--- title: "Olefin Metathesis and Ring-Closing Strategy" description: "Metathesis exchanges the ends of two alkenes through a metallacyclobutane, and the equilibrium is usually driven by loss of a small volatile alkene. That single reaction turns a long diene into a ring" canonical: https://lightmysky.com/learn/science/olefin-metathesis-and-ring-closing-strategy-mt_J9UAxKsgSk source: https://lightmysky.com/learn/science/olefin-metathesis-and-ring-closing-strategy-mt_J9UAxKsgSk.md retrieved: 2026-09-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Olefin Metathesis and Ring-Closing Strategy Metathesis exchanges the ends of two alkenes through a metallacyclobutane, and the equilibrium is usually driven by loss of a small volatile alkene. That single reaction turns a long diene into a ring, which changes how a synthesis is planned. Subject: Science · Area: Chemistry · Ages 23 to 24 Page: https://lightmysky.com/learn/science/olefin-metathesis-and-ring-closing-strategy-mt_J9UAxKsgSk ## Ready when they can - Draws the metallacyclobutane and shows how it accounts for the exchanged fragments - Predicts the ring formed from a stated diene and names what drives the reaction forwards - Explains why high dilution favours ring closing over chain extension - Chooses between a metathesis disconnection and a carbonyl disconnection for a macrocyclic target ## Lesson: Trading ends to close a ring Metathesis swaps the ends of two alkenes. Each alkene splits and the halves trade partners, and the trade passes through a four-membered ring that holds the metal: the metallacyclobutane. If you can draw that ring, you can account for every fragment in the products. You need no handle on either bond; the metal does the swapping. **Example.** Picture a long chain with an alkene at each end. The metal joins the two ends, the chain becomes a ring, and the leftover ends pair up into a small alkene that escapes as a gas. That escape matters: with product leaving, the back reaction starves and the mixture moves forward. To find the ring size, count the chain atoms and subtract the atoms carried away by the small fragment. Now put one diene in a big flask of solvent. Its two ends meet each other far more often than two separate molecules meet, so the molecule closes into a ring. Crowd the flask and the picture flips: molecules bump into neighbours, chains grow, and rings lose. When you want rings, dilute; when you want chains, concentrate. **Tip.** When you plan a large ring, look at its ends. If you can cut the ring at a bond that leaves an alkene on each side, metathesis can stitch it shut, while a carbonyl route with its matching polar handles may fit worse. Choose the cut whose ends your reaction can actually join. **Recap.** You trade alkene ends through a four-membered ring, let the escaping fragment pull you forward, and dilute when you want a ring. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Functionalising a Carbon-Hydrogen Bond Without a Handle](https://lightmysky.com/learn/science/functionalising-a-carbon-hydrogen-bond-without-a-handle-mt_j0LaIeS2VP) - [Organometallic Ligands: Carbonyls, Phosphines and Hapticity](https://lightmysky.com/learn/science/organometallic-ligands-carbonyls-phosphines-and-hapticity-mt_JXYSQDYlJ-) ## Opens up - [Photoredox and Electrochemical Routes to Radical Intermediates](https://lightmysky.com/learn/science/photoredox-and-electrochemical-routes-to-radical-intermediates-mt_YhqzHGcx31)