Abstract
Metathesis reactions are transformations of olefin and/or alkyne compoundsviacleavage and reassembly of CC double and/or triple bonds. Since the discovery of Ru‐ and Mo‐carbene catalysts, olefin metathesis has been applied to the natural product syntheses and drug discoveries. Enyne and alkyne metatheses have achieved great success in total syntheses of many important molecules as a complementary role of the olefin metathesis. As well as the Ru‐ or Mo‐catalyzed metathesis, skeletal reorganization of enynes and of hetero‐enyne metathesis bring about the efficient formation of unsaturated compounds. In the present chapter, typical examples for the synthesis of natural products and drugs according to a pattern for the metathesis protocols are described.