March 28, 2024, 02:31:44 PM
Forum Rules: Read This Before Posting


Topic: Number of alpha hydrogens and effect on Robinson Annulation?  (Read 583 times)

0 Members and 1 Guest are viewing this topic.

Offline OrganicH2O

  • Regular Member
  • ***
  • Posts: 79
  • Mole Snacks: +3/-0
I have a question about how the number of alpha hydrogens effects the ease or Robinson Annulation. I attached a picture which illustrates my question.

In reaction 1 in the picture, the 1,3-diketone has two alpha hydrogens. Following Michael addition, the ground state would be the doubly stabilize enolate ion shown. I hypothesize that this stable enolate will slow down subsequent aldol cyclization. This aldol cyclization is possible, but  might require harsher conditions like higher temperature and longer reaction times.

In reaction 2, the 1,3-diketone has only one alpha hydrogen. Therefore, formation fo the an especially stable enolate is not possible. Subsequent aldol cyclization would therefore be much faster. It might even be impossible to stop the aldol cyclization.

Is this speculation logical and correct?
I have a Master's in organic chemistry and I am exposed to a LOT of different introductory organic chem classes in the course of my work, ranging from very basic to Harvard. I am here to refine my knowledge and consult with other organic chemistry nerds.

Sponsored Links