I am trying to come up with a logical mechanism for the following transformation, where 2-methylenecyclobutan-1-ol is converted to cyclopentanone under acidic conditions:

Acid-catalysed rearrangement of 2-methylenecyclobutan-1-ol to cyclopentanone

What I have tried to do was contract the ring to a methylcyclopropyl carbocation as it is exceptionally stable. I also tried to expand the ring but got an unsaturated primary alcohol instead. Can somebody suggest a proper mechanism for the reaction?

  • 3
    $\begingroup$ According to J. Chem. Soc., Chem. Commun. 1973, Vol. 4, 103–104: "On heating in a sealed tube at 245° for 4 h or on treatment with 5% H2SO4 at 100° for 30 min, (3) [your starting material] is quantitatively converted into 1-methylcyclopropanecarbaldehyde." This makes a lot more sense mechanistically, and is similar to a pinacol rearrangement: i.stack.imgur.com/UdU5b.png $\endgroup$ Oct 14, 2018 at 11:22
  • $\begingroup$ @orthocresol Yep, this is in agreement with what I know. Can you provide a more detailed explanation of this mechanism , and why it is the only correct one in the form of an answer? $\endgroup$ Oct 14, 2018 at 12:33
  • 1
    $\begingroup$ chemistry.stackexchange.com/questions/48739/… $\endgroup$ Oct 15, 2018 at 0:01


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