Ni(NHC)]-catalyzed cycloaddition of diynes and tropone: apparent enone cycloaddition involving an 8? insertion.

ABSTRACT: A Ni/N-heterocyclic carbene catalyst couples diynes to the C(?)-C(?) 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 8? insertion of tropone. The initial intramolecular oxidative cyclization of diyne produces the nickelacyclopentadiene intermediate. This intermediate undergoes an 8? 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.

SUBMITTER: Kumar P 

PROVIDER: S-EPMC4291811 | biostudies-other | 2014 Dec

REPOSITORIES: biostudies-other