title: Photochemistry of 1,4-Dihydropyridine Derivatives: Diradical Formation, Delocalization and Trapping as a Route to Novel Tricyclic and Tetracyclic Nitrogen Heterocyclic Ring Systems.
abstract: Irradiation of an acetonitrile solution of 4-aryl-3,5-dibenzoyl-1,4-dihydropyridine derivatives 1a-c and maleimides 2a-c using medium pressure Hg-arc lamp (λ > 290) nm afforded three different cycloadducts 4, 5, 6 in addition to the oxidation products 3. These results indicate that compounds 1a-c undergoes intermolecular cycloaddition reaction through three biradical intermediates and behave photochemically different than those reported previously for the analogous 3,5-diacetyl and 3,5-dicarboxylic acid derivatives. The present work also offers simple access to novel tricyclic and tetracyclic nitrogen heterocyclic ring systems of potential biological and synthetic applications. The structure of the photoproducts was established spectroscopically and by single crystal X-ray crystallography.
authors.affiliation: Department of Chemistry, Faculty of Science, Kuwait University, P.O. Box 5969, Safat 13060, Kuwait. nader.aljalal@ku.edu.kw.
authors.forename: Nader A
authors.initials: NA
authors.lastname: Al-Jalal
authors.affiliation: Department of Chemistry, Faculty of Science, Kuwait University, P.O. Box 5969, Safat 13060, Kuwait. yehiaibrahim2002@yahoo.com.
authors.forename: Yehia A
authors.initials: YA
authors.lastname: Ibrahim
authors.affiliation: Department of Chemistry, Faculty of Science, Kuwait University, P.O. Box 5969, Safat 13060, Kuwait. n.alawadi@ku.edu.kw.
authors.forename: Nouria A
authors.initials: NA
authors.lastname: Al-Awadi
authors.affiliation: Department of Chemistry, Faculty of Science, Kuwait University, P.O. Box 5969, Safat 13060, Kuwait. maherriyad@hotmail.com.
authors.forename: Maher R
authors.initials: MR
authors.lastname: Ibrahim
authors.affiliation: Department of Chemistry, Faculty of Science, Kuwait University, P.O. Box 5969, Safat 13060, Kuwait. dr.osama_qc@yahoo.com.
authors.forename: Osama M
authors.initials: OM
authors.lastname: Sayed
mesh_terms: D018360:Crystallography, X-Ray; D061565:Cycloaddition Reaction; D004095:Dihydropyridines / Q000138:chemical synthesis / Q000737:chemistry*; D006575:Heterocyclic Compounds, 3-Ring / Q000737:chemistry; D006576:Heterocyclic Compounds, 4 or More Rings / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry; D055668:Photochemical Processes; D010777:Photochemistry
chemical_list: D004095:Dihydropyridines; D006575:Heterocyclic Compounds, 3-Ring; D006576:Heterocyclic Compounds, 4 or More Rings; C038806:1,4-dihydropyridine; D009584:Nitrogen
keywords: 1,4-dihydropyridines; 4,11-diazatetracyclo[5,3,1,02,6,08,10]undecane; dihydropyrrolo[3’,4’4,5]cyclopenta[1,2-b]-pyridine; photochemistry; tetrahydropyrrolo[3’,4’:5,6]pyrano[4,3-b]-pyridine