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121.
Tongcharoensirikul P Suarez AI Voelker T Thompson CM 《The Journal of organic chemistry》2004,69(7):2322-2326
Dimethyl thiophosphite (DMTP) was synthesized from dimethyl phosphite, and the diastereoselective addition of DMTP to benzaldimines bearing chiral auxiliary groups was examined. Yields of the product alpha-aminophosphonothionates ranged from 17% to 75% after chromatography. The addition of DMTP to the benzaldimine derived from (S)-phenylglycinol afforded the highest diastereoselectivity (83:17), whereas addition of DMTP to the benzaldimine derived from threonine methyl ester and alanine methyl ester were far less diastereoselective, affording 38:62 and 61:39 ratios, respectively. Addition of DMTP to the benzaldimine derived from (R)-alpha-methylbenzylamine (78:22) and (S)-serine methyl ester (73:27) were intermediate in selectivity. DMTP addition to the imines formed between serine methyl ester and acetaldehyde and isobutyraldehyde gave 55:45 and 70:30 ratios, respectively, with the diastereoselectivity corresponding roughly to the size of the alpha-alkyl group. The stereochemistry of the newly formed alpha-stereocenters resulting from the addition of DMTP to (S)- and (R)-phenylglycinol benzaldimines was confirmed by conversion of the product alpha-aminophosphonothionates to the known enantiomers of phosphonophenylglycine. 相似文献
122.
Über Thio-, Selenido- und Telluridogermanate (III): Zur Kenntnis von K6Ge2S6, K6Ge2Se6 und Na6Ge2Te6
On Thio-, Selenido-, and Telluridogermanates (III): K6Ge2S6, K6Ge2Se6, and Na6Ge2Te6 The new compounds K6Ge2S6 and K6Ge2Se6 crystallize in the monoclinic system, space group C2/m (No 12); lattice constants see “Inhaltsübersicht”. The compounds are isotypic and form the K6Si2Te6 structure. Na6Ge2Te6 crystallizes in the K6Sn2Te6 structure, monoclinic, space group P21/c (No 14); lattice constants see “Inhaltsübersicht”. 相似文献
123.
Conjugated β-fluoro-enamines 4 undergo cycloaddtion to methyl acrylate regio- and stereospecifically, affording the 1-fluorobicyclo[2.2.2]octan-2-one 6a after hydrolysis. 相似文献
124.
β-Alkoxy, β-dialkylamino, and β-N-alkylacylamino substituents determine the regioselectivity of the vinylic deprotonation of acrylic ester and nitrile derivatives: either α- or β-vinyllithium species may be generated. The corresponding acrylamides or systems with additional α-alkyl or α-methylmercapto substituents are lithiated at β-position. 相似文献
125.
Heike Wilhelm 《Tetrahedron》2006,62(29):6961-6966
8-Prenylnaringenin, a flavonoid, is the strongest known phytoestrogen (plant derived estrogen mimic) used in phytomedicinal applications. Starting from xanthohumol a byproduct of hops-extraction, 8-prenylnaringenin can be synthesized via isoxanthohumol. Of various demethylation procedures tested, the best yield (92%) is obtained by treatment with scandium trifluoromethanesulfonate and potassium iodide without any need of protection. The demethylation with AlBr3/collidine and of the TIPS protected isoxanthohumol provides good results too. 相似文献
126.
Volkmann M Whitehead K Rütters H Rullkötter J Gorbushina AA 《Rapid communications in mass spectrometry : RCM》2003,17(9):897-902
Microcolonial ascomycetes are known to inhabit bare rock surfaces in cold and hot deserts and thus are habitually exposed to high levels of solar radiation. Several of these stress-tolerant fungal isolates, cultivated in the laboratory under daylight illumination, were studied for the presence of effective UV-radiation protection substances. Liquid chromatography/mass spectrometry (LC/MS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) analyses allowed for efficient separation and structure clarification of two mycosporines. It was demonstrated that both mycosporine-glutamicol-glucoside and mycosporine-glutaminol-glucoside are natural and constitutive secondary metabolites of microcolonial fungi. The function and relation of these substances in the fungal cell are discussed. 相似文献
127.
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129.
Peter Gutsche Heike Schmitt Ulrich Haeberlen Tomasz Ratajczyk Slawomir Szymanski 《Chemphyschem》2006,7(4):886-893
(1)H NMR spectra of the methyl group in an oriented crystal sample of methylmalonic acid with all three non-methyl protons replaced by deuterons are interpreted in terms of the damped quantum rotation (DQR) theory of NMR line shapes. The DQR approach offers a perfect theoretical reproduction of the observed spectra while the conventional Alexander-Binsch line-shape model shows evident defects in the present case. The temperature trends of the quantities characterizing the coherent and incoherent dynamics of the methyl group in the DQR approach (the effective tunnelling frequency and two coherence-damping rates) derived from the spectra are fairly reproduced using a model reported previously. The present findings provide further evidence of limitations to the validity of the common belief that molecular rate processes in condensed phases are necessarily classical. 相似文献
130.
Summary Our multimethod enables the determination of pesticides adsorbed on soil particles up to 0.5 g/kg soil with recovery rates greater than 80%. 相似文献