Synthesen mit Hilfe von Pyridiniumsalzen

Cleavage of N-phenylpyridinium or N-vinylpyridinium salts with secondary aliphatic amines leads to aromatic amino compounds or enamines which are often unobtainable by other routes. The other fragment, glutacondialdehyde or its rnonoanil, gives azulenes, as shown by Ziegler and Hafner, as well as Konig; these compounds can also be prepared from alkylpyridinium salts with cyclopentadienylsodium (Hafner). Syntheses of labile aldehydes which are otherwise dijjjcult to obtain and of a-ketocarboxylic acids, starting from pqiridinium salts and proceeding via nitrones or a-cyanoanils, are illustrated by many wcw examples. Benzimidazoles, benzothiazoles, and amidines are accessible from pyridinium salts via nitrones or a-cyanoanils; cyanoanils can be transformed into guinoxalines (including xanthopterine), perimidines, etc. Furthermore, nitrosonaphthols and nitrosonaphthylamines react with pyridinium salts containing an active iizethylene group on the nitrogq leading to new ring syslems. Further syn fhetic possihilities arise from nucleophilic &isplacements of the pyridine in pyriditiium salts by SN2 reactions. Combination of the route via nitrones with the methods of Arndt-Eistert, Ortoleva-King, or with chloromethylation constitutes a significant enlargement of its range of'application. The forniation of a-cyanoanils from diazoketones permits synthesis of a-keto-0-umino acids from a-amino acids, or of phenylglyoxylic acids from benzoic acids by chain extension.

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“…Thus, toluenes and benzyl halidesor their pyridinium saltscan be satisfactorily converted to benzoic acids, etc. [83]. .…”

Section: )mentioning

confidence: 99%

Syntheses Using Pyridinium Salts (IV)

Kröhnke

1963

Angew. Chem. Int. Ed. Engl.

129

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“…Then, using an adaptation of the Kröhnke method, we prepared five new 4,5-diazafluorenium-9-one salts by treating the 4,5-diazafluoren-9-one 1 with 2-bromo-4'-X-acetophenones ( Figure 1) in warm anhydrous acetone [14][15]. The novel N-[(4'-X-benzoyl)methyl]-9-oxo-4,5-diazafluorenium bromides 3a-e were characterized by chemical and spectral analyses.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of novel 4,5‐diazafluoren‐9‐one derivatives and theoretical study of 3+2 cycloaddition reactions

Danac

Druţă

Rotaru

et al. 2004

Journal of Heterocyclic Chem

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Some novel salts of 4,5-diazafluoren-9-one N-monosubstituted have been obtained by using Kröhnke method. The ability of 9-oxo-4,5-diazafluorenium phenacylides (as 1,3-dipoles) to react with activated symmetric dipolarophiles to give new heterocyclic compounds is presented. The new heterocyclic system of 10,10c-diazacyclopenta[c]fluoren-6-one is illustrated by a series of derivatives. The cycloaddition reaction proceeds, according to the semiempirical study, via a concerted nonsynchronous mechanism.

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“…27 The Kröhnke procedure [28][29][30] and sodium dithionite reduction [31][32][33] are examples of reactions involving addition of nucleophiles at g-position. The Kröhnke procedure, [28][29][30] consisting of base-catalysed reaction of ketones with alkyl or N-acyl pyridinium salts, was investigated years ago (Scheme 30). It is of particular synthetic interest since it constitutes a useful method of forming new carbon-carbon bonds to give g-substituted 1,4-dihydropyridines 95.…”

Section: Synthesis Of 14-dihydropyridinesmentioning

confidence: 99%

Synthesis, utility and medicinal importance of 1,2- & 1,4-dihydropyridines

2017

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Dihydropyridine (DHP) is among the most beneficial scaffolds that have revolutionised pharmaceutical research with unprecedented biological properties. Over the years, metamorphosis of easily accessible 1,2-and 1,4-dihydropyridine (1,4-DHP) intermediates by synthetic chemists has generated several drug molecules and natural products such as alkaloids. The 1,4-dihydropyridine (1,4-DHP) moiety itself is the main fulcrum of several approved drugs. The present review aims to collate the literature of 1,2-and the 1,4-DHPs relevant to synthetic and medicinal chemists. We will describe various methodologies that have been used for the synthesis of this class of compounds, including the strategies which can furnish enantiopure DHPs, either by asymmetric synthesis or by chiral resolution.We will also elaborate the significance of DHPs towards the synthesis of natural products of medicinal merit.

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Synthesen mit Hilfe von Pyridiniumsalzen

Cited by 191 publications

References 11 publications

Syntheses Using Pyridinium Salts (IV)

Syntheses Using Pyridinium Salts (IV)

Synthesis of novel 4,5‐diazafluoren‐9‐one derivatives and theoretical study of 3+2 cycloaddition reactions

Synthesis, utility and medicinal importance of 1,2- & 1,4-dihydropyridines

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