title: Synthesis of pyrrolo[1,2-a]quinolines and ullazines by visible light mediated one- and twofold annulation of N-arylpyrroles with arylalkynes.
abstract: 1-(2-Bromophenyl)-1H-pyrrole and 1-(2,6-dibromophenyl)-1H-pyrrole react in the presence of catalytic amounts of rhodamine 6G () and N,N-diisopropylethylamine (DIPEA) under blue light irradiation with aromatic alkynes and subsequently cyclize intramolecularly to form pyrrolo[1,2-a]quinoline and ullazines. The reactions proceed at room temperature, avoid transition metal catalysts, and provide the target compounds in one pot in moderate to good yields. Mechanistic investigations suggest that the photo excited is reduced by DIPEA to form the corresponding radical anion , which is again excited by 455 nm light. The excited radical anion of donates an electron to the aryl bromide giving an aryl radical that is trapped by aromatic alkynes. The intermediate vinyl radical cyclizes intramolecularly and yields the product after rearomatization.
authors.affiliation: Institut für Organische Chemie, Universität Regensburg, Universitätsstraße 31, D-93053 Regensburg, Germany. Burkhard.Koenig@chemie.uni-regensburg.de.
authors.forename: Amrita
authors.initials: A
authors.lastname: Das
authors.affiliation: Institut für Organische Chemie, Universität Regensburg, Universitätsstraße 31, D-93053 Regensburg, Germany. Burkhard.Koenig@chemie.uni-regensburg.de.
authors.forename: Indrajit
authors.initials: I
authors.lastname: Ghosh
authors.affiliation: Institut für Organische Chemie, Universität Regensburg, Universitätsstraße 31, D-93053 Regensburg, Germany. Burkhard.Koenig@chemie.uni-regensburg.de.
authors.forename: Burkhard
authors.initials: B
authors.lastname: König