Cobalt-Catalyzed Intramolecular [4 + 2] Cycloaddition of Cyclopropyl-Capped Dienes with Alkynes/Alkenes/Allene and Reaction Mechanism

A cobalt-catalyzed intramolecular [4 + 2] cycloaddition of cyclopropyl (CP)-capped dienes with ynes/enes/allene was reported, providing an efficient method toward a spiro[2.5]octene ring system found in natural products, such as illudin. The [4 + 2] cycloadducts can be converted into other compounds via CP chemistry. This reaction can also be catalyzed by Ni. A density functional theory study on the reaction mechanisms is also reported here.