Mehanizam aromatizacije 4-supstituiranih-1,4-dihidropiridina

doctoral thesis

• Title (english): Mechanism of aromatization of 4-supstitued-1,4-dihydropiridines
• Author: Maja Regović
• Mentor: Mladen Litvić (mentor); MBZ: 249464
• Mentor: Vladimir Vinković (mentor); MBZ: 71214
• Committee member: Ines Primožič (predsjednik povjerenstva)
• Committee member: Mladen Litvić (član povjerenstva); MBZ: 249464
• Committee member: Marina Ilakovac Kveder (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Chemistry); Zagreb
• Defense date and country: 2016-10-18, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Chemistry; Organic Chemistry
• Universal decimal classification (UDC): 54 - Chemistry. Crystallography. Mineralogy

Abstract

Hantzschovom ciklizacijom pripravljen je niz 1,4-dihidropiridinskih spojeva (1,4-DHP) s različitim supstituentima na položajima 3, 4 i 5. Iz njih su sintetizirani određeni piridinski spojevi koji su korišteni kao standardi prilikom analize omjera dealkilnog i alkilnog produkta na položaju 4 visokodjelotvornom tekućinskom kromatografijom. Za reakciju aromatizacije 1,4-DHP ispitan je niz različitih reakcijskih uvjeta i oksidansa: metalni, tritilijev i tropilijev tetrafluoroborat, 2,3-diklor-5,6-dicijano-1,4-benzokinon i tetracijanoetilen. Primjenom različitih spektroskopskih metoda je dokazano nastajanje kompleksa s prijenosom naboja prilikom prvog kontakta između 1,4-dihidropiridina i oksidansa. Na temelju dobivenih rezultata analize i detektiranih radikala, pretpostavljen je mehanizam kojim nastaje 4-dealkilni produkt u nekoliko uzastopnih koraka: početni korak je prijenos elektrona, zatim slijedi otcjepljenje karbokationa s položaja 4 pri čemu nastaje dihidropiridilni radikal, a potom prijenosom drugog elektrona i uklanjanjem protona s dušika nastaje piridinski produkt. Istim mehanizmom nastaje i 4-alkilni produkt, ali je drugi korak uklanjanje protona umjesto karbokationa. Kod tropilijevog kationa 4-alkilni produkt nastaje jednostupanjskim prijenosom hidrida, dok se kod tritilijevog kationa ne može jednoznačno odrediti nastaje li 4-alkilni produkt jednostupanjskim ili sekvencijalnim prijenosom hidrida.

Abstract (english)

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.

• Keywords: aromatizacija; dihidropiridilni radikal; 1; 4-dihidropiridin; kompleks s prijenosom naboja; mehanizam
• Keywords (english): aromatization; dihydropyridil radical; 1; 4-dihydropyridines; charge transfer complex; mechanism
• Language: croatian
• URN:NBN: urn:nbn:hr:217:713906
• Study programme: Title: Doctoral study in chemistry; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje prirodnih znanosti, polje kemija (doktor/doktorica znanosti, područje prirodnih znanosti, polje kemija)
• Type of resource: Text
• Extent: 192 str. ; 30 cm
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-02-06 11:09:36