldehydes. 相似文献
Clostridium thermosuccinogenes are the only known anaerobic thermophilic bacteria that ferment inulin to succinate and acetate as major products and formate, lactate, and ethanol as minor products. In this study, organic acid production in 2-L fermentations having an initially low (−300 to −330 mV) or high (−220 to −250 mV) redox potential was compared for two strains of C. thermosuccinogenes (DSM 5808 and DSM 5809). Although DSM 5809 consistently provided higher succinate yield, high variability in results was attributed to the absence of redox control during the fermentations, and, therefore, fermentations at three controlled redox potentials (−240, −275, and −310 mV) were conducted. At an intermediate redox potential (−275 mV), the succinate yield was the greatest (0.36 g of succinate/g of hexose unit), whereas ethanol yield was the least (0.02 g/g). Redox potential did not significantly affect acetate or lactate formation. At controlled redox potential of −275 mV, the growth of DSM 5809 on three substrates was also compared: inulin, fructose, and glucose. DSM 5809 had similar growth rates when inulin (0.20/h) or glucose (0.21/h) was the carbon source but grew more slowly when fructose (0.16/h) was the carbon source. Also, the specific rate of utilization of fructose by DSM 5809 was higher (0.89 g of fructose/[g of biomass·h]) compared to glucose (0.53 g/[g·h]) or inulin (0.55 g/[g·h]). Succinate was the major product formed by DSM 5809 fermenting inulin (0.50 g/[g·h]) or glucose (0.36 g/[g·h]), and ethanol was the principal product when DSM 5809 fermented fructose (0.54 g/[g·h]). 相似文献
An unusual and unexpected synthesis of 3-(2-(arylamino)thiazol-4-yl)-2H-chromen-2-ones has been observed by the reaction of ethyl 2-(chloromethyl)-2-hydroxy-2H-chromene-3-carboxylate with various arylthioureas in ethanol under mild reaction conditions with excellent yields. The ambiguity in the structure of the obtained products has been solved by recording its single-crystal X-ray analysis. This protocol has been found to be a novel approach for the preparation of title compounds via benzopyran ring opening. A systematic plausible mechanism has been proposed for the formation of the product. Also, an efficient one-pot three-component method has been demonstrated for the formation of title compounds starting from salicylaldehyde.
The structures of two conformationally similar 1,4‐dihydropyrimidines with a novel carbamoyl substitution, viz. 6‐methyl‐5‐(N‐methylcarbamoyl)‐4‐phenyl‐1,2,3,4‐tetrahydropyrimidine‐2‐thione monohydrate, C13H15N3OS·H2O, (I), and 4‐(4‐chlorophenyl)‐6‐methyl‐5‐(N‐methylcarbamoyl)‐1,2,3,4‐tetrahydropyrimidine‐2‐thione monohydrate, C13H14ClN3OS·H2O, (II), exhibit the structural features of 1,4‐dihydropyridine calcium channel blockers. In both structures, the pyrimidine ring adopts a flattened boat conformation and the carbamoyl side chain is in an extended conformation with an anticlinal orientation. The phenyl ring occupies a pseudo‐axial position with respect to the pyrimidine ring in these structures. Both compounds crystallize with one molecule of water, which participates in a two‐dimensional hydrogen‐bonding network. The molecules are linked into dimers by N—H·S hydrogen bonds in both structures. 相似文献
Composite membranes with mordenite (MOR) incorporated in poly vinyl alcohol (PVA)–polystyrene sulfonic acid (PSSA) blend tailored with varying degree of sulfonation are reported. Such a membrane comprises a dispersed phase of mordenite and a continuous phase of the polymer that help tuning the flow of methanol and water across it. The membranes on prolonged testing in a direct methanol fuel cell (DMFC) exhibit mitigated methanol cross-over from anode to the cathode. The membranes have been tested for their sorption behaviour, ion-exchange capacity, electrochemical selectivity and mechanical strength as also characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. Water release kinetics has been measured by magnetic resonance imaging (NMR imaging) and is found to be in agreement with the sorption data. Similarly, methanol release kinetics studied by volume-localized NMR spectroscopy (point resolved spectroscopy, PRESS) clearly demonstrates that the dispersion of mordenite in PVA–PSSA retards the methanol release kinetics considerably. A peak power-density of 74 mW/cm2 is achieved for the DMFC using a PVA–PSSA membrane electrolyte with 50% degree of sulfonation and 10 wt.% dispersed mordenite phase. A methanol cross-over current as low as 7.5 mA/cm2 with 2 M methanol feed at the DMFC anode is observed while using the optimized composite membrane as electrolyte in the DMFC, which is about 60% and 46% lower than Nafion-117 and PVA–PSSA membranes, respectively, when tested under identical conditions. 相似文献