3.5.6.3 Cycloaddition

Dicobalt octacarbonyl can be converted into (η5 -cyclopentadienyl)dicarbonylcobalt(0) which is the catalyst for Volhardt cyclotrimerization reaction. This reaction is unique as it brings about the formation of a benzene ring in one step by [2+2+2] cycloaddition of a dialkyne with a monoalkyne (Scheme 7).

Scheme 7