Ene–yne metathesis of polyunsaturated norbornene derivatives

Norbornene derivatives bearing endo-substituents in the 5- and 6-positions were studied as substrates for ene–yne metathesis cascades. Substrates which contained an internal alkyne and a terminal alkene or alkyne in each sidechain were found to undergo a metathesis cascade leading to pentacyclic bis-dienes and bis-trienes. Attempts to extend the chemistry further to sidechains containing two internal alkynes or two internal alkynes and a terminal alkene were not successful with the first generation Grubbsʹ catalyst. However, the substrate containing two internal alkynes did react with the second generation Grubbsʹ catalyst to give a tetra-diene containing product.