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Reductive One Batch Synthesis of N-Substituted Pyrrolidines from Primary Amines and 2,5-Dimethoxytetrahydrofuran
No full textThe construction of the pyrrolidine ring about a nitrogen of a primary amine by a reductive condensation reaction using 2,5-dimethoxytetrahydrofuran and sodium borohydride in acidic water medium is described. The reaction is fast, affords good to excellent yields and appears insensitive to electron effects and severe steric hindrance; it is found to be compatible with a large variety of aryl substituents, including nitro and oxo groups. The reaction allows the introduction of two deuterium atoms, with label conservation, in both the alpha-positions of the pyrrolidine ring by the use of sodium borodeuteride instead of sodium borohydride
Preparation, Properties, and Reductive Alkylation of Arylhydrazides
No full text1-Acyl-2-arylhydrazines (1), readily obtained in high yield from the condensation of arylhydrazines and the appropriate liquid carboxylic acid (2). underwent reductive alkylation with the same or different liquid carboxylic acids (2) and NaBH4 to give 1-acyl-2-alkyl-2-arylhydrazines (3) in good to moderate yields. The carbaxylic acid has both the role of supplying the entering alkyl group and of acting as solvent. Most likely, it also modifies the BH4- anion to an active reducing agent under those conditions. The H-1 NMR criteria for identifying the location of acylation of hydrazines and E and Z isomers are given. The MS spectra of the prepared hydrazides were analyzed in order to identify relevant structural features leading to specific fragmentations
1-Substituted 1,4,5,6-Tetrahydropyridazines and 1-(N-Substituted)aminopyrrolidines from Hydrazines and 2,5-Dimethoxytetrahydrofuran
No full textN-Substituted 1,4,5,6-tetrahydropyridazines ((3) under bar) can be prepared in a one pot procedure from a hydrazine (1) under bar) and 2,5-dimethoxytetrahydrofuran ((2) under bar) using NaBH4 in aqueous-THF acidic medium in fair yields. Variable amounts of two side products are also formed: hexahydropyridazines (5) under bar, likely produced by a route other than the direct reduction of (3) under bar and 1-aminopyrrolidines (4) under bar. A direct reduction-N-reductive ethylation of (3) under bar could be achieved in AcOH with NaBH4
New heterocycles from the reaction between some natural α-amino acid hydrazides and formaldehyde
No full textThe ring forming condensation between some natural α-amino acid phenylhydrazides (1) and aqueous formaldehyde (2) has opened a novel synthetic route to hexahydro-1,2,4-triazin-6-one derivatives (3). Polycyclic systems were obtained from the same reaction carried out with L-aspartic acid 1,4-bis(2-phenylhydrazide) (1d), L-histidine phenylhydrazide (1e) and L- tryptophan phenylhydrazide (1f) which gave perhydro-4,6-dioxo-2,8- diphenyl[1,2,4]triazino[4,5-d][1,2,4]triazepine (5) perhydro-1-oxo-3- phenylimidazo[5,4-d][1,2,4]triazino[4,5-a]pyridine (7) and 1,2,3-H-3-(2- phenylcarbazoyl)-β-carboline (8), respectively. Substrates 1 were conveniently obtained by direct reaction of phenylhydrazine with L-α-amino acid esters retaining the original chirality
Condensation Reaction Between α-Amino Acid Phenylhydrazides and Carbonyl Compounds
No full textThe natural α-amino acid phenylhydrazides 1a-d readily react with the aldehydes 2a-d and ketones 2e-h to produce the 3-(phenylamino)imidazolidin-4-one derivatives 4 in good yields. Their structures were confirmed by X-ray structural analysis. Polycyclic systems were obtained from the reaction of L-tryptophan phenylhydrazide (1d) and L-histidine phenylhydrazide (1e) with benzaldehyde (2c), which gave 1,10-diphenyl-2-(phenylamino)-2,9,10a-triazacyclopenta[b]fluoren-3-one (5dc) and 4,6-diphenyl-7-(phenylamino)-3,4,6,7,8a,9-hexahydro-8H-diimidazo [1,5-a:4′,5′-d]pyridin-8-one (5ec), respectively
Improved Method for the Analysis of Organic Acids and New Derivatization of Alcohols in Complex Natural Aqueous Matrixes: Application to Wine and Apple Vinegar
No full textAn improvement in the procedure for investigation of organic acids and a new derivatization method, amenable to gas chromatographic-mass spectrometric detection of alcohols, are presented. The latter is based on the formation of phenacetyl esters. The simultaneous application of the two methods also allows data to be obtained on some volatile neutrals. present in complex natural aqueous fluids. Application to wine and cider vinegars allowed detection of a number of previously unreported components, among which are interesting partially esterified polycarboxylic esters
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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