Mechanism of aromatization of 4-supstitued-1,4-dihydropiridines

Regović, Maja (2016) Mechanism of aromatization of 4-supstitued-1,4-dihydropiridines. Doctoral thesis, Faculty of Science > Department of Chemistry.

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Abstract

1,4-Dihydropyridines with different substituents on positions 3, 4 and 5 were prepared using Hantzsch cyclisation reaction and corresponding pyridines were prepaired from them. The obtained compounds were used as standards in high perfomance liquid chromatography when analysing the ratio of alkylated and dealkylated product on position 4 resulted during aromatization. Many reaction conditions and oxidants were examined for aromatization of 1,4-DHP: metal, tropylium and trityl tetrafluoroborate, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and tetracyanoethylene. Using different spectroscopic methods charge transfer complexes during the first contact of 1,4-dihydropyridine and oxidant were identified. Based on obtained results of aromatization product analysis and radicals detected, a mechanism was proposed which explains the appearance of 4-dealkylated product via few consecutive steps: initial step is electron transfer, then carbocation elimination from position 4 to give dihydropyridil radical, which is followed by second electron transfer and losing a proton from nitrogen atom results in pyridine product. The same mechanism explains the appearance of 4-nondealkylated product, but the second step involves proton elimination instead of carbocation. When using tropylium cation 4-alkylated product results by one step hydride transfer. It can not be uniquely determined whether the 4-alkylated product results by one step or sequential hydride transfer when using trityl cation.

Item Type: Thesis (Doctoral thesis)
Keywords: aromatization, dihydropyridil radical, 1,4-dihydropyridines, charge transfer complex, mechanism
Supervisor: Litvić, Mladen and Vinković, Vladimir
Date: 2016
Number of Pages: 192
Subjects: NATURAL SCIENCES > Chemistry
Divisions: Faculty of Science > Department of Chemistry
Depositing User: Branka Maravic
Date Deposited: 14 Nov 2016 13:38
Last Modified: 14 Nov 2016 13:38
URI: http://digre.pmf.unizg.hr/id/eprint/5291

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