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Boc Protection

(Boc2O + DMAP)







Mechanism:



Boc protection mechanism using DMAP


Steps:

  1. DMAP attacks a carbonyl site on di-tert-butyl dicarbonate (Boc2O) resulting in tert-butyl carbonate leaving as a leaving group.
  2. The amine attacks the carbonyl site on the boc-pyridinium species resulting in the release of DMAP (catalytic).
  3. Tert-butyl carbonate picks up the proton from the protonated amine.
  4. Tert-butyl bicarbonate breaks down into CO2 (gas) and tert-butanol.

Key Points:

  1. The rxn of DMAP with Boc2O is almost instantaneous (gas formation!). To avoid rapid gas formation slowly add the DMAP over an appropriate period of time.
  2. The CO2 gas that forms during the rxn should be allowed to escape. Don't run boc protections in closed systems.
  3. DMAP should accelate the rate of the boc protection rxn but also makes side rxns more likely.



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