(Oxolan-2-yl)methanol + H+

I think the ethereal oxygen in THFA gets protonated. Due to greater +I effect, the electron density on it is higher, hence it is more likely to behave as a Lewis base. Consequently, the product formed is pent-2-en-1,5-diol:

(Oxolan-2-yl)methanol + H+ to pent-2-en-1,5-diol

Apparently, this is wrong. What exactly happens here and why my answer is wrong?


1 Answer 1


The alcohol group of your educt (tetrahydrofurfuryl alcohol) is protonated, and after subsequent loss of water, the resulting primary carbocation can rearrange to a more stable 6-membered ring cation, which is stabilized by resonance. Initial protonation at the ether oxygen is therefore disfavored, as it will not result in the formation of a similarly stable carbocation (with positive charge adjacent to oxygen). After final deprotonation, 2,3-dihydropyran is obtained.

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  • $\begingroup$ The arrow in the third step should be from the C-C bond, not the C-O bond. $\endgroup$
    – 1__
    Commented Apr 17, 2023 at 1:50
  • $\begingroup$ @Lemoine Thanks for catching that, I've corrected the mechanism. $\endgroup$ Commented Apr 17, 2023 at 18:26

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