text: Ring-closing Metathesis has shown utility in the synthesis of 5-30 membered rings, polycycles, and heterocycles containing atoms such as N, O, S, P, and even Si. Due to the functional group tolerance of modern RCM reactions, the synthesis of structurally complex compounds containing a range of functional groups such as epoxides, ketones, alcohols, ethers, amines, amides, and many others can be achieved more easily than previous methods. Oxygen and nitrogen heterocycles dominate due to their abundance in natural products and pharmaceuticals. Some examples are shown below (the red alkene indicates C-C bond formed through RCM).
  In addition to terminal alkenes, tri- and tetrasubstituted alkenes have been used in RCM reactions to afford substituted cyclic olefin products. Ring-closing metathesis has also been used to cyclize rings containing an alkyne to produce a new terminal alkene, or even undergo a second cyclization to form bicycles. This type of reaction is more formally known as enyne ring-closing metathesis.