{"id":11243,"date":"2018-02-09T06:58:07","date_gmt":"2018-02-09T11:58:07","guid":{"rendered":"https:\/\/www.masterorganicchemistry.com\/?p=11243"},"modified":"2026-04-19T04:26:19","modified_gmt":"2026-04-19T09:26:19","slug":"endo-exo-diels-alder-telling-them-apart","status":"publish","type":"post","link":"https:\/\/www.masterorganicchemistry.com\/2018\/02\/09\/endo-exo-diels-alder-telling-them-apart\/","title":{"rendered":"Exo vs Endo Products In The Diels Alder: How To Tell Them Apart"},"content":{"rendered":"

Today we’ll cover how to tell\u00a0endo<\/em>– and\u00a0exo-\u00a0<\/em>products apart in the Diels-Alder reaction. Shortcut below.\u00a0\u00a0For the long-winded walkthrough with lots of examples, read more below.<\/p>\n

\"quick<\/p>\n

Table of Contents<\/strong><\/p>\n

    \n
  1. Exo and Endo Products In The Diels-Alder<\/a><\/li>\n
  2. Exo And Endo Diels-Alder Products Are Diastereomers Of Each Other<\/a><\/li>\n
  3. 3-D Models Of The Endo And Exo Products In The Diels-Alder Between Cyclopentadiene And Maleic Anhydride<\/a><\/li>\n
  4. Distinguishing \u201dEndo” vs “Exo”: Pay Attention To The Relationship Between The “Outside” Groups On The Diene And The EWG On The Dienophile<\/a><\/li>\n
  5. Another Worked Example: Cyclopentadiene And Quinone<\/a><\/li>\n
  6. How Do You Know If A Diels-Alder Will Give You Endo<\/i> And Exo<\/i> Products?<\/a><\/li>\n
  7. Four More Examples (Including A Trick Question)<\/a><\/li>\n
  8. Transition States In A Diels-Alder That Does NOT Lead To Endo And Exo Products<\/a><\/li>\n
  9. Transition States In A Diels-Alder That Leads To Exo and Endo Products<\/a><\/li>\n
  10. So Why Is The Endo Product Favored?<\/a><\/li>\n
  11. Notes<\/a><\/li>\n
  12. Quiz Yourself!<\/a><\/li>\n<\/ol>\n
    \n

    <\/a>1. Exo and Endo Products in the Diels-Alder<\/h2>\n

    In this series of articles on the Diels-Alder reaction, we’ve seen that:<\/p>\n

      \n
    1. the Diels-Alder reaction always involves the breakage of 3 pi bonds and the formation of 3 new bonds (2 sigma, one pi), resulting in the formation of a new six-membered ring. [Intro<\/em><\/a>]<\/li>\n
    2. The stereochemistry of the dienophile is preserved. A cis<\/em> arrangement of groups in a double bond will result in a cis<\/em> arrangement in the new six-membered ring. And likewise,\u00a0\u00a0trans<\/em>\u00a0\u2192 \u00a0trans<\/em><\/li>\n
    3. For dienes, the two “outside” groups on the diene each end up on the same face of the new six-membered ring. Likewise, the two “inside” groups each also end up on the same face of the new ring.<\/li>\n<\/ol>\n

      (These last two parts are from the last post, where we went through the stereochemistry of the Diels-Alder reaction<\/a>.)<\/p>\n

      Now let’s add the next layer of detail.\u00a0 For certain diene\/dienophile combinations,\u00a0 we can end up with two<\/strong> products that fulfill all of those criteria. For instance:<\/p>\n

      \"a<\/p>\n

      <\/a>2. Exo And Endo Diels-Alder Products Are Diastereomers Of Each Other<\/h2>\n

      These two products are stereoisomers. But since they are\u00a0not\u00a0<\/em>non-superimposable mirror images (i.e. not enantiomers), they are diastereomers. hover here to view a pop-up image <\/a> [In fact, each of these molecules are achiral, due to the presence of a mirror plane – if you can’t see it, click here <\/a>]\u00a0<\/em><\/p>\n

      These two molecules can be separated due to the fact that they have different physical properties.<\/p>\n

      An as it turns out, the major product is the one above left. The minor is the one above right.<\/p>\n

      Sometimes it can help to look at these things in perspective:<\/p>\n

      \"diels<\/p>\n

      <\/a>3. 3-D Models Of The Endo And Exo Products In The Diels-Alder Between Cyclopentadiene And Maleic Anhydride<\/h2>\n

      Here are the two products again (major and minor) built as models.<\/p>\n