July 17, 2024, 06:21:32 AM
Forum Rules: Read This Before Posting


Topic: Unwanted Michael addition during deactylation; can we bring about an elimination  (Read 2989 times)

0 Members and 1 Guest are viewing this topic.

Offline Babcock_Hall

  • Chemist
  • Sr. Member
  • *
  • Posts: 5648
  • Mole Snacks: +327/-24
Hello Everyone,

We have four acetyl groups to remove in the presence of a vinyl sulfone (a glycosidic bond is also present).  We used about 0.5 equivalents of commercial NaOMe per acetyl group in dry, distilled methanol, which is about 10% as much as we used in our previous attempt.  We took time points using RP TLC at 60 an 90 minutes.  Although the 60 minute time point suggested that the reaction had not quite gone to completion, the 90 minute time point did not look appreciably different.  Therefore, we terminated the reaction using Dowex-50.  We saw what we believe is addition of a methoxide into the vinyl sulfone.  We still have more than half of the starting material.  I can think of a couple of things I would do differently.

For now however, I would like to use one of the two failed reaction products.  If we could bring about an elimination of the methoxide without harming the rest of the molecule, we would regenerate the vinyl group.  I was thinking about trying DBU, but I really don't have much of an idea concerning the optimal condition.  Does anyone have any suggestions?

Offline rolnor

  • Chemist
  • Sr. Member
  • *
  • Posts: 2250
  • Mole Snacks: +151/-10
Heat i important, DBU could work. You can make a stock solution of the starting material in DMF or diglyme and reflux this with different bases in very small scale. NaH maybe?

Offline Babcock_Hall

  • Chemist
  • Sr. Member
  • *
  • Posts: 5648
  • Mole Snacks: +327/-24
DABCO has also been suggested to me.

Offline rolnor

  • Chemist
  • Sr. Member
  • *
  • Posts: 2250
  • Mole Snacks: +151/-10
Yes you can make several small runs in vials and run TLC

Sponsored Links