title: Alkene isomerization-hydroarylation tandem catalysis: indole C2-alkylation with aryl-substituted alkenes leading to 1,1-diarylalkanes.
abstract: A cobalt-N-heterocyclic carbene catalyst generated from CoBr2 , imidazolium salt, and cyclohexylmagnesium bromide was found to promote the imine-directed C2-alkylation of indoles with nonconjugated arylalkenes through a tandem alkene isomerization-hydroarylation process, affording 1,1-diarylalkanes with exclusive regioselectivity. The feasibility of the tandem catalysis was demonstrated for allyl-, homoallyl-, and bishomoallylbenzene derivatives. The catalytic system is also applicable to a variety of β-substituted styrene derivatives. Mechanistic experiments using deuterium-labeled indole substrate and Grignard reagent provided insight into the cobalt-mediated C-H activation step, which likely involves exchange of the C2-hydrogen atom of the former and the β-hydrogen atoms of the latter.
authors.affiliation: Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore, Fax: (+65) 6791-1961.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yamakawa
authors.forename: Naohiko
authors.initials: N
authors.lastname: Yoshikai
keywords: CH functionalization; alkenes; alkylation; cobalt; indoles