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The conversion of 132(S/R)-hydroxy-chlorophyll (Chl) a to 132-demethoxycarbonyl-132-oxo-Chl a in a yield of 40%, utilizing a simple pyrolysis technique, is described. About 10% of the phytyl ester of Mg-purpurin-18 was formed as a side product. The completely assigned 1H and 13C NMR spectra are presented for 132-demethoxycarbonyl-132-oxo-Chl a and a likely mechanism for its formation is proposed. A slight extension of this mechanism also explains the formation of the Mg-purpurin-18 side product. The proposed mechanism has several features comparable with those previously suggested for the allomerization of 132(R/S)-Chl a. Attempts to apply the same pyrolysis method to prepare 132-demethoxycarbonyl-132-oxo-Chl b from 132(S/R)-hydroxy-Chl b were unsuccessful. 相似文献
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A range of N-alkoxycarbonyl- and N-carboxamido-oxaziridines has been prepared to test the effects of oxaziridine structure on yields of enolate amination product. Side-products arising from reaction of aldehyde-derived oxaziridines with base were identified, while a ketone-derived oxaziridine afforded moderate yields of amination product with stabilised carbanions. 相似文献
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Jiali Gao 《Journal of Molecular Structure》1996,370(2-3):203-208
Ab initio molecular orbital calculations and statistical Monte Carlo simulations employing a combined quantum and molecular mechanical potential were used to determine the enol contents of acetic acid and the acetate ion in aqueous solution. A pKE of 19.3 ± 0.3 was predicted for the keto-enol equilibrium of acetic acid, and 21.8 ± 0.8 for the acetate ion in water. The results are found to be in good accord with Guthrie's calculations based on disproportionation reactions and kinetic data. Combining with the experimental pKa value of acetic acid, we obtained pKak = 26.6 for ionization of acetic acid as a carbon acid in water, and pKaE = 7.3 for ionization of the enol of acetic acid. 相似文献
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A new tandem catalysis strategy that transforms alkyne derivatives to (E)-enol-equivalents followed by stereoselective anti-selective aldol coupling or syn-selective [3,3]-rearrangement transformations is reported. The mechanism is thought to proceed through an interchanging series of Lewis acid and Brønsted acid catalyzed reactions via the intermediacy of a ketiminum ion species. 相似文献
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《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(3):874-878
We report the development of a Pd‐catalyzed process for the cross coupling of unactivated primary, secondary, and tertiary alkylcarbastannatrane nucleophiles with acyl electrophiles. Reactions involving optically active alkylcarbastannatranes occur with exceptional stereofidelity and with net retention of absolute configuration. Because the stereochemistry of the resulting products is entirely reagent‐controlled, this process may be viewed as a general, alternative approach to the preparation of products typically accessed via asymmetric enolate methodologies. Additionally, we report a new method for the preparation of optically active alkylcarbastannatranes, which should facilitate their future use in stereospecific reactions. 相似文献
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Enolates derived from α-(ortho-haloaryl)-substituted ketones undergo palladium-catalysed C-O bond formation to deliver benzofuran products in good yield. A catalyst generated from Pd2(dba)3 and the ligand DPEphos effects the key bond formation to deliver a variety of substituted products from both cyclic and acyclic precursors. The analogous thio-ketones undergo C-S bond formation using identical reaction conditions and are converted to benzothiophene products. A cascade sequence that produces the required α-aryl ketones in situ has also been developed, although the substrate scope is more restricted. 相似文献
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