A transition-metal-catalyzed enediyne cycloaromatization.

The pentamethylcyclopentadienyl iron cation, generated from [(eta5-C5Me5)Fe(NCMe)3]PF6, triggers the room temperature cycloaromatization of acyclic and alicyclic enediynes, in the presence of either 1,4-cyclohexadiene or terpinene as the hydrogen-atom donor, to give metal-arene products in good to excellent yields. Photolysis of the metal-arene complexes liberates the arene from the metal in excellent yield. The first demonstration of a transition-metal-catalyzed cycloaromatization of conjugated enediynes has been achieved under photochemical conditions utilizing either [(eta5-C5Me5)Fe(NCMe)3]PF6 or [(eta5-C5Me5)Fe(eta6-1,2-(Prn)2C6H4)]PF6 as the catalyst precursor. The use of a metal and light has led to a convenient method for cycloaromatization of a trans-enediyne.