title: Cobalt-catalyzed formal [4+2] cycloaddition of α,α'-dichloro-ortho-xylenes with alkynes.
abstract: A formal [4+2] cycloaddition of α,α'-dichloro-ortho-xylenes with various alkynes has been developed using a low-valent cobalt catalyst. The transformation has a wide substrate scope and high functional-group tolerance and led to 1,4-dihydronaphthalenes. The formed cycloadducts were easily aromatized with MnO2 under air. A mechanistic investigation suggests that the transformation proceeds through a benzyl cobaltation of alkyne, not the classical Diels-Alder reaction of ortho-quinodimethanes. This methodology provides a straightforward and streamlined access to linearly expanded π-conjugated aromatics.
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima City, Hiroshima 739-8527 (Japan). kkome@hiroshima-u.ac.jp.
authors.forename: Kimihiro
authors.initials: K
authors.lastname: Komeyama
authors.forename: Yuji
authors.initials: Y
authors.lastname: Okamoto
authors.forename: Ken
authors.initials: K
authors.lastname: Takaki
keywords: [4+2] cycloaddition; alkynes; cobalt; linear acenes; synthetic methods