Wyniki wyszukiwania - Biblioteka Nauki

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Pochodne pirazolowe : wyzwanie współczesnej chemii akademickiej i przemysłowej

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Popielarska H. , Myka A. , Drabińska B. , Gruszeczka A. , Kruk J. , Kurczab R. , Kujawski J.

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2013

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tom T. 92, nr 6

905--914

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Synteza sześcioczłonowych azotowych związków heterocyklicznych w reakcjach cykloaddycji heterodienowej

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Bogdanowicz-Szwed K. , Krasodomska M.

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tom [Z] 52, 11-12

821--842

EN

In this article we describe new developments in the synthesisof nitrogen heterocycles by hetero-Diels-Alder reaction, covering the literature since 1990. A main point of the discussion is stereoselectivity of the reactions and the preparation of enantiopure compounds either by using dienes and dienophiles carrying a chiral auxiliary or by using Lewis acids. Six-member nitrogen-heterocyclic compounds can be obtained by cycloaddition of aza-1,3-butadienes with carbon dienophiles or by cycloaddition of electron-rich dienes with imines, iminiun ions and nitriles acting as dienophiles. 1-Aza-1,3-butadienes may react as electron-rich as well as electron-deficient dienes in normal cycloaddition or in the cycloaddition with inverse electron demand. E.g. N,N-dimethyl hydrazones prepared from a,b-unsaturated aldehydes 1 reactsmoothly in normal cycloaddition with electron deficient dienophile. However, N-acyl- and N-sulfonyl-imines of a,b-unsaturated aldehydes, e.g. 10, react as electron-deficient dienes in reaction with an inverse electrondermand. Similarly to 1-aza-, 2-aza-1,3-butadienes may react as electron-rich or as electron-deficient components upon appropriate substituation. A versatile approach to functionalized pyrimidines involves the reaction of 1,3-diaza-1,3-butadienes 60 with ketenes. Intramolecular cycloadditions of 1,3-diazadienes 71 efficiently vield complex polycyclic molecules. Theoretical and synthetical studies carried out by van der Plas et al., deal with intramolecular cycloaddition of 5(v-alkynyl)pyrimidines 77. The substrates initially formed bridged adducts, that upon heating release the fused pyridine derivatives and appropriate cyanides by retro Diels-Alder reaction. The second approach to construction of six-membered nitrogen-heterocyclenby Diels-Alder reaction consists in cycloaddition of electron-rich-dienes with iminesor nitriles, that act as dienophiles. Electron deficient imines, e.g. acyl- or sulfonylimines add to many 1,3-dienes in good yields affording tetrahydropyridines. The cycloadditions of nonactivated imines have been investigated with regard to the effects of electronically neutral substituents and the influence of Lewis acids, The recent work in this area deals with asymmetric induction in azadiene reaction. E.g. the utility of chiral imines derived from enantiopure amino acids 93 in cycloaddition with electron-rich diene in presence of Lewis acid lead to pyridone 95 with very good diastereoselectivity (95% de). Chiral Lewis acids were also used in order to carry out enantioselective Diels-Alder reactions starting from achiral substrates and chiral catalyst. E.g. the reaction of imine derived from 3-pyridineformaldehyde 106 and Danishefsky's diene 89 afforded the desired cyclaadduct 107 in high optical purity. Cyanides have been found to be less reactive than imines since the reactions require extremely high temperatures. However, sulfonyl nitriles 112 react with a variety of dienes under much milder conditions affording pyridine derivatives 114.

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Nowe N-tlenki aldimin jako prekursory związków heterocyklicznych o potencjalnej aktywności biologicznej

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Kula K. , Dresler E. , Demchuk O. M. , Jasiński R.

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2015

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tom T. 94, nr 8

1385-1387

PL

Zsyntezowano serię nowych N-alkilopodstawionych N-tlenków C-(9-antraceno)-imin. Strukturę związków potwierdzono na podstawie danych spektralnych.

EN

N-alkylhydroxyamines were condensed at room temp. With 9-anthracenecarbaldehyde to N-alkyl substituted C-(9-anthracene) imine-N-oxides. The yields of the reaction were 90.5; 94.0 and 67.5% for alkyl substituents Me, PhCH₂ and Bu, resp. The structure of the compds. was confirmed by spectral anal.

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Anion alkoksyallenowy w syntezie związków naturalnych i ich analogów

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Busiak B. , Utecht G. , Jasiński M.

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2016

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tom [Z] 70, 1-2

3--23

EN

Among diverse systems containing multiple bonds, cumulenes are recognized as the most reactive derivatives towards both nucleophilic and electrophilic agents, and for this reason, they are considered as important class of substrates for organic synthesis. Over the last three decades alkoxyallenes have been demonstrated as highly useful C3-building blocks for the construction of numerous N-, O-, and S-containing heterocycles, including enantiomerically pure compounds. Special attention has been paid to lithiated alkoxyallenes as suitable nucleophiles for the reactions with alkyl halides, strained heterocycles, carbonyl compounds and their derivatives. The presence of the allene unit in the initially formed adducts opens up several possibilities in the preparation of more complex systems. In this review, selected applications of lithiated alkoxyallenes in the synthesis of natural products and their analogues are discussed.

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Physiological characterization of carbazole degrading bacteria isolated from a former gasworks site

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Pasternak G. , Kołwzan B. , Bernard-Baures G. , Rybak J. , Mrozik A.

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tom Vol. 38, nr 2

121--126

EN

Heterocyclic compounds could remain in the environment as hazardous and resistant pollutants. The aim of this study was to determine the physiological features of Methylobacterium sp. GPE1 strain being able to degrade heterocyclic compounds. Ten various substrates (sugars, alcohols and acids) were used in this assay, for metabolic purposes and eight ones were used as a sole source of carbon and energy. The comparison of the results with data taken from the literature indicated that GPE1 could be a new species of Methylobacterium sp.