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Metathesis

Olefin methathesis is an organic reaction that features the rearrangement of carbon-carbon double bonds by the redistribution of alkene fragments. It has led scientists to discover new disconnections in organic synthesis, paving the way for new advances in polymer chemistry, drug discovery, and natural product synthesis. There are three main classes of metathesis reactions, ring-closing metathesis and cross metathesis are utilized regularly for small molecule organic synthesis while ring-opening metathesis is frequently used for polymerization.

The most common and recognizable application of olefin metathesis in organic synthesis is ring-closing metathesis (RCM), an intramolecular reaction of an acyclic diene to form a ring. This methodology allows for the construction of all-carbon and heteroatom-containing rings that are rich in sp³-centers, a growing theme in modern medicinal chemistry.¹

Cross metathesis brings two olefins together in an intermolecular reaction to give an olefin product bearing substituent from each of the starting olefins. Excellent functional group compatibility, in addition to a tolerance of residual moisture and oxygen, have facilitated the broad acceptance of ruthenium-catalyzed macrocyclization as a general methodology for the preparation of large rings (≥12 atoms).²

Ring-opening metathesis polymerization (ROMP) designs polymers with tunable properties and has become a powerful technological advancement in the arena of facilitated synthesis. Due to the low cost and readily available starting materials, this robust polymerization methodology can be used to produce polymers on a large scale.³

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Ring-closing metathesis is an intramolecular reaction of an acyclic diene to form a ring.

Figure 1.Ring-closing metathesis (RCM)

Ring-opening metathesis is driven by the is driven by the force to relieve ring strain. In absence of excess of a second reaction partner, polymerization occurs (ROMP).

Figure 2.Ring-opening metathesis (ROM(P))

Cross metathesis brings two olefins together in an intermolecular reaction to give an olefin product bearing substituent from each of the starting olefins.

Figure 3.Cross Metathesis (CM)

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References

1.

Lovering F, Bikker J, Humblet C. 2009. Escape from Flatland: Increasing Saturation as an Approach to Improving Clinical Success. J. Med. Chem.. 52(21):6752-6756. https://doi.org/10.1021/jm901241e

2.

Blackwell HE, Sadowsky JD, Howard RJ, Sampson JN, Chao JA, Steinmetz WE, O'Leary DJ, Grubbs RH. 2001. Ring-Closing Metathesis of Olefinic Peptides: Design, Synthesis, and Structural Characterization of Macrocyclic Helical Peptides. J. Org. Chem.. 66(16):5291-5302. https://doi.org/10.1021/jo015533k

3.

Harned A, Zhang M, Vedantham P, Mukherjee S, Herpel R, Flynn D, Hanson P. 2005. ROM Polymerization in Facilitated Synthesis. Aldrichimica Acta. 38, 3-16. https://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/Aldrich/Acta/al_acta_38_1.pdf