排序方式: 共有46条查询结果,搜索用时 31 毫秒
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Antti Pohjakallio Prof. Petri M. Pihko Ulla M. Laitinen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(37):11325-11339
The formation of 3‐unsubstituted 2‐isoxazolines by means of condensation reactions between α,β‐unsaturated aldehydes and oximes proceeds readily in the presence of catalytic amounts of anilinium salts. Mechanistically, the process involves a fast conjugate addition of the oxime and a slower intramolecular oxime‐transfer reaction. The rate of oxime transfer was found to correlate with the acidity of the catalyst. This finding enabled us to discover an enantioselective process in which the fragile conjugate‐addition product generated in the first stage is rapidly cyclized into the stable isoxazoline under acidic conditions, with conservation of enantiomeric excess. In summary, herein we describe synthetically useful protocols for accessing 3‐unsubstituted 2‐isoxazolines in both the enantioselective and racemic manner. The mechanism of the condensation reaction catalyzed by the anilinium salt was also investigated by NMR spectroscopy experiments in which the effect of differently substituted aldehydes and oximes as well as water on the reaction rate was studied. The results point to the rate‐limiting elimination of water from the 3‐hydroxy‐2‐isoxazolidine intermediate. 相似文献
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Alan Rigter Jan Priem Drophatie Timmers-Parohi Jan PM Langeveld Fred G van Zijderveld Alex Bossers 《BMC biochemistry》2009,10(1):29-16
Background
Molecular mechanisms underlying prion agent replication, converting host-encoded cellular prion protein (PrPC) into the scrapie associated isoform (PrPSc), are poorly understood. Selective self-interaction between PrP molecules forms a basis underlying the observed differences of the PrPC into PrPSc conversion process (agent replication). The importance of previously peptide-scanning mapped ovine PrP self-interaction domains on this conversion was investigated by studying the ability of six of these ovine PrP based peptides to modulate two processes; PrP self-interaction and conversion. 相似文献25.
Al-Hunaiti A Niemi T Sibaouih A Pihko P Leskelä M Repo T 《Chemical communications (Cambridge, England)》2010,46(48):9250-9252
In this study, we developed an efficient and selective iron-based catalyst system for the synthesis of ketones from secondary alcohols and carboxylic acids from primary alcohol. In situ generated iron catalyst of thymine-1-acetate (THA) and FeCl(3) under solvent-free condition exhibits high activity. As an example, 1-octanol and 2-octanol were oxidized to 1-octanoic acid and 2-octanone with 89% and 98% yields respectively. 相似文献
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Enantioselective iminium-catalyzed reactions with acrolein and methacrolein are rare. A catalytic enantioselective Mukaiyama-Michael reaction that readily accepts acrolein or methacrolein as substrates, affording the products in good yields and 91-97% ee, is presented. As an application of the methodology, an enantioselective route to the key C17-C28 segment of the pectenotoxin using the Mukaiyama-Michael reaction as the key step is described. 相似文献
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A rapid and extremely convenient method for alpha-methylenation of aldehydes with aqueous formaldehyde is described. Two optimal catalytic systems are presented that allow short reaction times and afford the functionalized products in good to excellent yields (up to 99%) and chemoselectivity. 相似文献
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