title: Asymmetric hydrovinylation of vinylindoles. A facile route to cyclopenta[g]indole natural products (+)-cis-trikentrin A and (+)-cis-trikentrin B.
abstract: Vinylindoles undergo Ni(II)-catalyzed asymmetric hydrovinylation under very mild conditions (-78 °C, 1 atm ethylene, 4 mol % catalyst) to give the corresponding 2-but-3-enyl derivatives in excellent yields and enantioselectivities. Hydroboration of the alkene and oxidation to an acid, followed by Friedel-Crafts annulation, gives an indole-annulated cyclopentanone that is a suitable precursor for the syntheses of cis-trikentrins and all known herbindoles. For example, the cyclopentanone from 4-ethyl-7-vinylindole is converted into (+)-cis-trikentin A in four steps (Wittig reaction, alkene isomerization, diastereoselective hydrogenation, and nitrogen deprotection). The previous synthesis of this molecule from (S)-(-)-malic acid involved more than 20 steps and a preparative HPLC separation of diastereomeric intermediates.
authors.affiliation: Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, United States.
authors.forename: Wang
authors.initials: W
authors.lastname: Liu
authors.forename: Hwan Jung
authors.initials: HJ
authors.lastname: Lim
authors.forename: T V
authors.initials: TV
authors.lastname: RajanBabu
mesh_terms: D000475:Alkenes / Q000138:chemical synthesis / Q000737:chemistry; D001688:Biological Products / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D026121:Indole Alkaloids / Q000138:chemical synthesis* / Q000737:chemistry; D010084:Oxidation-Reduction; D013237:Stereoisomerism
chemical_list: D000475:Alkenes; D001688:Biological Products; D026121:Indole Alkaloids; C519345:trikentrin A; C506843:trikentrin B