title: Pyrrole versus quinoline formation in the palladium catalyzed reaction of 2-alkynyl-3-bromothiophenes and 2-alkynyl-3-bromofurans with anilines. A combined experimental and computational study.
abstract: Benzofuroquinolines were prepared by a new type of Pd catalyzed annulation reaction. In the first step, 2-alkynyl-3-bromobenzofurans were prepared by Sonogashira reactions of 2,3-dibromobenzofuran. Their Pd catalyzed reaction with electron-rich anilines afforded benzofuroquinolines by a domino C-N coupling/annulation process. This reaction proceeds as a C,N-cyclization via the nitrogen atom and the ortho-carbon of the aniline. Similarly, furoquinolines were prepared from 2,3-dibromofuran. In contrast, benzofuropyrroles and furopyrroles were formed by N,N-cyclization when electron-poor anilines were used. Earlier, we reported results related to the thiophene and benzothiophene series. Quinolines were formed from 2,3-dibromobenzothiophene when electron rich anilines were used. In contrast, pyrroles were obtained in the case of electron-poor anilines. On the other hand, pyrroles were generally obtained, not depending on the type of aniline, when 2,3-dibromothiophene was employed as the starting material. In the present article, a detailed DFT study related to the mechanism (quinoline versus pyrrole formation) is reported which provides a rationalization of the selectivities observed for the furan, benzofuran, thiophene and benzothiophene series and for the different selectivities observed for electron-rich and -poor anilines.
authors.affiliation: Institut für Chemie, Universität Rostock, Albert-Einstein-Str. 3a, 18059 Rostock, Germany.
authors.forename: Ghazwan Ali
authors.initials: GA
authors.lastname: Salman
authors.forename: Riffat Un
authors.initials: RU
authors.lastname: Nisa
authors.forename: Viktor O
authors.initials: VO
authors.lastname: Iaroshenko
authors.forename: Jamshed
authors.initials: J
authors.lastname: Iqbal
authors.forename: Khurshid
authors.initials: K
authors.lastname: Ayub
authors.forename: Peter
authors.initials: P
authors.lastname: Langer
mesh_terms: D000480:Alkynes / Q000737:chemistry*; D000814:Aniline Compounds / Q000737:chemistry*; D001966:Bromine / Q000737:chemistry*; D002384:Catalysis; D005663:Furans / Q000737:chemistry*; D015394:Molecular Structure; D010165:Palladium / Q000737:chemistry*; D011758:Pyrroles / Q000737:chemistry*; D011789:Quantum Theory; D011804:Quinolines / Q000737:chemistry*; D013876:Thiophenes / Q000737:chemistry*
chemical_list: D000480:Alkynes; D000814:Aniline Compounds; D005663:Furans; D011758:Pyrroles; D011804:Quinolines; D013876:Thiophenes; D010165:Palladium; D001966:Bromine; C023650:aniline