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Non-asymmetric organocatalysis
No full textAsymmetric organocatalysis is now an established methodology for the preparation of chiral compounds. However, these are not the only valuable molecules which can be conveniently obtained. Organocatalytic reactions affording achiral compounds are gaining momentum, opening unexplored pathways in the synthesis of densely functionalized aromatic moieties, olefins and useful molecules such as natural substances
Design of experiments: a rational approach toward non-covalent asymmetric organocatalysis
Full text linkThis Account describes from a personal point of view the possible strategies to tackle and optimize non-covalent organocatalyzed reactions. When chemical intermediates are covalently bound, predictive mechanicistic pictures can be depicted. In contrast, there are several organocatalyzed transformations (e.g. those employing Cinchona alkaloids) for which optimization is essentially based on a trial-and-error approach. The experience of authors is that these reactions can be tackled with a rational approach employing DoE, Design of Experiment. This tool is widely exploited in industrial process chemistry, but little known within academia. The purpose of this Account is to show the effectiveness and utility of DoE in asymmetric non-covalently organocatalyzed reactions, discussing selected examples
Multicomponent asymmetric reactions mediated by proline lithium salt
No full textThe multicomponent reaction between proline lithium salt, 2-cyclohexen-1-one and aliphatic aldehydes affords the 4-alkylidene-2- cyclohexen-1-ones, which are interesting fragrances, and bicyclic amino acids that bear four additional stereocenters, obtained as single stereoisomer. © The Royal Society of Chemistry
Comments on the analysis interpretation by Rogers and Latendresse regarding samples coming from the Shroud of Turin
No full textThe presence of a “invisible mending” has been proposed as an explanation for medieval radiocarbon dating measurements made on the Shroud of Turin. Here we show that the chemical analysis which was to support this theory is not consistent, and no scientific data confirm these speculations. Specifically, the samples of the Shroud image fibers underwent a different cleaning procedure with regards to those
allegedly belonging to the medieval mending. There is no reliable indication of the supposedly diagnostic compounds (e.g. gum Arabic, pentoses). The only detectable difference between the samples is the presence of a compound with an aliphatic chain which cannot be identified more in detail, e.g. as sebum
There is no mass spectrometry evidence that the C14 sample from the Shroud of Turin comes from a "medieval invisible mending"
No full textThis is an editorial regarding a paper published on Thermochimica Acta (R.N. Rogers, Thermochimca Acta, 425 (2005) 189–194). A close-up analysis of the pyrolysis-mass spectra reported in the original paper reveals that the differences found between the samples coming from different parts of the Shroud are just due to the presence of a contaminant with a long aliphatic chain. Except for the presence of the
contaminant, the two pyrolysis-mass spectra look alike rather than different. Therefore, the pseudoscientific theory stating that the C14 sample might come from a “medieval invisible mending” remains unsupported by evidences
Improved asymmetric SNAr reaction of beta-dicarbonyl compounds catalyzed by quaternary ammonium salts derived from cinchona alkaloids
No full textEfficient preparation of 3-substituted furan-2(5H)-ones and their direct vinylogous aldol addition.
No full textOrganocatalytic regio- and asymmetric C-selective SNAr reactions-stereoselective synthesis of optically active spiro-pyrrolidone-3,3 '-oxoindoles
No full textThe first example of catalytic enantioselective nucleophilic aromatic substitution of -dicarbonyl compounds is presented. An O-benzoylated cinchona alkaloid derivative catalyst gave a selective C-arylation reaction compared to, e.g., the corresponding benzylated catalyst which provided a 1:1 mixture of the C- and O-arylation products. The reaction proceeds well for various aromatic compounds with different 1,3-dicarbonyl compounds, and the optically active products are obtained in very high yields and with up to 92% ee. One further scope of the organocatalytic enantioselective nucleophilic aromatic substitution reaction is demonstrated by the synthesis of the optically active spiro-pyrrolidone-3,3′-oxoindole structure. Copyright © 2005 American Chemical Society
“A Quantitative Measure of Borane Tert-Butylamine Complex Effectiveness in Carbonyl Reduction of Aged Papers.”
No full textAsymmetric construction of quaternary stereocenters by direct organocatalytic amination of alpha-substituted alpha-cyanoacetates and beta-dicarbonyl compounds.
No full textThe first organocatalytic highly enantioselective reactions of substituted alpha-cyanoacetates and beta-dicarbonyl compounds with azodicarboxylates are reported. In the presence of 0.1-5 mol % of a quinidine-derived alkaloid beta-ICD, optically active quaternary hydrazine adducts are obtained in very high yields and with enantioselectivities up to >98% ee. A two-step procedure for the cleavage of the hydrazine N-N bond using SmI2 is also demonstrated
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