Synthesizing Higher para-Quinones Using Zirconacyclopentadienes

Significance

In the reported route to higher para-quinones, a zirconacyclopentadiene, formed by the reaction of two equivalents of an alkyne with a zirconium(II) species, reacts with a quinone to first form a dihydroquinone. The dihydroquinone is then aromatized by treatment with p-chloranil. The authors propose that the zirconacyclopentadiene undergoes a transmetallation with copper and that the resulting organocopper intermediate adds to the quinone. The above conditions are used to synthesize a variety of quinones, though the reaction with 1,4-benzoquinone is not successful, as previously reported by the authors.