title: Ni(NHC)]-catalyzed cycloaddition of diynes and tropone: apparent enone cycloaddition involving an 8π insertion.
abstract: A Ni/N-heterocyclic carbene catalyst couples diynes to the C(α)-C(β) double bond of tropone, a type of reaction that is unprecedented for metal-catalyzed cycloadditions with aromatic tropone. Many different diynes were efficiently coupled to afford [5-6-7] fused tricyclic products, while [5-7-6] fused tricyclic compounds were obtained as minor byproducts in a few cases. The reaction has broad substrate scope and tolerates a wide range of functional groups, and excellent regioselectivity is found with unsymmetrical diynes. Theoretical calculations show that the apparent enone cycloaddition occurs through a distinctive 8π insertion of tropone. The initial intramolecular oxidative cyclization of diyne produces the nickelacyclopentadiene intermediate. This intermediate undergoes an 8π insertion of tropone, and subsequent reductive elimination generates the [5-6-7] fused tricyclic product. This initial product undergoes two competing isomerizations, leading to the observed [5-6-7] and [5-7-6] fused tricyclic products.
authors.affiliation: Department of Chemistry, University of Utah , 315 South 1400 East, Salt Lake City, Utah 84112-0850, United States.
authors.forename: Puneet
authors.initials: P
authors.lastname: Kumar
authors.forename: Ashish
authors.initials: A
authors.lastname: Thakur
authors.forename: Xin
authors.initials: X
authors.lastname: Hong
authors.forename: K N
authors.initials: KN
authors.lastname: Houk
authors.forename: Janis
authors.initials: J
authors.lastname: Louie
mesh_terms: D002384:Catalysis; D003500:Cyclization; D061565:Cycloaddition Reaction; D053280:Diynes / Q000138:chemical synthesis* / Q000737:chemistry*; D006571:Heterocyclic Compounds / Q000737:chemistry*; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D013237:Stereoisomerism; D013379:Substrate Specificity; D014334:Tropolone / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry
chemical_list: D053280:Diynes; D006571:Heterocyclic Compounds; C030011:carbene; D014334:Tropolone; C003730:tropone; D008697:Methane