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Synthesis of Oxacyclic Scaffolds via Dual Ruthenium Hydride/Brønsted Acid‐Catalyzed Isomerization/Cyclization of Allylic Ethers
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Dr. Erhad Ascic Ragnhild G. Ohm Dr. Rico Petersen Dr. Mette R. Hansen Casper L. Hansen Daniel Madsen Prof. Dr. David Tanner Prof. Dr. Thomas E. Nielsen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(12):3297-3300
A ruthenium hydride/Brønsted acid‐catalyzed tandem sequence is reported for the synthesis of 1,3,4,9‐tetrahydropyrano[3,4‐b]indoles (THPIs) and related oxacyclic scaffolds. The process was designed on the premise that readily available allylic ethers would undergo sequential isomerization, first to enol ethers (Ru catalysis), then to oxocarbenium ions (Brønsted acid catalysis) amenable to endo cyclization with tethered nucleophiles. This methodology provides not only an attractive alternative to the traditional oxa‐Pictet–Spengler reaction for the synthesis of THPIs, but also convenient access to THPI congeners and other important oxacycles such as acetals. 相似文献
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An efficient and environmentally friendly synthesis of tetrahydro‐β‐carboline hydrochlorides via Pictet–Spengler reaction was described. Tryptamine hydrochlorides were used as the reactant and no additional acid catalyst was needed. This reaction was completed within 2.5–9 min in good yield. 相似文献
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Rémi Andres Fenggang Sun Dr. Qian Wang Prof. Dr. Jieping Zhu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(1):e202213831
We report herein an asymmetric Pictet–Spengler reaction of α-ketoesters. In the presence of a catalytic amount of simple alanine-derived squaramide and p-nitrobenzoic acid, reaction of tryptamines with methyl 2-oxoalkanoates afforded the corresponding 1-alkyl-1-methoxycarbonyl tetrahydro-β-carbolines (THBCs) in high yields and ee values. A primary kinetic isotope effect (KIE=4.5) using C2-deteurium-labelled tryptamine indicates that rearomatization through deprotonation of the pentahydro-β-carbolinium ion could be the rate- and enantioselectivity-determining step. A concise enantioselective total synthesis of (+)-alstratine A, a hexacyclic cagelike monoterpene indole alkaloid, featuring this reaction as a key step, was subsequently accomplished. Remeasurement of the [a]D value of the natural product indicates that natural alstratine A is dextrorotatory rather than levorotatory as it was initially reported in the isolation paper. 相似文献
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Jimei Zhou Chao Wang Dong Xue Weijun Tang Jianliang Xiao Chaoqun Li 《Tetrahedron》2018,74(49):7040-7046
Fe(OTf)2 has been found to be an efficient catalyst for the Oxa-Pictet–Spengler cyclization reaction leading to isochromans. A series of substituted isochromans were obtained with good to excellent isolated yields by coupling β-arylethanols with aldehydes or ketals under the catalysis of 1?mol% of Fe(OTf)2?at 70?°C. Using a cheap, less-toxic catalyst with water as the only byproduct, this iron-catalyzed Oxa-Pictet–Spengler reaction can be considered environmentally-friendly and atom-economic. 相似文献
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