Formation of macrocycles via ring-closing olefin metathesis.

The enhanced metathesis activity of 1,3-dimesityl-4,5-dihydroimidazole-2-ylidene ruthenium carbene catalyst 3 significantly increases the feasibility of synthesizing macrocyclic compounds. Catalyst 3 exhibits sufficient activity in RCM to dimerize alpha,beta-unsaturated ester substrates and afford the corresponding head-to-tail (E,E)-dimeric (and trimeric) macrocycles. The dimerization appears to be under thermodynamic control with the product mixture dependent not only on the electronic and steric nature of the substrate but also on concentration.