Ruthenium-Catalyzed Tandem [2 + 2 + 2]/[4 + 2] Cycloaddition of 1,6-Heptadiyne with Norbornene

The ruthenium(II)-catalyzed reaction of a substituted 1,6-heptadiyne with norbornene gave a tandem [2 + 2 + 2]/[4 + 2] cycloaddition product as a single stereoisomer along with a [2 + 2 + 2] cycloadduct. CpRu(cod)Cl catalyzes both [2 + 2 + 2] cycloaddition of the heptadiyne and norbornene and subsequent [4 + 2] cycloaddition of the resultant cyclohexadiene and norbornene. The second [4 + 2] cycloaddition step was effectively improved by use of an indenyl complex, (η 5 -C 9 H 7 )Ru(PPh 3 ) 2 Cl, to afford the tandem adducts in moderate to good yields.