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30: Rearrangements

  • Page ID
    151241
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    Funky Rearrangements

    PASSPORT: Review Hydride Shifts

    1,2 Hydride Shifts

    The reaction of 3-methyl-1-butene with HCl gives 40% of 2-chloro-3-methylbutane product and 60% of the 2-chloro-2-methylbutane product.

    • Draw a mechanism to explain these results.

    Rearrangements are extraordinarily common in carbocation chemistry. 1,2 –migration of hydride (hydride shifts) are among the fast reactions known.

    • When and why do these reactions occur readily?

    Meerwein-Wagner Rearrangements

    Alkyl Shifts (Meerwein-Wagner Rearrangements) are also common.

    • Write a mechanism for the following reaction:

      Screen Shot 2019-05-21 at 2.29.47 AM.png

    • Write a mechanism for the following reaction:

      Screen Shot 2019-05-21 at 2.31.50 AM.png

    Rearrangements to Electron Deficient Centers

    (Almost Cationic)

    Screen Shot 2019-05-21 at 2.34.26 AM.png

    Pinacol Rearrangement

    • Provide a mechanism for the following transformation

      Screen Shot 2019-05-21 at 2.37.16 AM.png

    • Why is th Pinacol Rearrangement favored over an elimination or a substitution reaction?

    Beckman rearrangement

    Screen Shot 2019-05-21 at 2.39.06 AM.png

    This rearrangement begins with the use of an oxime

    • Review: How would you make the oxime?

      Screen Shot 2019-05-21 at 2.40.39 AM.png

    • Provide a mechanism for the following transformation. Remember alkyl shifts will move to carbocation centers or other electron deficient atoms.

      Screen Shot 2019-05-21 at 2.42.51 AM.png

    Baeyer-Villager Rearrangement

    Screen Shot 2019-05-21 at 2.43.28 AM.png

    • Provide a mechanism for the following transformation. Remember alkyl shifts will move to carbocation centers or other electron deficient atoms.

      Screen Shot 2019-05-21 at 2.45.37 AM.png

    • Review: When have you seen this reagent before? What other reactions does it do?

    Wolff Rearrangment

    Screen Shot 2019-05-21 at 2.53.11 AM.png

    • Draw Lewis electron dot structure for diazomethane, CH2N2.
    • Provide the mechanism for the following transformation

      Screen Shot 2019-05-21 at 2.55.39 AM.png

    • Provide a mechanism for the following transformation. Remember alkyl shifts will move to carbocation centers or other electron deficient atoms.

      Screen Shot 2019-05-21 at 2.57.48 AM.png

    This reaction is quenched with nucleopholes such as water.

    • Draw the product for the reaction of the ketene above with water.
    • This carbene intermediate can be used in other ways. Using what you know about carbenes, predict what the product of this reaction will be.

      Screen Shot 2019-05-21 at 3.03.58 AM.png

    Curtius Rearrangement

    Screen Shot 2019-05-21 at 3.04.56 AM.png

    This is almost the same reaction except that sodium azide is added rather than diazomethane.

    • Draw Lewis electron dot structure for sodium azide, NaN3.
    • Provide a mechanism for the following transformation.

      Screen Shot 2019-05-21 at 3.08.08 AM.png

    • The isocyanate product above is very sensitive to nucleophilic attack. Draw the reaction of this isocyanate with methanol

    Hoffman Rearrangement

    Screen Shot 2019-05-21 at 3.10.06 AM.png

    The Hoffman rearrangement also involves the formation of an isocyanate in a related rearrangement.

    • Provide a mechanism for the following transformation

      Screen Shot 2019-05-21 at 3.12.18 AM.png

    The isocyanate product above quickly reacts with the OH- in solution to form the carbamic acid.

    • Draw the product formed

    Carbamic acid is quickly deprotonated and spontaneously decarboxylates to form a primary amine.

    • Draw this mechanism

    Summary Page

    30 Rearrangements-08.jpg

    Additional Problems

    1. The synthesis of Perhydrohistrionicotoxin by E.J. Corey in 1975 displays the utility of some of these rearrangements.

      30 Rearrangements-09.jpg

    2. Draw mechanisms for the following changes.

      Screen Shot 2019-05-21 at 3.20.55 AM.png

    3. Provide a mechanism for the following transformation of morphine into apomorphine. Remember Meerwein-Wagner Rearrangemnts, This is hard!

      Screen Shot 2019-05-21 at 3.22.59 AM.png


    This page titled 30: Rearrangements is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Kate Graham.

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