title: Enantioselective Formal [4+2] Cycloadditions to 3-Nitroindoles by Trienamine Catalysis: Synthesis of Chiral Dihydrocarbazoles.
abstract: The first enantioselective formal [4+2] cycloadditions of 3-nitroindoles are presented. By using 3-nitroindoles in combination with an organocatalyst, chiral dihydrocarbazole scaffolds are formed in moderate to good yields (up to 87%) and enantioselectivities (up to 97% ee). The reaction was extended to include enantioselective [4+2] cycloadditions of 3-nitrobenzothiophene. The reaction proceeds through a [4+2] cycloaddition/elimination cascade under mild reaction conditions. Furthermore, a diastereoselective reduction of an enantioenriched cycloadduct is presented. The mechanism of the reaction is discussed based on experimental and computational studies.
authors.affiliation: Department of Chemistry, Aarhus University, 8000, Aarhus C, Denmark.
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Chemistry, Aarhus University, 8000, Aarhus C, Denmark.
authors.forename: Fernando
authors.initials: F
authors.lastname: Tur
authors.affiliation: Department of Chemistry, Aarhus University, 8000, Aarhus C, Denmark.
authors.forename: Rune Pagh
authors.initials: RP
authors.lastname: Nielsen
authors.affiliation: Department of Chemistry, Aarhus University, 8000, Aarhus C, Denmark.
authors.forename: Hao
authors.initials: H
authors.lastname: Jiang
authors.affiliation: Department of Chemistry, Aarhus University, 8000, Aarhus C, Denmark.
authors.forename: Frank
authors.initials: F
authors.lastname: Jensen
authors.affiliation: Department of Chemistry, Aarhus University, 8000, Aarhus C, Denmark. kaj@chem.au.dk.
authors.forename: Karl Anker
authors.initials: KA
authors.lastname: Jørgensen
keywords: asymmetric catalysis; cycloaddition; heterocycles; organocatalysis; synthetic methods