title: Unexpected imidazoquinoxalinone annulation products in the photoinitiated reaction of substituted-3-methyl-quinoxalin-2-ones with N-phenylglycine.
abstract: Photoinduced electron transfer between N-phenylglycine (NPG) and electronically excited triplets of 7-substituted-3-methyl-quinoxalin-2-ones in acetonitrile generate the respective ion radical pair, where by decarboxylation the phenyl-amino-alkyl radical, PhNHCH2•, is generated. This radical reacts with the 3-methyl-quinoxalin-2-ones ground states, leading to the product 2. Other, unexpected, 7-substituted-1,2,3,3a-tetrahydro-3a-methyl-2-phenylimidazo[1,5-a]quinoxalin-4(5H)-ones, annulation products, 3a-f, were generated; likely by the addition of two PhNHCH2• radicals, to positions 3 and 4 of the quinoxalin-2-ones. The reaction mechanism includes a photoinduced one electron transfer initiation step, propagation steps involving radical intermediates and NPG with radical chain termination steps that lead to the respective products 2a-f and 3a-f and NPG by-products. The proposed mechanism accounts for the strong dependency found for the initial photoconsumption quantum yields on the electron-withdrawing power of the substituent. Therefore, photolysis of common reactants widely used such as NPG and substituted quinoxalin-2-ones may provide a simple synthetic way to the unusual, unreported tetrahydro-imidazoquinoxalinones 3a-f.
authors.affiliation: Departamento de Química Orgánica y Fisicoquímica, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Santiago, Chile.
authors.forename: Julio R
authors.initials: JR
authors.lastname: De la Fuente
authors.forename: Álvaro
authors.initials: Á
authors.lastname: Cañete
authors.forename: Carolina
authors.initials: C
authors.lastname: Jullian
authors.forename: Claudio
authors.initials: C
authors.lastname: Saitz
authors.forename: Christian
authors.initials: C
authors.lastname: Aliaga
mesh_terms: D005998:Glycine / Q000031:analogs & derivatives* / Q000737:chemistry; D055668:Photochemical Processes; D066244:Proton Magnetic Resonance Spectroscopy; D011789:Quantum Theory; D011810:Quinoxalines / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D011810:Quinoxalines; C021316:N-phenylglycine; D005998:Glycine