1,721,010 research outputs found
Synthesis of pyrazole C-nucleosides via Tin(IV) chloride-promoted reactions of beta-D-ribofuranosyl cyanide with beta-dicarbonyl compounds
No full text2,3,5-Tri-O-benzoyl-beta-D-ribofuranosyl cyanide reacts with methyl acetoacetate and diethyl malonate in the presence of stoichiometric amounts of SnCl4 to give a beta-D-ribofuranosyl-enaminoketoester and a beta-D-ribofuranosyl-enaminodiester, respectively. The beta-D-ribofuranosyl-enaminoketoester was debenzoylated, treated with 2,2-dimethoxypropane and tert-butyl-dimethylsilyl chloride to give the methyl 3-amino-3-(5'-O-tert-butyldimethylsilyl-2',3'-O-isopropylidene-beta-D-ribofuranosyl)-2-acetyl propanoate obtained in good yield together with small amounts of its alpha-anomer. The reactions of the beta-anomer with hydrazine, methyl- and phenylhydrazine carried out under controlled experimental conditions, afforded the pyrazole C-nucleosides in good yields as beta-anomers. (C) 2002 Elsevier Science Ltd. All rights reserved
The Michael reaction of N-cinnamoylazoles with phenols. A simple synthesis of 4-arylchroman-2-ones and 1-arylbenzo[f]chroman-3-ones
No full text4-Arylchroman-2-ones 3 and 1-arylbenzo[f]chroman-3- ones 6 have been prepared in moderate to good yields by reaction of dihydric or trihydric phenols with p-substituted N-cinnamoylazoles in dichloromethane under reflux in the presence of DBU
Chemoselective synthesis of pyrazole derivatives via beta-enamino keto esters
No full textbeta -Enamino keto ester (2a) reacts with hydroxylamine to give an isoxazole derivative (3). Compound (2a) reacts with hydrazine, alkyl- and arylhydrazines to give pyrazole derivatives (4a-e) as only reaction products. Methylation of compound (4a) afforded the two isomeric pyrazole derivatives (4b) and (5)
A facile synthesis of pyrazole, isoxazole and pyrimidine ortho-dicarboxylic acid derivatives via beta-enaminoketoesters
No full textbeta-Alkoxycarbonyl-beta-enaminoketoesters 1a,b react with hydrazines to give pyrazole ortho-dicarboxylic acid derivatives 3, 4 and 5. Similarly la reacts with hydroxylamine to give isoxazole 6 and with amidines and guanidine to give pyrimidine ortho-dicarboxylic acid monoesters 7a-c. The total or partial hydrolysis of selected heterocycles afforded the dicarboxylic acids 8, 9 and 10 and the dicarboxylic acid monoesters 11 and 12. (C) 1997 Elsevier Science Ltd
A new synthetic entry to 3-carboxamido-4-carboxylic acid derivatives of isoxazole and pyrazole
No full textEthyl 2-amino-3-methoxycarbonyl-4-oxo-2-pentenoate (3) reacts with hydroxylamine or hydrazines to give isoxazole and pyrazole ortho-dicarboxylic acid esters 4 and 5, respectively. Partial hydrolysis of diesters 4 and 5 afforded the corresponding dicarboxylic acid monoesters 6 and 7. Amidation of the intermediate acid chlorides 8,9 followed by hydrolysis of 4-methylesters 10,11 gave the title compounds 1 and 2, respectively
A new and efficient route to the synthesis of pyrazole and pyrimidine C-nucleoside derivatives
No full textA new route to the synthesis of pyrazole and pyrimidine C-nucleosides, involving as the key step a metal catalysed reaction of beta-D-ribofuranosyl ketoesters with alkyl cyanoformates, is described. 2,3,5-Tri-O-benzoyl-beta-D-ribofuranosyl cyanide (1) reacts with alpha-bromoesters, in the presence of zinc dust, to give beta-D-ribofuranosyl-enaminoesters 2 which are easily hydrolised to beta-ketoesters 3. The reactions of compounds 3 with alkyl cyanoformates, in the presence of catalytic amounts of [Cu(acac)(2)], afford C-glycosyl enaminoketosters 4. These compounds react with benzylhydrazine and acetamidine to give pyrazole and pyrimidine C-nucleosides 5 and 6 respectively. (C) 1998 Elsevier Science Ltd. All rights reserved
6-phenylpyrones and 5-methylchromones from Kenya aloe
No full textTwo new compounds, 10-O-β-D-glucopyranosyl aloenin (4) and 8-C-β-D-glucopyranosyl-7-O-methyl-(R)-aloesol (6), were isolated from a commercial sample of Kenya aloe together with the known products aloenin (2), aloenin 2′-p-coumaroyl ester (3), aloenin aglycone (1), orcinol and acetylorcinol. All structures were determined or confirmed by spectral analyses
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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